United States

Department of

Agriculture Ecology and

Forest Service

Pacific Northwest

Forest and Range Manageme t of the

Experiment Station

General Technical Spotted Owl PNW-185

September 1985

0

Pacific Northwest

54:

c.7DIu.
be suitable. .e
Ecology and Management of the

Spotted Owl in the

Pacific Northwest

Arcata, California

June 19-23, 1984

Ralph J. Gutierrez and Andrew B. Carey

Technical Editors

Sponsored by:

Cooper Ornithological Society

Humboldt State University

USDA Forest Service, Pacific Southwest Forest and Range

Experiment Station

USDA Forest Service, Pacific Northwest Forest and Range

Experiment Station

Published by:

U.S. Department of Agriculture, Forest Service

Pacific Northwest Forest and Range Experiment Station

Portland, Oregon

General Technical Report PNW-185

September 1985
CONTENTS

l

Page

INTRODUCTION -- Ralph J. Gutiérrez and Andrew B. Carey . . . . . . . . . . . . . . . . . . . . . 1 6

MANAGEMENT FOR SPOTTED OWLS

Planning and Managing for the Spotted Owl in the National Forests,

Pacific Southwest Region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

W. Dean Carrier

History and Current Status of Spotted Owl (Strix occidentalis) Habitat Management

in the Pacific Northwest Region, USDA, Forest Service. . . . . . . . . . . . . . . . . . . 5

Philip L. Lee

Implementing a Spotted Owl Management Plan: The Gifford Pinchot National

Forest Experience. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

William C. Ruediger

Olympic National Forest Spotted Owl Habitat Management: Translating

Evolving Management Guidelines into Actions. . . . . . . . . . . . . . . . . . . . . . . . 14

Maureen A. Beckstead

Management of Spotted Owls by the California Department of Fish and Game . . . . . . . . . . 21

Gordon I. Gould, Jr.

Status of Spotted Owl Management in Oregon as Perceived by Oregon Department

of Fish and Wildlife . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Richard D. Carleson and William I. Haight

Managing Northern Spotted Owls in Washington: The Position of the Washington

Department of Game . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Tom Juelson

Spotted Owl Management: Meeting NFMA Requirements Through Monitoring. . . . . . . . . . . . 34

Andrew B. Carey and Leonard F. Ruggiero

RECENT RESEARCH ON SPOTTED OWLS

An Overview of Recent Research on the Spotted Owl. . . . . . . . . . . . . . . . . . . . . . 39

R. J. Gutiérrez

Breeding Success Relative to Fluctuations in Diet for Spotted Owls in California . . . . . . 50

Cameron W. Barrows

A Review of Current Northern Spotted Owl (Strix occidentalis caurina) Research

in Washington State. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

Harriet L. Allen and Larry W. Brewer

Old-Growth Forest Retention for Spotted Owls--How Much Do They Need? . . . . . . . . . . . . 58

Eric D. Forsman and E. Charles Meslow

Juvenile Spotted Owl Dispersal in Northwestern California: Preliminary Results. . . . . . . 60

R. J. Gutiérrez, Alan B. Franklin, William Lahaye, Vicky J. Meretsky,

and J. Patrick Ward

General Habitats and Movements of Spotted Owls in the Sierra Nevada. . . . . . . . . . . . . 66

Stephen A. Laymon

Dispersal Data for Juvenile Spotted Owls: The Problem of Small Sample Size. . . . . . . . . 69

Gary S. Miller and E. Charles Meslow

n

F

5

.-%.

r
APPLICATION OF POPULATION THEORY TO SPOTTED OWL MANAGEMENT

The Demography and Population Genetics of Owls, With Special Reference to the

Conservation of tha Spotted Owl (Strix occidentalis) . . . . . . . . . . . . . . . . . . . 14

George F. Barrowclough and Sadie L. Coats

The Metapopulation and Species Conservation: The Special Case of the Northern

Spotted Owl. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86

Mark L. Shaffer

IMPLICATIONS OF THE ACCUMULATED INFORMATION FOR SPOTTED OWL MANAGEMENT

A Summary of the Scientific Basis for Spotted Owl Management . . . . . . . . . . . . . . . 100

Andrew B. Carey

Information and Research Needs for Spotted Owl Management. . . . . . . . . . . . . . . . . 115

R. J. Gutiérrez

English and Metric Equivalents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 '
INTRODUCTION

RALPH J. GUTIIERRZ AND ANDREW B. CARRY

The spotted owl, Strix occidentalis, has become a

species of concern to ornithologists, wildlife

biologists, foresters, and environmentalists

because of its apparent need for old-growth

coniferous forest in the Pacific Northwest.

Because of the concern about spotted owls, a

symposium was convened by the Cooper

Ornitholoical Society during its annual meeting

in 1984. 1/ The society wished to bring

concerns about spotted owls before public,

scientific scrutiny. Gutiérrez was asked to

arrange the symposium, and Carey was invited to

cochair the symposium. Together, we expanded the

objectives of the symposium and planned this

publication.

A.

1

/ The 54th Annual Meeting of the Cooper

Ornithological Society, 1984 June 19-23, Arcata,

CA.

The symposium was organized into three sections:

management, research, and theory. We felt that

an understanding of the laws and regulations

governing Federal land management, the state of

spotted owl management, the biology of spotted

owls, and the predictions of ecological theory

were all essential for planning and evaluating

future research and management for the spotted

owl. We wished to bring this information

together in an arena of unconstrained discussion

and exposition of ideas. Thus we invited both

managers and researchers dealing with spotted

owls and theoretical biologists who did not have

experience with the spotted owl. Because we had

limited time for presentations, not all papers

published here were presented at the symposium.

We have included the unpresented papers to ensure

a published report that would be a complete

treatment of spotted owl research and management

in the Pacific Northwest.

1
PLANNING AND MANAGING FOR THE SPOTTED OWL IN THE

NATIONAL FORESTS, PACIFIC SOUTHWEST REGION

W. Dean Carrier

ABSTRACT: The spotted owl (Strix occidentalis caurina) has been listed as a

sensitive species by the Pacific Southwest Region USDA Forest Service. Past

and present-studies-and surveys have led to the development of a region-wide

network of owl territories to comply with the maintenance of viable

populations as required by the National Forest Management Act. A brief

explanation of the network is included.

HISTORY

In 1973 and 1974, the California Department of

Fish and Game and the USDA Forest Service funded

an inventory of spotted owls to better understand

the status of this species in California. This

work was carried out by Gould (1977) and resulted

in a state-wide population estimate of 192 pairs

in five major population concentrations.

During this period individual Forests also began

to assess owl populations and habitats and to

consider owls in Forest multiresource management

activities. Fairly intensive surveys of

suspected owl habitats were carried out in at

least four National Forests.

W. DEAN CARRIER is the threatened and endangered

species biologist for the Pacific Southwest

Region of the USDA Forest Service, San Francisco,

Calif.

Following the passage of the National Forest

Management Act of 1976 (NFMA) and the issuance of

the regulations implementing it, the Forest

Service began to assess many wildlife and fish

species to ensure that viable populations were

being maintained, as the Act requires. The

spotted owl, because of its purported need of

old-growth coniferous habitats, became the focal

point of this requirement.

In 1978 the Oregon Interagency Task Force

developed a habitat management plan and

population requirements for spotted owls on

public lands in Oregon. The Pacific Southwest

Region followed this lead and began to assimilate

data on spotted owl populations and habitat use

in National Forests in California. Between 1975

and the present (1984) the Region has initiated,

funded, or assisted in no less than 10 individual

research projects or status evaluations of

spotted owls.

zBecause the Pacific Southwest Region chose to

treat both subspecies of spotted owl (Strix

2
occidentalis caurina and S. o. occidentalis)

identically, the system used-is based on the

Oregon-Washington Interagency Wildlife

Committee's plan with one major exception. This

:+ exception is that the actual assessment and

allocation of numbers of territories is relegated

to the individual Forests.

0

u PLANNING STRATEGY

Using known habitat requirements, as taken from

available research data, the task of identifying

the numbers and networks of territories to be

maintained was assigned to each Forest. TO

determine these population goals, the Regional

plan established guidelines for developing an

interacting network of spotted owl territories

that would be distributed throughout the

geographic range of the species in California

north of the Tehachapi Mountains. The criteria

provide for grouping, spacing, and specific

characteristics of spotted owl territories. The

criteria were based on data collected in Oregon

and in the numerous local studies that had been

conducted in the National Forests of northern

California, and on the west slope of the Sierra

Nevada range. Habitat requirements were based

heavily on the studies by David Solis in the Six

Rivers National Forest and by Steve Laymon in the

central Sierra Nevada.

It must be stressed that the development of a

h

Regional network, based on a predetermined set of

habitat conditions necessary to provide for

spotted owl occupancy, was mainly an exercise in

modeling National Forest management activities as

-3 they relate to and interact with other resource

and land uses. In other words, on-the-ground

maintenance of individual territories may differ

under the standards developed for Land Management

Planning. As with most species, local habitat

conditions and long-term adaption to specific

situations may well be important factors in the

success of individual pairs. Broad standards and

guidelines cannot encompass all these factors;

thus, local adjustments are necessary when

actively applying these guidelines to specific

areas of land. The modeling assesses the overall

costs in terms of other forest resources of

maintenance of spotted owl habitat, and

on-the-ground application provides for the actual

needs of the individual pairs making up this

network.

The system for spotted owl habitat maintenance in

the Pacific Southwest Region was based on the

best information available. This is not to say

that we have all the answers; however, our

methods were designed to provide for the

currently documented needs of this species.

4

Research in the Pacific Northwest and California

was reviewed and used in the development of our

criteria. The pioneering work of the Oregon

Interagency Spotted Owl Task Force and the

-=f! subsequent development of the guidelines for

maintaining viable populations of spotted owls in

that State were major factors used in the

development of the Pacific Southwest Region's

system.

SPOTTED OWL TERRITORIES

The first level of the network is the territory.

Territories are areas suitable for maintaining

one breeding pair of owls. The ecological

characteristics of territories have been

determined through research and then translated

into vegetative components. For the most part, a

territory is comprised of a core area within

which the nest site, or probable nest site, is

located. This area is to contain 300 acres of

suitable habitat. If this amount is not

available, the existing stand is maintained. In

addition to this core area, an additional 700

acres of habitat within l-1/2 miles of the nest

site will be maintained in no more than three

parcels, one of which must suffice as an

alternate core area.

GROUPED TERRITORIES

The second level of this system is the grouped

territories (formerly called Spotted Owl Management Areas or "SOMAS"). These are normally

comprised of three individual territories spaced

within l-1/2 miles of each other. Some overlap

is allowed in providing acreage requirements for

the three territories.

FOREST NETWORK

The third level of the system is the Forest

network. This provides for a system of

interacting groups of territories spaced

throughout the known geographic range of the

spotted owl in that Forest. The network provides

for spacing of these groups between 6 and 12 miles

apart although single territories can be no

further than 6 miles from adjacent ones.

INTERACTING NETWORKS

The fourth level is the interacting network

between National Forests and other public and

private land areas maintaining spotted owl

habitat. Forests are required to coordinate with

adjacent land managers and their networks are

reviewed and approved by the Regional Forester.

CURRENT STATUS

Territories for spotted owls have now been

delineated in all National Forests, with the

exception of the five southern Forests where all

known territories will be protected. Using

currently accepted survey techniques, territories

are presently being verified and boundaries

further refined.

The network for National Forest lands in

California will provide for approximately 500

pairs. This is exclusive of those pairs that are

not a part of the network, but are protected by

other land management constraints (e.g.,

wilderness) and those owls in the five southern

Forests. Other resource management agencies and

3
private lands will provide additional territories

to add to the overall maintenance of spotted owls

in California.

DISCUSSION

The managing of lands to provide for the needs of

late vegetative successional species is a new and

inexact art, at best. For years, we have had the

ability to set back succession for the enhancement

of deer, quail, and pheasants; to modify habitat

for turkeys, grouse, and elk; or to protect

habitats for many other species. There is,

however, little evidence of purposeful management

to speed up or manage for vegetative succession

to provide for those habitats that are developed

at the climax end of succession.

In implementing this system we are assuming that

the spotted owl will maintain viable populations

over time. But, how will we know if the system

is working? What additional research is needed

to assure this? Are known changes caused by land

management activities or a natural sequence of

events? These are but a few of the many

questions that are asked of us as we try to

measure the exactitudes, demanded by the

scientific community, with experimental land

management schemes based on state-of-the-art @

information. It is doubtful that there will ever

be "enough" information. As natural and

human-caused changes occur in these ecosystems,

wildlife population will fluctuate accordingly, t

but probably not altogether predictably. Who

will be the one to decide whether global climatic

changes, as predicted by some hydrologists, or

artifical habitat changes are responsible for

population fluctuations in species.

LITERATURE CITED

Gould, Gordon I., Jr. Distribution of the spotted

owl in California. Western Birds. 8: 131-146;

1977.

4
HISTORY AND CURRENT STATUS OF SPOTTED 0WL (STRIX OCCIDETALIS) HABITAT

MANAGEMENT IN THE PACIFIC NORTHWEST REGION, USDA, FOREST SERVICE

Philip L. Lee

ABSTRACT : AS information has become available on the status of the

spotted owl and its habitat needs, the emphasis on managing for the owls

has increased on National Forests. Management of old-growth forests has

evolved from rapid conversion of the stands to young timber to the

acceptance of the need to retain this special habitat for species such as

the spotted owl. Detailed direction for the assessment and development

of spotted owl habitat during Forest Planning has been given to National

Forest Supervisors by the Regional Forester.

INTRODUCTION

Prior to 1970 little was known about the spotted

owl (Strix occidentalis) or its habitat in the

forests and it was not given any priority in

management of National Forests. What little

data existed on the owl indicated it was rare

and that few sightings had been made. During

the early 1970's, as work progressed on

legislation for the management and protection of

threatened and endangered species, the spotted

owl was proposed as "threatened" by the USDI

Fish and Wildlife Service (U.S. Department of

Interior, Fish and Wildlife Service 1973).

studies, enough was learned about it to question

the need for a Federal listing. As a result the

owl was not listed at the Federal level but was

classified in Oregon as threatened and in

Washington as a sensitive species. The spotted

owl was given the designation "sensitive" by the

Regional Forester, Pacific Northwest Region of

the Forest Service (Region 61, and thus was

afforded special consideration by management.

Following passage of the National Forest

Management Act in 1976 regulations were written

for implementation of the Act. These

regulations gave special emphasis to the spotted

owl because it met many of the criteria for a

"management indicator species". Those criteria

(Code of Federal Regulations, 36 CFR 219.19(l))

were: (1) that decreases in spotted owl

populations indicated potential negative effects

of planned management programs; (2) the owl was

on the threatened species list in Oregon; (3)

the owl was a species of special interest; and

(4) the owl represented other species that were

dependent upon a major biological community, the

old-growth forest.

As more people began to look for the owl, and

-4. particularly as it became the object of graduate

PHILIP L. LEE is Range, Watershed, Fish and

Wildlife staff officer, Siuslaw National Forest,

Pacific Northwest Region, USDA Forest Service,

Corvallis, OR.
In the short time that the spotted owl has been

of special interest a lot of information

concerning its life history and habitat

requirements has been collected. New

information has required a continual change in

management direction by Federal land managers.

This change is evident in the numerous memoranda

and letters between the various agencies and

interest groups and in direction being developed

for Forest Planning, which I review in this

paper.

EARLY PLANNING AND MANAGEMENT STRATEGIES

It is not my intent to go into the details of

the early planning efforts regarding numbers of

owls or habitat requirements. It is important

to note, however, the evolution of acceptance of

biological Information and the development of

direction for management of National Forest

lands for spotted owls.

An interagency committee made up of biologists

from the Forest Service, Bureau of Land

Management, Fish and Wildlife Service, Oregon

Department of Fish and Wildlife, and Oregon

State University was formed in 1973 to prepare

the first Spotted Owl Management Plan.

Objectives of the plan were to determine the

number and distribution of spotted owls in

Oregon and to recommend habitat management

practices. The recommendations coming from this

first effort were so controversial that on

August 16, 1973, the Regional Forester (Region

6) and the State Director of the BLM in Oregon

issued a joint statement that it was undesirable

to retain 300 acres of old-growth timber around

every known spotted owl nest site. Reasons

given were: "(1) rigidly cast prescriptions

tend to become the accepted practice...; (2) it

appears reasonable to assume that the present

old-growth stands located within acceptable

elevation limits, contain spotted owl

populations...; (3) we are confident that

further analysis will verify that sufficient

old-growth timber stands exist to provide

interim . . .protection.... (4) determination of

the desired State-wide production level...should

be resolved before total protection of all

sighting areas...is undertaken...and; (5) the

management by individual animal location

philosophy, when applied to all species...

presents a land management spectre of

considerable magnitude." Management of oldgrowth timber is a sensitive issue, and there

was a desire by some to liquidate the old growth

and replace it with young forests. Agency

managers were cautious in making decisions that

set aside large acreages of old-growth forest

until more evidence supported the need.

During the next 3 years evidence continued to

come from research and in 1976 the Regional

Forester issued direction that "Known nesting

sites will be protected until BUMP'S (Biological

Unit Management Plans) were developed..."

(memorandum from Region 6 Director of Fish and

Wildlife Management November 24, 1976). At this

same time the BLM suggested that several

enclaves where birds were concentrated should be

set aside and not harvested for 10 years, during

which time investigation would continue.

Management recommendations and a statewide goal

of 400 pairs of nesting spotted owls were

established from the first Oregon Spotted Owl

Management Plan. In January 1977 the Oregon

Endangered Species Task Force recommended to the

Regional Forester a proposal for interim spotted

owl guidelines. These guidelines, supplementing

the 1976 long-range goal of 400 pairs of spotted

owls in Oregon were: (1) for one year--1977--

protect all nests and areas where the owls had

been sighted; and (2) during that year the task

force would develop objectives and management

prescriptions to meet the goal and also identify

the number and distribution of habitats needed

to maintain a viable population in Oregon.

In May 1977 the Regional Forester responded to

the task force that the National Forests would

protect spotted owl habitat as recommended

except where timber sales already existed or

were planned for sale in 1977. The task force

was able to keep its commitment and issued a

review copy of the "Spotted Owl Management Plan"

on November 3, 1977. The intent was to continue

to obtain data and update the plan as needed.

The next update occured in May 1979. Biologists

from the State of Washington also joined in the n

planning process and there is now an Oregon-Washington Interagency Wildlife Committee that

considers matters pertaining to the spotted owl,

along with other concerns. F

Region 6 Spotted Owl Management Guidelines as

based on the management plan, were appealed by

the Oregon Wilderness Coalition on the

assumption that spotted owl habitat would not be

adequately protected. As a result of this

appeal, a new effort was made to insure that

minimum viable populations would be protected

while Forest Planning was in process. The

details for this action were described by

memoranda in 1980 from the Regional Forester to

Forest Supervisors. In March 1981 the

Interagency Committee recommended that the

guidelines be revised to include the option of

providing 1,000 acres of old-growth timber per

pair until research more clearly defines the

habitat needs of the owl.

In May 1981 a "Draft Pacific Northwest Region

Plan" was issued by the Regional Forester. This

plan included the proposed revision of the

Oregon Interagency Spotted Owl Management Plan.

This document set recommendations on size and

distribution of habitat and populations by

ownership and described spotted owl habitat. In

May 1984 the draft became the "Regional Guide

6
for the Pacific Northwest Region." 1/

Direction for spotted owl habitat management

planning is included in that document and is

discussed later in this paper.

CURRENT NATIONAL DIRECTION

B

Recent U.S. Department of Agriculture direction

that affects the spotted owl is Departmental

Regulation Number 9500-4 dated August 22, 1983.

The following excerpts show how this regulation

emphasizes the requirements of management and

planning under the National Forest Management

Act.

"It is the policy of the Department to assure

that the values of fish and wildlife are

recognized, and that their habitats...are

recognized and enhanced, where possible...

"A goal of the Department is to improve, where

needed, diverse, native...populations of

wildlife... while fully considering other

department missions...

"Habitats for all existing native...species...

will be managed to maintain at least viable

populations of such species...habitat must be

provided for the number and distribution of

reproductive individuals to ensure the continued

existence of a species throughout its geographic

range.

.c "Habitat goals... will be established and

implemented. This will be accomplished through

the Forest planning process...Habitat goals will

.g be coordinated with State Comprehensive Plans

developed cooperatively."

The Secretary established a Fisheries and

Wildlife Issues Working Group to monitor

implementation of the regulation and to

coordinate management with other Federal and

State agencies. This direction was incorporated

in Forest Service Manual 2603 in June 1984 and

the policy for "Wildlife, Fish and Sensitive

Plant Habitat Management" was updated.

CURRENT FOREST PLANNING DIRECTION IN REGION 6

In the draft regional plan each Forest was

assigned a number of pairs of owls to be used in

development of the Forest plans. These numbers

were to be tested in the planning process to

determine their validity. A total of 375 pairs

were assigned to the Forests, 263 in Oregon and

112 in Washington (the 400 pairs for Oregon

mentioned earlier included all ownerships, not

just National Forests). These numbers

.a.

represented the minimum viable populations. In

addition, four population levels representing

different management alternatives were developed

and Forest Supervisors were instructed to model

at least the minimum and the minimum plus 30

percent when assessing the impacts on other

resources. This direction was, in part, a result

of a task force recommendation following the

appeal of the Oregon Wilderness Coalition. This

action brought a response from the Northwest

Timber Association members who strongly protested

the consideration of an area 1,000 acres in size.

On September 19, 1980, the Regional Forester

clearly stated to Forest Supervisors in a

memorandum (2670), that "...you not forgo your

options to manage for owl population levels in

your Forest Plan other than your tentative

allocation in response to public involvement...

There will be a continuing public involvement

process as Forest Plans are developed, and any

long-term decisions concerning spotted owl

habitat will follow this process.

In April 1983 Region 6 established a task force

to address concerns about the assumptions of

models that were used to simulate management

that would meet minimum management requirements

for wildlife benchmark assessments (a benchmark

is a habitat base to which all alternatives are

compared to show the effects of alternatives on

other resources and on the population of a

species selected). Reviews by the Chief and the

Pacific Southwest Region of the Forest Service

raised some questions about the two methods used

to model spotted owl habitat management. The

two approaches used were: (1) to dedicate the

areas to spotted owl management and defer timber

harvest as long as the area meets habitat

requirements; and (2) to manage the areas for

timber while meeting minimum requirements for

the owls. The dedicated method simply sets the

habitat aside and no programmed timber harvest

occurs. The managed approach provides for

timber harvest over a long rotation either as

clearcuttings or harvesting individual trees.

The task force determined (unpublished report)

that two variables affected the efficiency of

timber management while managing spotted owls:

(1) the definition of old growth, especially the

rotation age; and (2) the size of the old-growth

stand. Because of this and other studies for

different Forests, Region 6 planning efforts

will evaluate both methods or a combination

where appropriate.

On February 9, 1983, the Regional Forester sent

"Regional Guidelines for Incorporating Minimum

Management Requirements in Forest Planning" 2/

to the Forest Supervisors. The reason for

Regional direction for minimum management

-s

.&/Unpublished Administrative Document, 1984,

"Regional Guide for the Pacific Northwest

Region", on file, Pacific Northwest Regional

Office, USDA Forest Service, 319 S.W. Pine

Street, Portland, OR 97208.

z/Unpublished Administrative Document, 1983,

"Regional Guidelines for Incorporating Minimum

Management Requirements in Forest Planning," by

Jeff M. Sirmon, Regional Forester, Pacific Northwest Regional Office of the USDA Forest Service,

319 S.W. Pine Street, Portland, OR 97208.

7
requirements (MMR) for wildlife was to insure

consistency across the Region in meeting

National direction. MMRs also serve as baseline

constraints for developing benchmarks and

alternatives. These MMRs were not to be

construed as alternatives in themselves. The

number of spotted owls designated for each

Forest was based on Region-wide information.

Because these numbers were only approximate,

each plan alternative would be measured against

the MMRs and a determination made whether that

alternative was meeting the intent of the law.

Using this direction, the Forests in Region 6

began to choose the areas that would be managed

for spotted owls to meet the MMRs. They also

began to develop distribution patterns that would

provide for interaction between the owls. The

guidelines incorporated the latest information

from the Oregon-Washington Interagency Wildlife

Committee.

Following a review of the approach to MMRs that

several Region 6 Forests were using it was

determined that some items needed clarification.

On April 16, 1984, this clarification and some

additional direction was sent to the Forests.

Emphasis was placed on habitat distribution as a

key to minimum viable populations. Criteria for

distance between spotted owl habitats had been

established. A requirement to connect three or

more habitats whenever possible was added.

Following this direction, the minimum viable

population goal for spotted owls increased from

399 pairs to 530 pairs.

The MMRs were developed over several months using

data from spotted owl research and the advice of

professional wildlife biologists and planners

from all levels of the Forest Service. A brief

review of the planning of the forests with

spotted owl habitat reveals the following:

1. All Forests are using a grid pattern as a

planning model.

2. A few (41) habitats will be managed for

timber over a long-term harvest plan.

3. Most (489) habitats will be dedicated to oldgrowth forest and will not be harvested so long

as they are suitable for spotted owls.

4. Of the 530 sites, 413 currently contain

enough old-growth forest to make them suitable

as spotted owl habitat.

5. And, 117 sites have potential as owl habitat

but are not currently suitable because of the age

of the timber. The particular age used as a

determining factor varies by forest but a forest

generally becomes suitable for owl habitat

between 140 and 170 years of age.

6. There are 374,417 acres of commercial forest

affected by this management or about 4 percent

of the commercial forest base of those Forests

involved. (This data is tentative and subject

to change during the planning process.)

Considerable refinement and expansion was done

to plan for spotted owl habitat management in

the final Regional guidelines. Following is a

summary of some of the guidelines:

$

1. The northern spotted owl will be considered

a "management indicator species" in Forest

planning.

2. To ensure that viable populations will be

maintained, habitat must be provided to support

at least a minimum number of reproductive

individuals, and that habitat must be well

distributed so these individuals can interact

with others in the planning area.

3. Each Forest is directed to:

A. Analyze and display the economic effects

of providing for a specified number of

spotted owls.

B. When additional spotted owls are

discovered, include these owls in the range

of alternatives considered in developing

Forest plans.

C. Incorporate management for spotted owls

into the planning process at those Forests

that discover owls subsequent to this

direction.

D. Establish new minimum population numbers

for those Forests where habitat is

determined incapable of meeting the assigned

numbers.

4. The modeling procedures must meet the

following criteria:

A. Be silviculturally attainable.

B. Be designed to ensure maintaining viable

populations of owls.

C. Provide for proper distribution.

D. Meet habitat needs as defined in the

proposed Spotted Owl Management Plan (March

6, 1981) and the Regional MMRs (February 9,

1983).

5. One of the following methods will be used to

model the effects on timber yields:

A. Dedicate the area to old growth.

B. Designate the area to management over an

extended rotation designed to meet habitat

needs.

C. Designate the area to uneven-aged timber &

management that meets habitat needs.

D. Designate the area to some combination

of the above systems or manage different

areas under different systems.

Y.

c

6. At least two Forest plan alternatives

relating to spotted owl management will be

8
evaluated. One alternative will evaluate the

Forest's share of the minimum viable population

for the Region and the second will evaluate the

minimum plus 30 percent. Other alternatives

will be considered where indicated to meet

-5 multiple-use objectives.

Following is a summary of events in the

T

evolution of management direction for spotted

owl habitat in Region 6.

A CHRONOLOGY OF PLANNING IN REGION 6

Pre-1973 Little interest in spotted owls.

Rapid loss of habitat.

1973

1976

1977

1978

%

1979

-4

1980

1981

1983

1984

Formation of Oregon Endangered Species

Task Force and recommendations from

task force to manage 300 acres around

known nest sites; rejection of

recommendations by Region 6.

Direction from Regional Forester to

protect known sites. Task force

recommends 400 sites be protected in

Oregon.

First spotted owl management plan for

Oregon; assignment of 290 pairs to

National Forests.

Direction by Regional Forester to meet

intent of plan for 290 pairs.

Region 6 spotted owl management

guidelines developed; revised Oregon

Interagency Spotted Owl Management

Plan.

National Forests protecting all known

nest sites and verifying location of

owls.

Revision of management plan. Issuance

of draft Regional plan; 263 pairs of

owls assigned to National Forests and

in Oregon and 112 to National Forests

in Washington.

Regional direction for determining

Minimum Management Requirements in

Forest planning.

Clarification and revision of 1983

direction; Forests establish new

minimums of 530 pairs; Regional guide

finalized (replaced document referred

to as Regional plan).

RESEARCH

Spotted owl habitat often consists of mature or

old-growth timber on highly productive sites

capable of producing up to 90,000 board feet Per

acre in a 60-year period. There is a lot of

interest in how that land is allocated.

Questions, that research can answer, about the

conflict between the requirements of the owl and

potential timber production have been identified:

How are old growth timber stands identified,

inventoried and properly classified?

What happens to old growth when it is put under

management?

What mix of old growth, mature, and other age

classes is acceptable to the owl?

What are the upper and lower acreage limits that

affect the suitability of the site for owl

habitat?

What is the upper limit on acceptable

disturbance before the site losses it habitat

capability?

What is a minimum viable population of spotted

owls and what is its distribution?

What are the dispersal rates and distances by

sex and age of the spotted owl?

SUMMARY

The spotted owl jumped from obscurity to

National prominence in a few years. The reason

for this is the owl's affinity for old-growth

timber along the west coast. Continued research

is needed to determine the allocation of spotted

owl habitat among the owl, other old-growth

dependent species, and timber production. State

and Federal agencies continue to plan these

allocations. Cooperation between the agencies,

private land owners, and persons with an

interest in the owl and its habitat is essential

if a balance between the timber productivity of

these sites and a stable population of owls is

to be achieved. The agencies involved are

seeking and using all available information in

planning for the future of these resources.

LITERATURE CITED

U.S. Department of Interior, Fish and Wildlife

Service. Threatened wildlife of the United

States. Resour. Publ. 114. Washington, D.C.:

U.S. Department of Interior, Fish and Wildlife

Service; 1973. 289 p.

9
INTRODUCTION

IMPLEMENTING A SPOTTED OWL MANAGEMENT PLAN:

THE GIFFORD PINCHOT NATIONAL FOREST EXPERIENCE

William C. Ruediger

ABSTRACT : Managers faced with implementing a spotted owl management plan

should anticipate the long-term realities of loss of habitat from natural

and human induced causes, the necessity of building in flexibility to

accommodate changes, the need to measure suitability of the actual habitat

and use by spotted owls prior to making land allocations, and the role of

monitoring.

Over the last 6 years the Gifford Pinchot

National Forest, Pacific Northwest Region, has

been in the process of developing a spotted owl

management plan. The objective of the plan is to

maintain spotted owls, and other species that

utilize or require mature or "old-growth forest

conditions,' throughout their existing range in

the Forest. During this period of change and

exchange of facts and philosophies, certain

realities have become evident and some

far-reaching and complex challenges have

surfaced. The conclusion is that the challenges

are growing each year and the options for solving

these challenges are decreasing. Decisions being

made today are going to dictate options and

success rates for tomorrow, and we cannot wait to

make these decisions. Perhaps by looking at the

experience in the Gifford Pinchot, other

WILLIAM C. RUEDIGER is a wildlife biologist, USDA

Forest Service, Gifford Pinchot National Forest,

Vancouver, WA.

biologists and managers can evaluate their

situations and make better decisions.

There are several critical elements land managers

and biologists should consider when developing

and implementing a spotted owl management plan.

These critical elements may have universal

application across the range of the spotted owl

or , on a broader perspective, they seem to apply

for any species being managed near minimum

population levels.

The key features of a spotted owl management plan

include:

1. The quantity of habitat provided.

2. The quality of habitat provided.

3. The distribution of habitat provided with

emphasis on key axis habitats which if lost could %

isolate geographic populations.

4. Demonstrated use by spotted owls

(verification).

5. The ability of the individual management

areas and the overall plan to absorb unforeseen

impacts.

:qr10
The following documents how these critical elements

have evolved from and affected the Gifford Pinchot

National Forest's spotted owl management program

between 1978 and 1984.

.h>

QUANTITY OF HABITAT

Both the number of spotted owl management areas

'g provided and the size of each area are important.

In 1978, the Gifford Pinchot National Forest was

providing 40 acres of habitat around each spotted

owl nest site. As only one nest site was known

then, the total area managed for spotted owls was

40 acres.

In 1979, the policy was changed to provide habitat

for 39 pairs of spotted owls. Each pair was

allotted 300 acres of old growth or, if this was

not present, mature habitat in the Douglasfir/hemlock vegetative zone. The basis for 300

acres of habitat for each pair was the Oregon

Spotted Owl Management Plan. l/ Whenever

possible, management areas where spotted owls were

known to exist were given priority over adjacent

areas without known pairs. The total area needed

to sustain this population level was 11,700 acres.

In 1980, the Gifford Pinchot National Forest made a

decision that all spotted owl management areas

would be inventoried prior to selection to evaluate

habitat suitability. During this time, Mount St.

Helens erupted and destroyed approximately 24,000

acres of old growth and mature Douglas-fir/ hemlock

.2c type forest, much of it known to contain spotted

owls. A new spotted owl management strategy was

prepared, this time utilizing 45 pairs of spotted

owls and 540 acres of habitat per pair (300 acre

-9 nesting core plus three 80-acre foraging areas).

The basis for using this criteria was the Oregon

Interagency Spotted Owl Management Plan. 2/ The

total area necessary to sustain this population was

24,300 acres.

The Oregon Interagency Spotted Owl Management Plan

was revised in 1981, 3/ reflecting the

then-current consensus that 1,000 acres of

old-growth habitat was necessary for each pair. In

1982 the Forest told Ranger Districts that 1,000

acres of habitat would be maintained for all pairs

identified in the Spotted Owl Management Plan, and

that 1,000 acres would be maintained for all new

spotted owl pairs located

l/ Oregon Department of Fish and Wildlife. 1978.

Spotted owl work group meeting, plan on file at the

NW Regional Office, Corvallis, OR.

2/ USDA Forest Service. 1984. Regional Guide for

-4.. the Pacific Northwest Region. Appendix C, p.

c-5/6/7. On file at USDA Forest Service, Region

Six, 319 S.W. Pine, P.O. Box 3623, Portland, OR.

,

"Z

3/ USDA Forest Service. 1984. Regional Guide for

the Pacific Northwest Region. Appendix F, p.

F-2/3/4. On file at USDA Forest Service Region

Six, 319 S.W. Pine, P.O. Box 3623, Portland, OR.

until the Forest's plan was completed. The

number of acres necessary to sustain the spotted

owls identified in the Gifford Pinchot National

Forest Spotted Owl Management Plan and the Mount

St. Helens Land Management Plan was 47,000

acres. An additional 7,000 acres received

temporary reprieve from timber harvesting as

"pair protection areas" pending final disposition

in the Forest's plan. The total acreage

receiving management emphasis for spotted owls

was 54,000 acres.

The situation as of 1984 is that there are now 14

"pair protection areas." The 47 pairs in the

Gifford Pinchot Spotted Owl Management Plan and

Mount St. Helens Land Management Plan are also

being provided for, for a total short-term

commitment of 61,000 acres.

There are several scenarios that could be

provided for the future, but let me provide what

I consider a minimal approach for the Gifford

Pinchot National Forest. Recent analysis

suggests that the lowest number of spotted owls

that could be managed for over the long term,

with a reasonable amount of risk, is

approximately 52 pairs. At this level, there

would be 10 habitats providing flexibility for

situations described later in this paper.

There are two ways spotted owl habitat could be

managed. The first option is referred to as

"dedicated", whereby suitable areas of 1,000

acres would be identified and preserved. The

total area necessary to sustain 52 pairs under

this type of management would be 52,000 acres,

some of which is already being preserved under

such allocations as "wilderness" and *national

monument".

The second option would consist of managing

approximately 2,400 acres under a 240-year

rotation to sustain 1,000 acres of habitat

suitable for one spotted owl pair. If 80 percent

of the spotted owl management areas were managed

with an extended rotation and 20 percent managed

as dedicated (in wilderness or national monument

status), the acreage necessary to sustain 52

spotted owls would be 110,800 acres.

QUALITY OF HABITAT

Occupied spotted owl management areas were

measured in the Gifford Pinchot National Forest

and the following stand characteristics were

observed:

1. Twenty to 40 large trees per acre (30-in.

diameter at breast height (d.b.h.) or larger).

2. Eight or more large snags per acre (20-in.

d.b.h. or larger).

3. Twelve or more downed logs per acre (12-in.

d.b.h. or larger).

4. Multistoried stands with at least 80 percent

canopy closure.

In 1980, the Forest planned to inventory habitat

in all areas being considered for spotted owl

management. The eruption of Mount St. Helens

1l
made inventorying impossible over much of the

Forest; however, 23 areas were evaluated. Of the

23 areas inventoried, 3 (13 percent) were

subsequently determined to be unsuitable because

they lacked one or more of the previously

described habitat components. The three areas

considered unsuitable were replaced with more

suitable areas nearby.

Between 1981 and 1984, approximately 25

additional potential habitat areas have been

inventoried. Five (20 percent) of these were

subsequently determined to be unsuitable and

replaced with suitable areas. These areas had

preliminary evaluations consisting of aerial

photograph reviews and nonmeasurement ground

reconnaissance.

Managers who have not measured actual spotted owl

habitat parameters can likely assume that 15-20

percent of the areas being considered or managed

as habitat may not meet minimum standards.

USE BY SPOTTED OWLS

A significant portion of management areas judged

to be suitable habitat (even after a habitat

inventory) may not be used by spotted owls. For

example, in the Gifford Pinchot National Forest

approximately 20 percent of the spotted owl

management areas have either had to be replaced

because use by owls could not be confirmed, or

the areas continue to be managed as habitat

without owls. If habitat inventories had not

been the basis for locating management areas, an

estimated 40 percent of the spotted owl

management areas selected would not have been

suitable.

Spotted owl management plans that are developed

with little or no information on habitat or use

can be expected to go through major revisions, or

they may not sustain expected population levels.

DISTRIBUTION OF HABITAT

Distribution strategies must consider

availability and suitability of habitat, home

range and territory sizes, dispersal distances,

and other pertinent behavioral and environmental

factors.

In the Gifford Pinchot National Forest, habitat

availability has necessitated managing spotted

owls above the densities that could be sustained

if habitat were uniformly distributed.

Theoretically, if my mathematics are close,

spotted owls could be managed at one pair per

40,000-42,000 acres, using maximum distances

provided in the revised Oregon Interagency

Spotted Owl Management Plan. Estimated minimum

densities in the Gifford Pinchot National Forest

are one pair per 30,000 acres. This density is

about 25 percent greater than the theoretical

minimum and results from the existing

distribution of suitable habitat in the Forest.

When occupancy by spotted owls (verification)

becomes a criterion for habitat suitability, many

old-growth areas may be excluded. Each

additional criterion further limits the selection

of choices and will tend to increase the density

of habitats managed. *-

Intermingled private and public land ownerships

can also contribute to distribution, management,

and other resource impacts. This is a

significant problem on many Forest Service and

i

Bureau of Land Management lands. Intermingled

ownerships commonly create at least three

problems for the land manager. First, the impact

on timber resources is increased for the managing

agency if all habitat requirements must be

supported on half of the available land area,

which is a common situation where there is

railroad-ceded lands. Second, intermingled

ownership may increase the density of owls that

must be managed because of restricted

availability or suitability of areas that can be

selected. Third, management of habitat on

federal lands can be hampered by factors such as

blowdown and fragmentation, which can result from

large areas cutover on adjacent lands.

ABILITY OF A SPOTTED OWL MANAGEMENT PLAN TO

ABSORB UNFORESEEN IMPACTS

The experiences I have had over a relatively

short period of time have convinced me that an

important part of a spotted owl management plan

is its provisions for absorbing unforeseen :fl.

impacts such as natural disasters, land ownership

or land use changes, and management mistakes.

These impacts can be catastrophic, as in the case

of the eruption of Mount St. Helens: more often

they are subtle and cumulative.

F

The following are examples from the Gifford

Pinchot National Forest of how these impacts can

be widespread and significant, even over the

relatively short timespan of 5 years.

Natural Disasters:

1. The eruption of Mount St. Helens eliminated

approximately 25,000 acres of mature and

old-growth forests on National Forest lands known

to contain a high density of spotted owls.

2. The Christmas Day windstorm in 1983 caused

215 acres of blowdown in six spotted owl

management areas, including 75 acres in one core

area. This resulted in having to make

adjustments in five areas, combine two other

management areas into one, and relocate one

management area. Blowdown appeared greatest

adjacent to harvest units, particularly in

locations where habitat had already been

fragmented by timber harvesting.

Land Exchanges:

1. Land exchanges south and west of Mount St.

Helens resulted in relocation of two management

areas. The land ownership pattern was

intermingled.

12
2. Land exchanges to the south and west of Mount

Rainier National Park will likely result in the

loss of one or more spotted owl management

areas. The land ownership pattern is

3

intermingled.

Management Problems:

(3

An escaped slash fire in 1979 resulted in 1,200

acres of old-growth habitat being burned. A

spotted owl management area tentatively planned

for this area was moved to another, less suitable

area.

SUMMARY

Viability and flexibility of spotted owl

management plans and strategies will depend

largely on:

1. Identifying suitable habitat based on habitat

inventory data, verification of spotted owls and

evidence of breeding success. If possible, radio

telemetry should be used to focus on habitat used

by owls in contrast to habitat that may appear

suitable but does not receive use.

2. Providing management areas that are larger

than the minimum necessary to maintain owls so

there is flexibility to adjust for spatial needs

and allow for habitat attrition. Reliance on

minimum-sized management areas (1,000 acres)

carries a high risk.

3. Considering distribution and land ownership

patterns to identify key axis areas where

geographic populations could be isolated if

habitat were lost.

4. Providing an adequate number of management

areas so that viability is maintained even if

several areas are lost. Emphasis for additional

areas should be placed at key axis locations to

ensure distribution criteria are met over time.

Management plans or strategies that rely on

minimum population levels should be considered

high risks.

5. Diligent monitoring of critical factors such

as dispersal of young, mortality rates, breeding

success, spatial and habitat requirements, and

changes in habitat caused by natural and human

induced causes.

13
OLYMPIC NATIONAL FOREST SPOTTED OWL HABITAT MANAGEMENT:

TRANSLATING EVOLVING MANAGEMENT GUIDELINES INTO ACTIONS

Maureen A. Beckstead

ABSTRACT: Significant progress has been made in identifying the distribution,

abundance, and habitat of spotted owls in the Olympic National Forest. Implementation of the Spotted Owl Management Plan has been complex due to the

geography of the Olympic Peninsula, the vagaries of spotted owl behavior, and

other resource conflicts. The Olympic National Forest is committed to a more

complete, site-specific knowledge of spotted owl habitat use and continues to

gather data through monitoring to help refine future management regimes.

INTRODUCTION

It is a task of personnel in Supervisors' Offices

of National Forests to identify and clarify, to

define and refine management direction and guidelines, and to oversee inclusion of the guidelines

in land management planning and field operations.

It is a task of personnel stationed at Ranger

Districts to interpret and employ management

direction and guidelines in project planning and

field operations. These tasks are necessarily

complex because they are often concurrent, usually

iterative, and always interactive.

The implementation of spotted owl habitat management direction and guidelines has been complicated

by the fact that this direction has been continually evolving, as has direction for development

of Forest Land Management Plans. This evolution

will continue as research and monitoring identify

new or more refined information and as Forest

Land Management Plans are completed, amended, and

revised.

Direction to the Olympic National Forest

(Olympic) to manage northern spotted owl habitat

is less than 5 years old. Early direction specified that this Forest would maintain a specific

number of "known" spotted owl habitats and guidelines were developed that indicated the size and

distribution of suitable habitat within each

Spotted Owl Management Area (SOMA). Following

several changes, later direction specified size

and distribution of suitable habitat within SOMAs, k

minimum and maximum distances between SOMAs, and

a distribution that would allow owls in any one

SOMA to disperse to at least three other SOMAs.

MAUREEN A. BECKSTEAD, former Olympic National Implementation of management direction and guideForest wildlife biologist, is Landowner Relations lines for size and distribution of habitats is

Program Manager for the Department of Game, complicated by certain geographic features parOlympia, WA. titular to the Olympic. Major features include:

14
probable geographic isolation from suitable habitat in the Cascade Range; size and shape of lands

managed by the Olympic; previous land management

and fire history of the Olympic and adjacent landowners.

Add to these features the facts that little information is available regarding spotted owls or

habitats on adjacent lands and that spotted owl

G

behavior appears to vary from year to year and

area by area. Implementation of a spotted owl

management plan may have to employ large doses of

"best professional judgment" to meet the intent,

if not always the letter, of management direction.

The purpose of this paper is to discuss the techniques and procedures used, the progress to date,

and the difficulties encountered in identifying

and planning for SOMAs in the Olympic. Also important to discuss is the need for continuing to

refine techniques, knowledge, and management

direction through monitoring, evaluation, and revision. Because direction, procedures, difficulties, and progress were evolving at the same time,

I have chosen a chronological format for this discussion for the sake of clarity.

IMPLEMENTATION

Ancient History Through 1977

The earliest direction received by the Olympic

stressed inventory of spotted owls. All sightings,

& nest locations, and acres surveyed were to be reported to the Pacific Northwest Regional Office by

July 1977. Interim to the completion of a Spotted

Owl Management Plan by the Oregon Endangered Spefl7

cies Task Force, habitat diversity was to be maintained. More specifically, a complete range of

successional stages was to be retained in areas of

8,000 to 20,000 acres.

To this time, no inventory of spotted owls had

been performed in the Olympic b Forest Service

personnel. Howard R. Postovit conducted the PI

first survey in Washington in 1976. Several of

his survey routes occurred in Olympic National

Forest and in Olympic National Park.

Postovit surveyed areas of unharvested old-growth

forest, mosaics of old-growth and second-growth

stands, and uniform second growth. These were divided into five classes by proportion of old

growth and 30 routes were randomly selected for

survey in each class. Routeswalked were 2

1/2 miles

long; each route was walked twice while calling

owls at 164-foot intervals. If an owl response

was heard, Postovit moved three-quarters of a mile

before calling again to avoid calling the same

bird. Data collected within 327 feet of each owl

-3'

1/ Unpublished report, 1977, "A Survey of the

Spotted Owl in Northwest Washington," by Howard R.

Postovit, National Forest Products Association,

1619 Massachusetts Avenue, N.W., Washington, DC

20036

location included elevation, topography, tree

species, canopy density, approximate stand age,

average diameter at breast height (d.b.h.) of

overstory trees, and forest class.

Fourteen owls were located at 13 sites on the

Olympic Peninsula and 8 owls were located at 7

sites in the Cascade Range. Almost all locations

were in old growth; the majority of surrounding

areas were more than 66 percent old-growth forest.

On the Olympic Peninsula, 9 owls were found on

National Forest lands and 5 owls on National Park

land. Average slope was 55 percent; all owls

were located on western and northeast slopes;

elevation ranged from 752 to 3,188 feet on the

west side of the Peninsula and from 1,488 to

2,747 feet on the northeast side.

Survey, 1978

William Brown, Jr., Forest Wildlife Biologist for

the Olympic, contracted with Ken Dzinbal, Oregon

State University, to conduct a spotted owl survey.

The survey was designed to determine the existing

geographic range of spotted owls in the Olympic,

to provide preliminary information on habitat

preferences and owl density, and to refine inventory techniques for future use.

Dzinbal, usually accompanied by Ranger District

personnel, ran 417 miles of road transects in

over 40,000 acres of suitable habitat; i.e.,

areas that contained predominantly old growth

and that were under 4,000 feet in elevation.

Nonroaded pristine old growth and areas predominantly in younger stands were not surveyed for

practical reasons.

Owls were located by calling at night for 1 minute every one-quarter mile along a road transect.

If a response was received, the observer moved 1

mile before calling again. Data collected at

each response location or sighting included aspect, percent slope, elevation, time, percent

cloud cover, moon phase, precipitation, wind

speed, and temperature.

The survey resulted in a total of 51 responses

and 3 sightings, of which 13 may have been

male/female pairs, at 38 separate locations. Response locations indicated spotted owl use predominated at midelevation ranges on moderately

steep slopes on northwest or southeast aspects.

Owl use was different on west and east sides of

the Olympic. On the east side, locations of owls

averaged 2,750 feet in elevation and occurred

only on south, southwest, and southeast aspects.

On the west side, locations averaged 1,900 feet

in elevation, and 70 percent occurred on north,

northwest, and northeast aspects.

Density of owls, based on responses and sightings,

were one owl (pair) per 8.9 miles of road surveyed. Area density was calculated from clusters

of responses representing three or more owls

(pairs). Area densities ranged from one owl

(pair) per 1.96 square miles to one owl (pair)

per 4.17 square miles. The assumption in 1978

was that spotted owls were rarely known to live

separately so that each response was considered

15
a pair location. More recent survey and research

have cast doubt on this assumption.

Hiatus, 1979-1980

Though management direction and guidelines were

evolving rapidly during this period, activity at

the field level consisted of documenting accidental encounters with spotted owls and some nonstandardized surveying of proposed timber sale areas.

In 1979, for the first time, the State of Washington joined the spotted owl planning process and

the Oregon-Washington Interagency Wildlife Committee revised the Spotted Owl Management Plan (SOMP)

During 1980, a USDA Forest Service task force developed a process to determine various levels of

viable spotted owl populations; it was assumed

that all owls in Oregon and Washington were one

interbreeding population. The Regional Forester

adopted the SOMP and forwarded direction to the

Olympic to maintain at least 17 SOMAs as a tentative, interim allocation. The Olympic National

Forest Plan was to evaluate various alternative

management levels. SOMAs were to encompass 1,200

acres of "known" spotted owl habitat and include

a 300-acre contiguous old-growth core around a

nesting site, plus at least three 80-acre feeding-perch patches nearby in order to implement

the SOMP. The Olympic was directed to designate

confirmed or suitable SOMAs by July 1981.

Standards for confirming SOMAs and verifying core

nesting areas were also developed in 1980.2/ Confirmation of general SOMA occupancy consisted of

two or more visual observations or auditory responses of spotted owls in approximately the same

area, 72 or more hours apart, anytime throughout

the year. Verification of a core area must be

made during the period from March 1 to August 31

and consist of one of the following: one or more

visual observation or auditory response of an

adult male and female within the same one-quarter

square mile area; three or more visual observations or auditory responses of an adult bird in

the same one-quarter square mile area, 72 or more

hours apart; or location of a nest or recently

fledged young-of-the-year birds.

Habitat for all known pairs was to maintained

until the Olympic verified its minimum number of

SOMAS. Further, once a SOMA was confirmed, no

habitat modification was to occur until the core

area was verified. Once the minimum number of

SOMAs were verified, Forests were encouraged to

maintain habitat for other known pairs to provide

for alternative planning levels.

Implementation and Planning, 1981

The SOMP was revised in 1981 and the Olympic received direction to establish SOMAs containing a

300-acre core area with an additional 700 acres

2

/ Horn, Kirk M, 1980, Information on file at the

USDA Forest Service, Pacific Northwest Region,

P.O. Box 3623, Portland, OR. 97208, 2 p.

of old growth within 11/2 miles. These SOMAs were

to be distributed no more than 6 or 12 miles

apart depending on whether they contained a

single pair of owls or multiple pairs. Singlepair SOMAs were acceptable only to meet distribution requirements or where remnant habitat

existed. Other direction continued, including 3

the prohibition on habitat modification except

that, now, timber sold previous to October 1980

was exempt and available for harvest.

F

I was transferred to the Forest Wildlife Biologist position in 1981, though I had been working

on the Olympic Forest Plan during the previous

year. It was already obvious that geography and

topography were going to make implementation of

the SOMP difficult, at best. The Olympic resembles an elongated doughnut, broken on the

west side by extensive areas of State and Indian

reservation lands and on the north by private

lands that surround the Olympic National Park.

Width of the Olympic in most areas is 12 miles

or less and rarely exceeds 15 miles. Because of

previous, intensive and extensive fire history,

as well as a history of lowland timber harvesting, large areas were void of suitable spotted

owl habitat, as defined by the Regional Office.

Identifying potential SOMAs to provide well-distributed habitat throughout the historic range

in the Olympic planning area was impossible. No

SOMAs were yet verified, but managing only 17

potential areas out of over 40 response and observation locations caused them to be strung out

like beads on a necklace at distances exceeding

management direction. Previous inventory of

owls and habitat indicated that clusters of owls

for multiple-pair SOMAs were extremely rare except on one Ranger District, so that a 6-mile

distribution of habitats was the norm. Because

the previous survey was conducted only in roaded

areas, most potential SOMAs were in conflict

with existing or proposed timber sales and were

often already fragmented to some degree.

Survey and attempts at verification of SOMAs

were reinitiated in 1981. The Forest Supervisor's direction emphasized (1) survey of proposed timber sale areas to comply with the process required by the National Environmental

Policy Act; (2) survey of roadless areas or

lands dedicated to purposes other than timber

management to reduce resource conflicts; and

(3) reinventory and verification of areas with

a previous owl history.

Surveys were conducted at night between March

and September using recorded spotted owl calls

amplified from a cassette tape player. Surveyors

included personnel from any and every resource

area in District and Supervisor's Offices. Crews

of two or more drove a predetermined route,

stopping every one-quarter mile and calling

every few seconds for 5 to 10 minutes at each .estop. On trail routes, calls were played every

few minutes. Calling generally began 1 hour

after sunset and lasted about 4 hours. Response

locations or sightings were mapped; time,

weather, and comments were recorded.

16
Although 41 responses were received during 332

hours of survey, which compared favorably to 51

responses in 276 hours in 1978 with many locations repeats from 1978, no SOMAs were either

verified or confirmed to the regional standards

?k described above. It was noted in 1981 that moving 1 mile from a response or sighting was not

always enough, as some observers were followed

by owls for several miles, particularly early in

'ir the breeding season. Also, about half of the

areas where owls were located in 1978 that were

checked in 1981 did not produce owl responses.

Implementation and Planning, 1982

The Olympic issued direction that verification of

at least 17 SOMAs was a high priority so that

Forest Plan development could proceed based on

site-specific information. The Olympic also

agreed to participate in the L-year spotted owl

census organized by the Department of Game,

however, and was committed to run eight census

routes in the Forest and Park. Funding for these

activities was minimal so verification efforts

were also limited.

Details regarding procedures used for the State

census routes are presented elsewhere

(Allen and Brewer 1985). Efforts at verification

followed regional standards. Though 40 owl responses were received in 442 hours of survey, only

three SOMAs were verified on two Ranger Districts

by the end of the season. Two SOMAs were within

3 miles of one another, further complicating the

i2- distribution problem. Many response locations

repeated those of either 1978 or 1981, or both,

but some were new, and again resurvey of old locations produced responses only about half of the

9 time. It was also apparent, through annual responses, that in at least one Ranger District owls

were using habitat not considered "suitable" by

Regional Office definition.

To proceed with the development of the Olympic

Forest Plan , potential SOMAs were allocated to

each District according to the following prioritized criteria:

1. SOMAs already verified;

2. Potential SOMAs with a history of previous

responses or sightings;

3. Potential SOMAs with no history of occupation,

that were needed to meet distribution criteria for

suitable habitat, but with few resource conflicts;

and

4. Potential SOMAs with no history of occupation

that were needed to meet distribution criteria,

but either had resource conflicts or habitat not

considered immediately suitable.

These potential SOMAs were entered into the Olympic's Total Resource Inventory System (TRI System),

4% which served as the data base for the Forest Plan

and the automated mapping system, R-2 Map. From

these systems, detailed information could be retrieved for each potential SOMA; information that

-y included number of acres assigned inside and outside the core, elevation, aspect, vegetative ecoclass, stand tree size, and stand year of origin.

Where there had been any silvicultural exams or

inventory plots within a SOMA, data also included

percent of area in trees, shrubs or grass-forb

stages, major species, and a history of any management activity or direction.

Following allocation, the extent of conflict with

other resource activities became more apparent.

For instance, all three SOMAs verified in 1982

contained timber sales already sold as well as

proposed sales. One SOMA had timber units sold

prior to October 1980 (which were exempt) in the

core, including the suspected nest tree. Locations of a radio-collared male from this SOMA

showed him to be repeatedly using areas scheduled

for harvest within 1 to 2 years. The Olympic is

presently in the expensive and time-consuming

process of modifying several sales to provide

protection for areas of owl use.

The need for continuing refinement and interpretation of management direction coupled with large

doses of "best professional judgment" arose along

with the immediate and ongoing requests for boundary changes to accommodate other resource needs.

A careful balance of priorities was needed to resolve resource conflicts that included theoretical knowledge of life history and habitat use of

spotted owls weighed against the ability of managers to accomplish their timber managment activities elsewhere.

Semi-finally, 1983

The Forest Supervisor for the Olympic issued

direction to Ranger Districts to complete verification of their minimum allocation of SOMAs plus

one additional area by the end of the 1983 season.

Again, the Forest's funding was minimal so that

only half of the State's census routes were completed, as emphasis was placed on verification.

This direction stemmed from the recognition that

planning based on potential SOMAs was a major

factor in the difficulties described previously,

and that a site-specific knowledge of spotted

owl use would lend more credibility to the

decision-making process.

During an intensive effort involving 1,577 hours

of field work, of which one-third was volunteered

77 responses or sightings were recorded. Fourteen SOMAs were confirmed and nine core areas

verified within them. Though the total allocation of 17 SOMAs had been confirmed, the requirements for distribution of habitat could not be

met because all but two seemed to be single-paired

and because of the geography of the Forest.

Other possible anomalies appeared with the confirmation of two SOMAs in habitat previously

considered "unsuitable)"' one of which produced

two fledglings. Special attention was given to

this SOMA due to the paucity of old growth within

11/2 miles of the nesting area. Much of the Ranger

District, including the SOMA area, includes 90-

year-old, or younger, stagnated stands ranging

from 5,000 to 20,000 stems per acre. Some areas,

however, contained old-growth elements such as

interspersed larger trees and snags. In an

effort to determine the appropriate size and

shape of this SOMA, an attempt to determine the

17
prey base, prey base density, and habitat use by

the owls was begun. Department of Game captured,

radio-collared, and monitored habitat use of the

two fledglings through mid-1984, though the

fledglings soon dispersed from their natal area.

District personnel and I collected eight pellets

from the fledgling roost area. These were analyzed by Murray Johnson, University of Puget Sound,

and were found to include nine northern flying

squirrels, two red-backed voles, and one adult and

three immature bushy-tailed woodrats. I also

observed a cached (partial) snowshoe hare while

collecting pellets. Funds were requested to

determine prey base density in order to estimate

the amount of habitat necessary to support the

dietary needs of an adult pair and two fledgling

spotted owls.

Because of these anomalies, distribution difficulties, erratic occupancy of specific areas, and

the long distances apparently traveled by curious,

defending, or dispersing spotted owls, the Olympic

in concert with the Mt. Baker-Snoqualmie and Gifford Pinchot National Forests cooperatively developed a SOMA monitoring plan with Forest Service

research and the Washington State Department of

Game. This plan is described in a paper by

Carey and Ruggiero (1985).

Meanwhile, regional direction was refined and made

more specific, and issued as minimum management

requirements for establishing viable populations

of spotted owls in the Forest planning process.

This direction was used to establish the latest

confirmed and verified SOMAs and core areas in

the Forest Plan data base during the planning

"pause" which followed the Ninth Circuit Court of

Appeal's decision regarding evaluation of RARE II

areas.

Existing Situation, 1984

A summary of the Olympic's data on spotted owl

habitat use as of early 1984, included a total of

209 owl responses or sightings at 48 locations.

Locations were considered "separate" if they were

2 to 3 miles from any other location. Of these

locations, 17 had been confirmed as SOMAs and 12

core areas were verified. Breeding pairs or

fledglings had been observed in three of these

SOMAS. Field work involved 2,627 hours, which

was estimated to be one-third to one-half of the

total expended on implementation of the SOMP.

By including all 48 known locations and all potential suitable habitat on one map, it was apparent

that there were still some weak links in the geographical distribution of spotted owls and habitats

on the Olympic's east and south sides. These were

due primarily to previous fire history on the east

side and intensive and extensive timber harvest on

the south side. I had repeatedly expressed concern to the Regional Office biologists that the

probability existed that spotted owls on the Olympic Peninsula were genetically isolated from those

occuring in the Cascade Range, and that this isolation may have begun in the very early 1900's

when the lowlands in the Puget Trough were logged

off within a 30- to 40-year period. An analysis

of the risk involved in managing 17 habitats for

lympic following the proceindicated that this population, viewed in isolation, could become 50 percent inbred in only a few generations.

Recognizing that the Peninsula subpopulation of

spotted owls included those on adjacent lands,

3

the Olympic National Park was queried for any

spotted owl use data and an estimate of the amount

and location of potentially suitable habitat.

Park personnel had very limited data and declined P

to make an estimate of habitat. I polled seven

Forest Service and State biologists for an estimate of either spotted owl density or suitable

habitat in the Park; estimates ranged from 42 to

109 pair. Risk analysis was again performed

(including potential Park owls), which indicated

long-term evolutionary fitness was unlikely for

an isolated Olympic Peninsula subpopulation. Department of Game had data on three owl areas on

adjacent Department of Natural Resources lands,

but to date there has been no State agreement to

manage spotted owl habitat.

Direction from the Regional Office was received

in April and included recognition of the probable

isolation of spotted owls on the Olympic Peninsula. It was suggested that, in the absence of

protection for habitats linking the Olympic Peninsula and the Cascade Range, the Olympic subpopulation might be periodically enhanced through transplants in cooperation with Department of Game.

Other direction stated that the number of SOMAs

to be managed, at a minimum, would be determined

by an appropriate distribution of habitats rather

than by a number of owl pairs calculated to pro3

vide genetic viability.

The new distribution requiremeuts were mapped and

SOMAs located such that any one SOMA was distributed within dispersal distance of at least three

others, and so that no large area was void of

habitat. The Olympic, being too narrow to accommodate this distribution, and having all but one

SOMA distributed at 6 miles because of the

single-pair situation, added potential Park habitats to the 28 or 30 needed for distribution on

National Forest lands. These Park habitats were

added where necessary to tie Olympic lands, fragmented by other landowners or unsuitable habitats

into one continuous distribution. Suitable Park

lands were taken from a map generated by remote

sensing data, which included age and elevational

criteria; none of these habitats have yet been

examined on the ground or inventoried for owls.

During the 1984 field season, funds were requested to census the prey base in the stagnated

timber stands within verified SOMAs. During

monitoring, spotted owls were located in all 11

SOMAs evaluated, thereby validating procedures

used to inventory and confirm these areas. Owls

B

3/ Contribution to Forest Service Handbook, FSH,

2609.14, draft November 25, 1983, Chapter 5.7,

Viable Population Risk Analysis, 34 p., by

H. Salwasser.

18
appeared to be spending as much time outside designated SOMAs as within, however, and some owls

could not be located in the SOMA until late August

after the breeding season. This preliminary information indicates the state of our imperfect

e

knowledge of spotted owl habitats and habitat use.

TIPS FOR NEW PROGRAMS

There are a few hints I can provide to those contemplating the start of a program to manage

spotted owls, or perhaps any species about which

relatively little is understood:

1. Count on a long-term project. Identify and

try to secure funding and personnel for a commitment of several years.

2. Concentrate surveys early in the breeding

season. Spotted owls appear most territorial

(responsive) before their young have fledged.

3. Don't waste your time. Visiting "perfect"

habitat more than three to five times in a season

appears to be nonproductive, though it should be

visited in consecutive seasons and during the

winter before being abandoned.

4. Recognize that suitable habitat is that which

is occupied by spotted owls, not that which meets

a standardized definition. Establishing habitat

management areas in a generalized distribution

pattern, then checking them for use causes constant readjustment and wastes time. General survey should be followed by habitat analysis, then

future surveys refined to reflect such data.

t- 5. A crew on contract is easier to standardize

and supervise. I found that, in the Olympic, the

*contract crew had a response rate per unit time

spent of one response per 5 hours of survey; crews

q

of various changing Forest Service personnel

achieved one response per 9 hours of survey; and

a combination of in-house personnel plus one-third

volunteers produced one response per 21 hours of

survey.

6. Lack of owl response does not necessarily indicate that owls aren't there. Responsiveness

appears linked to the technique of the caller,

weather, time of day and year, individual differences, number of times previously called, phase

of the moon, and whether or not it's Thursday.

7. When managing a species at low population

levels, where viability is a concern, supply the

best habitat available. Marginal habitat may be

only periodically occupied or may not be able to

support a breeding pair plus young.

8. Avoid conflicting resource uses, such as timber harvest, within SOMAs even though more than

sufficient habitat is available. Ongoing monitoring will continue to refine spotted owl habitat

use, and at low population levels, use should define habitat.

4 FUTURE NEEDS

The Olympic has defined its needs for more information through participation in the cooperative

45 SOMA monitoring study (Carey and Ruggiero 1985).

Additionally, information is being gathered on

specific habitat use by adult owls in stagnated

timber stands to define the SOMA parameters for

these anomalous situations. It would also be

prudent to examine the suitability of Park lands

and conduct a survey of spotted owls in habitats

that were selected to geographically ensure a

continuous distribution throughout the owls'

range. Managing owls near minimum population

levels allows little margin for error; assumptions regarding suitability and occupancy of

several habitats imposes a very high risk.

Several years of observation and preliminary monitoring data indicate a need for more specific information regarding differences in "winter range"

vs. "summer range" use by owls, differences in

male vs. female use of the home range during nonbreeding years, home range size of fragmented

SOMAS vs. contiguous ones, reproductive strategy,

and fledgling survival. These require research

efforts beyond the scope of an individual Forest

to purse.

Finally, there is a continuing and future need

for flexibility in management direction. Direction and guidelines need to be more immediately

responsive to new or site-specific data in order

for habitat to be managed to maintain pairs of

spotted owls. Presently, habitats are assigned

to owls and they must fit within those or perish.

With continuing monitoring and refinement of data

on habitat use and spotted owl biology, the opportunity exists to manage habitats selected by the

owls.

SUMMARY

Information on spotted owl distribution, density,

biology, and habitat use has been collected in

the State of Washington for only a few years. Imperfect knowledge coupled with the commitment to

maintain viable populations of this species, considered threatened in the State, caused the Regional Forester to adopt habitat management guidelines and issue direction for implementation of

the SOMP. This direction has been revised or refined nearly annually since 1977, but throughout,

has been highly specific and based on research

conducted, largely, in the forests of western

Oregon.

Implementation of management guidelines and direction was accomplished through the coordinated, interactive efforts of personnel from many resource

disciplines at both the Supervisor's and Ranger

District offices. Though significant progress

has been made in identifying the distribution,

abundance, and habitats of spotted owls in the

Olympic, implementation of the SOMP was made complex due to the peculiar geography of the Peninsula, the vagaries of spotted owl behavior, and

other resource conflicts.

The Olympic is committed to more complete,

site-specific knowledge of spotted owl habitat

use and continues to gather data through monitoring and administrative studies. The expectation

is that management direction in the future will

be flexible and responsible to new information,

for after all,

19
The ultimate result must be that we

maintain viable populations of spotted

owls, over time, such that we prevent

the need for Federal listing.

R. E. Worthington

Regional Forester

October 28, 1980

LITERATURE

Allen, Harriet; Brewer, Larry W. A review of

current northern spotted owl (Strix occidentalis

caurina) research in Washington State. In:

Gutiérrez, Ralph J.; Carey, Andrew B., tech.

eds. Ecology and management of the spotted owl

in the Pacific Northwest. Gen. Tech. Rep. PNW185. Portland, OR: U.S. Department of Agriculture,' Forest Service, Pacific Northwest Forest

and Range Experiment Station; 1985; 55-57.

Carey, Andrew B; Ruggiero, Leonard F. Spotted

owl management: meeting NFMA requirements

through monitoring. In: Gutiérrez, Ralph J.;

Carey, Andrew B., tech. eds. Ecology and management of the spotted owl in the Pacific Northwest. Gen. Tech. Rep. PNW-185. Portland, OR: Q

U.S. Department of Agriculture, Forest Service,

Pacific Northwest Forest and Range Experiment

Station; 1985: 34-38.

F

20
MANAGEMENT OF SPOTTED OWLS BY THE CALIFORNIA DEPARTMENT OF FISH AND GAME

Gordon I. Gould, Jr.

ABSTRACT: The California Department of Fish and Game must maintain populations of spotted owls for the intrinsic and ecological values of the owls.

The Department performs this job through a coordinated effort with land

management agencies to protect the old-growth and mature forest habitat required by the owl. Commercial logging dramatically reduces this habitat

and jeopardizes the species' existence. Problems in current land management planning are discussed and research needed to improve management is

identified. 

INTRODUCTION

The California Department of Fish and Game

(CDF&G) is charged with the conservation of all

wildlife within the State, including species that

are not harvested (Section 1801, Fish and Game

Code). This specific legislative mandate calls

for maintaining all species of wildlife and their

habitat (1) for the use and enjoyment by all

citizens of the state; (2) for the intrinsic and

ecological values that all species have; and (3)

for aesthetic, educational and other nonconsumptive uses. Management for species that are not

used consumptively (15 species of owls and 622

species of other birds and mammals) centers

around habitat preservation.

In 1970, the California legislature passed the

Endangered Species Act, recognizing that destruction of wildlife habitat. reduction in the

amounts of certain types of habitat, and severe

modification of many natural environments were

r, endangering many species, or subspecies, of

native wildlife.

2-4d GORDON I. GOULD, JR., is a Nongame Wildlife

Biologist for the California Department of Fish

and Game, Sacramento.

Subsequently, CDF&G's management activities included monitoring populations, determining habitat requirements, preserving particular habitats,

and assessing other land management agencies in

their management of land and other resources to

preserve habitat and to maintain or restore population levels of particular wildlife species.

In the process of surveying for the needs of

endangered species, the spotted owl (Strix

occidentalis) was identified as a species whose

numbers were declining, possibly to the point of

extirpation (Remsen l978). The major reason for

the decline was a reduction in old-growth and

mature forest, the habitat the owls require. The

purpose of this paper is to report on the status

of the spotted owl in California and to discuss

the ways in which the CDF&G is attempting to

maintain this species and its habitat.

CDF&G; ACTIVITIES

The first activity the CDF&G participated in was

a State-wide survey to determine the distribution

and habitat requirements of spotted owls (Gould

1974). Present activities include: continuously

monitoring populations of spotted owls to determine how constant the occupancy of territories

21
is, what the distribution of territories is 

across the State, and regional trends in populations; working with other government agencies 

to coordinate research on spotted owls, which 

includes the habitat requirements and the effects 

of land management on populations; compiling the 

results of research on owls and serving as a 

central source of information on the owl’s 

status, biology, and management; assisting 

Federal, State, and private land managers in 

developing plans and guidelines that will preserve the habitat of spotted owls (Gould 1983); 

and reviewing plans for selling timber and timber 

harvests to ensure that the needs of spotted owls 

are considered. 

CURRENT STATUS OF SPOTTED OWLS 

‘he Department has classified the spotted owl as 

a “bird species of special concern.” This designation carries no special legal status but only 

designates a species as one whose population has 

declined severely or is otherwise so low that 

extirpation is a real possibility. 

Currently three geographically distinct populations that belong to two described subspecies are 

recognized (Grinnell and Miller 1944). The 

northern spotted owl (S. Q. caurina) occurs from 

Mat-in County north along coastal California to 

the Oregon border and east to northeastern Shasta 

County. The California spotted owl (S. Q. 

gccidentalis) is found the length of the Sierra 

Nevada from southeastern Shasta County to 

northeastern Kern County; a second population 

occurs along California’s south coast from 

Monterey County to San Diego County. The status 

of each population seems equally critical, although the nature of current threats vary. 

Within this distribution there are 1,317 sites 

classified as territories (table 1) where (I) a 

pair has been observed; (2) young have been observed between May and September; or (3) a vocal 

defense of an area has been heard or solicited. 

However, this number doesn’t represent the number 

of currently active sites as some sites have been 

abandoned and others may be yet undiscovered. 

It’s difficult to compare current densities of 

spotted owls with past densities. The lack of 

information on the distribution and density prior 

to 1973 can best be demonstrated by the Statei 

wide estimate, made in 1971,, of 30 pairs. 

Therefore, I can only speculate about historical 

densities. Spotted owls have been reported from 

549 different townships throughout California. 

Only one territory has been recorded for most 

townships. However, 6 to II territories have 

been recorded for 37 townships. Twenty-six of 

these townships are in north coast counties, IO 

are in central Sierra Nevada counties, and only 2 

are in south coast counties. Most of these areas 

are not pristine; I have personal knowledge of 

logging occurring in at least half of these townships, and logging probably has occurred in many 

of the others. 

Table 1-KncxJn distribution of spotted owl 

territories in California, June I, 1984 

Present Nos. for Nos. for California 

County number 

known 

Alpine 

Amador 

owls Nevada coast 

Butte 

Calaveras 1’: 

Colusa 2 

Del Norte 41 

El Dorado 75 

Fresno 23 

Glenn I2 

Humboldt 117 

Kern 

Lake :i 

Lassen 

Los Angeles :: 

Madera 24 

Marin 18 

Mariposa 29 

Mendocino 38 

Modoc 1 

Mono 1 

Monterey 

Napa :: 

Nevada 12 

Orange 

Placer 4: 

Plumas 83 

Riverside 

San 248 

Bernardino 

San Diego 21 

San Luis 8 

Obispo 

Santa 17 

Barbara 

Shasta 36 

Sierra 27 

Siskiyou 250 

Sonoma 

Tehama 558 

Trinity 146 

Tulare 

Tuolumne t; 

Ventura 6 

Yuba 8 

-------L----------LTotals 1317 

:7 

4: 

75 

23 

1;; 

IO 

18 

II 

3 

13 

24 

18 

29 

38 

I 

I 

9 

4 

I2 

z: 

22 14 

27 

250 

4zr 12 

146 

2; 

8 

2 

4 

28 

21 

8 

17 

6 

720 486 III 

One could infer that densities of five territories of spotted owls per township probably were 

not uncommon historically. Using a conservative 

historical density of 3.5, or 32 percent of the 

currently known maximum density, provides an 

estimate of the spotted owl population that existed in pristine times at almost 2,100 territories. This assumes that current distribution and 

historical distribution are the same and that 

historical density was I.6 times current density. 

’ Personal communication, Ned Johnson, University 

of California, Berkeley. 

22 
There is good evidence that historical distribu- logging will reduce owl habitat and spotted owl

tion was more extensive than the current distribution. Spotted owls are no longer present at at

populations; it is doubtful that viable populaleast 30 of approximately 125 historical sites

tions of this species will be maintained unless

(Gould 1974). This implies that the minimum

some accommodations are made. Similar logging is

historical range of spotted owls included at

occurring on BLM and privately owned timber lands

b

least 105 more territories than calculated above.

with few or no restraints to protect spotted

owls.

Population trends can be implied both from trends

T

in the density of owls and from trends in the

numbers of territories over a period of time.

The trend of a reduction of density and range

that was calculated above shows a reduction of at

least 50 percent. Other evidence of a decrease

in spotted owls was gathered in a survey in 1974;

spotted owls were present at only 73 percent of

the previously reported occupied sites (Gould

1974). Because the time between the first

sighting and the most recent sighting varied, it

was impossible to determine the rate of loss.

However, over the last 10 years the Department

has monitored 1,317 territories; at the It's

visit, 58 of these sites were not occupied.

possible that spotted awls were present but not

detected or that the site was of marginal quality

to begin with and isn’t consistently occupied. I

calculate that 1,259 of the 1,317 territories are

presently occupied--a reduction of 4.5 percent

over 10 years. This population size probably is

smaller because those territories with the highest disappearance rate are those where only one

report has been received for that territory and

that report was of a single individual. Of the

1,259 occupied territories, 407 of these are

c single sightings of individual owls; pairs have

been verified at only 41.6 percent of the

territories.

Table 2--Land ownership of spotted owl

territories in California, 1978

Ownership

pattern

Percent territories

bv subspecies Total

Northern California percent

Completely private 4.5 4.0 4.2

1.5 10.9 6.2

40.6 44.6 42.6

31.2 26.2 28.7

5.4 1.0 3.2

2.5 4.5 3.5

3.0 5.9 4.5

2.5 0 1.2

0.5 2.0 1.2

6.4 1.0 3.7

B

As the number of territories increases the chance

of adding new territories decreases. The USDA

Forest Service has intensively surveyed 10 of the

17 National Forests in California; four other

forests have been lightly surveyed. Surveys have

covered from 50 to 85 percent of Forest Service

lands, with most areas about 75 percent surveyed.

Other lands were not as well surveyed; but these

lands probably don’t provide habitat for many

spotted owls.

Private near

Federal land

Completely

Forest Service

Forest Service

with private

land nearby

Bur. of Land Mgmt.

with private

land nearby

Jointly owned by

Federal agencies

Ccmpletely National

Park Service

NPS with private

land nearby

Completley State

park land

State park land

with private

land nearby

Other 2.0 0 1.0

The California Region (Region 5) of the Forest

Service controls 19,680,327 acres of land (USDA

Forest Service 1979), much of it forested. Additional land is controlled by the Bureau of Land

Management, but much less is forested. Large

quantities of privately owned forest land exist

but were the first areas logged; suitable owl

habitat (old-growth and mature forest) is now

scarce. Forests also occur in some State and

Federal parks. On these lands, timber harvest

does not occur and old-growth and mature forest

habitat is usually the management objective.

The preference of spotted owls for old-growth

habitat has been well documented (Forsman 1976,

1980; Forsman and others 1977; Gould 1974; Marcot

1978; Marcot and Gardetto 1980; Solis and

Gutie’rrez 1982).2 Old growth functions as the

thermal cover necessary for the owl’s survival

(Barrows 1980, 1981; Barrows and Barrows 1978).

The general biology and seasonal habitat use of

the northern spotted owl has been described

(Forsman 1976,1980; Solis and Gutiérrez 1982).

Ongoing research is documenting the winter habitat use of the northern spotted owls and the

dispersal of young.3 Also, year-round habitat

use, occupation patterns, and the dispersal of

young are being studied in a central Sierra

Nevada population of the California spotted Owl.4

More spotted owls are found on Forest Service

land than on that in any other ownership (table

2) (Gould 1979); this clearly demonstrates the

importance of Forest Service land to the preservation of this species in California. Currently,

this land is being logged. It has been estimated

that all commercially suitable old-growth forest

habitat will be cut within 25 years. This

2

 Unpublished Progress Report, 1981, “Habitat

use by radio-tagged northern spotted owls on the

Six Rivers National Forest,” by David M. Solis,

Jr., and Chuck Sisco, Six Rivers National Forest,

Eureka, CA.

3

 Personal communication, Chuck Sisco and Ralph

Gutigrrez, Wildlife Department, Humboldt State

University, Arcata, CA.

4

 Personal communication, Stephen Laymon, School

of Natural Resources, University of California,

Berkeley.

23
COORDINATION IN LAND MANAGEMENT

The Department has collaborated with the USDA

Forest Service and the State Board of Forestry in

an effort to manage spotted owls. Both efforts

involved trying to establish land management

plans and regulations.

In 1983, under the California Forest Practices

Act, the Board of Forestry listed species that

must be considered in the planning of timber

sales on private land. This list contains the

species designated as “rare” or “endangered” by

California or designated as a species of special

concern by the Board. The Department made recommendations to the Board for establishing the list

of species and the timber management activities

that should be required to protect these species.

The Department also acted in an advisory capacity

to the Board in their deliberations. The Board

didn’t list the spotted owl as a species of

concern because of a lack of information, and

because of the large territory size and the

amount of potential timber that might be tied up

by any single spotted owl territory.

Collaboration with the Forest Service at the

field level has involved input and comment on

individual timber sale plans by Department biologists. These area biologists review proposed

sales and comment on the effects of the proposed

sale on wildlife resources and suggest mitigation

or alternatives to reduce the impact.

At the staff level, collaboration has involved

the exchange of survey and research data, establishment of guidelines for spotted owl management, and the review of individual forest plans

to determine if these plans comply with the

guidelines. To date, 36 surveys have been performed by individual forests or ranger districts.

These surveys have provided more records of

spotted owls than has any other survey effort.

In 1981, the Department assisted the Pacific

Northwest Region (Region 6, Portland) of the

Forest Service by participating in a workshop

assessing regional spotted owl management guidelines. Similar assistance was given to the Pacific Southwest Region (Region 5, San Francisco).

The Department has a representative on the Forest

Service’s regional review team (Region 51 that

evaluates the land management plan for each

forest. Both Department staff and area biologists review and comment on the wildlife portion

of each forest plan. Spotted owls are a major

concern in the Department’s review of these

plans.

IMPROVEMENTS NEEDED IN COLLABORATIVE EFFORTS

The Department is a single purpose agency and

precise agreement with other agencies and private

groups on land management decisions is not always

possible. This is especially true when dealing

with agencies that are either single purpose or

have a very dominant purpose that is not compatible with the complete maintenance of the wildlife resource.

Because of conflicts in resource use, compromises

Often must be made. With compromises wildlife

always loses something. In the case of the

spotted owl, compromise results in a decrease in

available habitat and in putting the species in

an ever more precarious position. Under such

circumstances it is difficult to achieve the

State’s objectives of maintaining intrinsic and

ecological values, providing use and enjoyment to

the citizens of California, and maintaining aesthetic, educational, and nonappropriative uses.

There must be limits to compromise once the

resource no longer adequately provides these

attributes.

There are several problems concerning spotted

owls that result when land management agency

objectives don’t fully coincide with wildlife

resource objectives:

1. The State Board of Forestry didn’t designate

the spotted owl as a species of concern. As a

result it lacks the protection that it and many

other old-growth forest species need on private

lands. Spotted owls are among the best indicators of old-growth forest quality still found in

the state’s forests.

2. Although the Forest Service considers spotted

owls in their land management planning effort,

the plans, their guidelines and the manner in

which they are being implemented may not offer

adequate protection to maintain viable populations throughout California. More specifically:

3

a. The planning process is biased towards the

timber resource so that the preservation of

other resources is jeopardized regardless of

what alternative is chosen (CHEC 1984).5

b. The plans are supposed to maintain a

viable population of spotted owls but much of

the information needed to determine what constitutes a viable population hasn’t been

gathered.

c. There is no level of viability (probability of species survival) set in the planning

process. Since a viab e population level is

not fixed through time,6 the level of viability set in the management plans must accommodate the worst possible situation; the plans

don’t make this accommodation.

d. An inordinate delay is occurring between

the establishment of guidelines, the development of plans, and the implementation. Because the harvest of old-growth forests is

5

 Correspondence, H. E. Hodgdon, The Wildlife

Society, letter of 4/9/84 to T. E. Hamilton,

Director, RPA, U.S.D.A. Forest Service, Bethesda,

MD, 5 p.

6 Unpublished Administration Report, 1983,

"Wildlife population viability--a question Of

risk,” by Hal Salwasser and Stephen P. Mealey, 9

USDA Forest Service, Pacific Southwest Region,

San Francisco, CA.

24
continuing, it is likely that the plans will

not be able to be implemented as written and

Planning guidelines will not be met.

3. The Bureau of Land Management, National Park

Service, California State Board of Forestry,

California Department of Parks and Recreation,

and California Department of Forestry do not have

any State-wide, long-term planning efforts that

consider spotted owls.

The Department also needs to develop a plan for

preserving old-growth and mature forest ecosystems. It has already done this type of planning

for coastal wetlands. A plan for old growth

forests should include an inventory of the remaining old growth, a list of species that must

be accommodated in forest preservation, a description of the current and the desired status

of the forest wildlife in California, and procedures for working with land management agencies

to carry out the plan. To be effective, the plan

must be implemented promptly because all the

commercially available old-growth forest may be

harvested within 25 years, and the sales for

those harvests are likely to be planned within

the next 10 years.

INFORMATION NEEDS

It’s obvious that the multiple use of forests

can't stop for spotted owls. But, the Department

must demand, and other land management agencies

P must provide for, the preservation of all species

throughout their ranges at ecologically sound

population levels.

+=J3 A species can% be preserved throughout its range

without adequate surveys to delimit the range and

to show patterns of abundance within the range.

Surveys of habitat facilitate the population

surveys, provide information on the potential

range of the species, and the future potential

area available for the species. Survey work

isn’t complete in the species’ believed range in

California. However, in many areas, particularly

in a few National Forests, it is nearly complete.

The most important information that’s needed

concerns the population dynamics of spotted owls.

Data is needed to prepare a life table for a

viable population of owls; specifically needed

are age-specific reproductive rates, age at first

breeding, mortality causes, and age-specific

mortality rates. This information could be used

to model the normal functioning of spotted owl

populations and to predict the population’s ability to reproduce itself and sustain the population. What is required to sustain the population

could be compared to what occurs under different

regimes of habitat disturbance and distribution

4 patterns. The future course of any subpopulation

could be estimated and changes in population size

and distribution could be predicted. Only then

can land management plans be made that would A5 provide a solid basis for maintaining viable

populations.

Finally, the pattern of site occupancy must be

studied to understand and determine the causes

and rates of local extinctions and recolonizations. An extensive monitoring system would have

to be established throughout the species’ range

to collect this information.

REFERENCES

Barrows, Cameron Wallace. Summer roost selection

by spotted owls: an adaptation to heat

stress. Long Beach, CA: California State University; 1980. 51 p. M.S. dissertation.

Barrows, Cameron W. Roost selection by spotted

owls: An adaptation to heat stress. Condor.

83: 302-309; 1981.

Barrows, Cameron; Barrows, Katherine. Roost

characteristics and behavioral thermoregulation

in the spotted owl. Western Birds. 9: l-8;

1978.

CHEC. Review of the 1985 RPA Program. Eugene,

OR: Cascade Holistic Economic Consultants;

1984. 31 p.

Forsman, Eric. A preliminary investigation of

the spotted owl in Oregon. Corvallis, OR:

Oregon State University; 1976. 127 p. M.S.

dissertation.

Forsman, Eric D. Habitat utilization by spotted

owls in the west-central Cascades of Oregon.

Corvallis, OR: Oregon State University; 1980.

95 p. Ph.D. dissertation.

Forsman, Eric D.; Meslow, E. Charles; Strub,

Monica J. Spotted owl abundance in young versus old-growth forest, Oregon. Wildlife Society

Bulletin. 5(2): 43-47; 1977.

Gould, Gordon I., Jr.; The status of the spotted

owl in California. Sacramento, CA: California

Department of Fish and Game, Wildlife Management Branch; 1974; Admin. Rep. 74-6. 56 p.

Gould, Gordon I., Jr.; Status and management of

elf and spotted owls in California. In:

Schaeffer, P.; Ehlers, S., eds. Owls of the

West; 1979 January 20; San Frncisco, CA.

Tiburon, CA: National Audubon Society, Western

Education Center; 1979:86-97.

Gould, Gordon I., Jr.; Owl nest territory monitoring program. Sacramento, CA; California

Department of Fish and Game, Nongame Wildlife

Investigations; 1983; Progress Rep. Project W54-R-15, Job II-3. 6 p.

Grinnell, Joseph; Miller, Alden H. The distribution of the birds of California. Pacific Coast

Avifauna. 27: 203-205; 1944.

Marcot, Bruce G. Prolegomena of the spotted owl

(Strix occidentalis) in Six Rivers National

Forest. Eureka, CA: Six Rivers National

Forest; 1978; Tech. Rep. 48 p.

25
Marcot, Bruce G; Gardetto, Jeffrey. Status of

the spotted owl in Six Rivers National Forest,

\ California. Western Birds. 11: 79-87; 1980.

Remsen, J.V., Jr. Bird species of special concern in California. Sacramento, CA: California

Department of Fish and Game, Wildlife Management Branch; 1978; Admin. Rep. 78-l. 54 P.

Solis, David M., Jr; Gutirrez, Ralph J. Spotted

owl habitat use on the Six Rivers National

Forest, Humboldt County, California. Eureka,

CA: Six Rivers National Forest; 1982; Final

Rep. 230 p.

USDA Forest Service. Land Areas of the National

Forest System as of September 30, 1979. Washington, DC: Department of Agriculture, Forest

Service; 1979.

26
STATUS OF SPOTTED OWL MANAGEMENT IN OREGON AS PERCEIVED

BY OREGON DEPARTMENT OF FISH AND WILDLIFE

Richard D. Carleson and William I. Haight

ABSTRACT: The Oregon Department of Fish and Wildlife has a legal mandate to

prevent serious depletion of wildlife species indigenous to Oregon. Because

the population of spotted-owls appeared to be threatened by timber

harvesting, the Department took the lead in organizing an interagency

wildlife committee. The committee, composed of representatives of land and

wildlife management agencies, developed a Spotted Owl Management Plan. The

plan calls for maintaining a minimum of 400 pairs of spotted owls in Oregon;

the present population is l,OOO-1,200 pairs. But cooperation and

coordination among the land management agencies must be increased to

accomplish this plan. And many questions, such as what constitutes a viable

population, need to be answered.

INTRODUCTION SPOTTED OWLS ON BLM AND PRIVATE LAND

We estimate the present population of spotted

owls (Strix occidentalis) in Oregon to be

l,000-1,200 pairs based on recent research by

Forsman and others (1984). The Spotted Owl

Management Plan recommended by the OregonWashington Interagency Wildlife Committee calls

for maintaining 400 pairs in Oregon. Comparing

the two numbers, it appears that the present

population is high enough to maintain a viable

population of spotted owls throughout most of

=A, their range in Oregon if sufficient habitat can

be retained.

A

rl

RICHARD D. CARLESON and WILLIAM I. HAIGHT are

wildlife biologists, Oregon Department of Fish

and Wildlife, Portland, Oreg.

Although the present statewide population is

around l,000-1,200 pairs, there probably is not

sufficient habitat to support that number, even

in the short term. Timber harvest patterns have

incrementally nibbled away at what were once vast

acreages of old growth, creating a high

interspersion of clearcutting with old growth in

some ownerships, particularly the checkerboards

of private and Bureau of Land Management (BLM)

lands in western Oregon. There the remaining

old growth is highly fragmented with few

l,OOO-acre blocks of good spotted owl habitat.

The gross acreage of old growth remaining in

western Oregon is high enough to give the

mistaken impression that there is plenty of

habitat available. The fragmented habitat

appears to allow existing spotted owls to survive

in the short term, it is unclear whether they

will be able to reproduce well enough to persist

27
indefinitely. For example, 16 Spotted Owl

Management Areas (SOMA) on the Coos Bay BLM

District were surveyed in 1984 and only eight

were occupied by spotted owls. Only one pair

produced offspring. Spotted owl habitat on

private land is, for the most part, already gone.

Most of the old-growth stands large enough to

contribute to a comprehensive spotted owl management plan were already harvested or committed to

timber harvest before the Spotted Owl Management

Plan was written.

The BLM lands in western Oregon offer better

promise of maintaining spotted owl habitat than

on private lands. Although sections of BLM land

alternate with sections of private lands, BLM land

still contains spotted owls and old-growth forest.

Four out of five western Oregon BLM districts

(Coos Bay, Salem, Eugene and Roseburg) completed

ten-year timber management plans in 1983.

Inventory data presented in the BLM impact statements showed the existing population of spotted

owls to be 177 pairs: the timber management plans

protect the habitat of 64 pairs for 10 years. The

protective standards, however, maintain only 300

acres of old-growth forest per spotted owl pair.

According to the environmental statement, only 17

of the 64 SOMAs meet the minimum standards of the

Spotted Owl Management Plan (SOMP) recommended by

the Oregon-Washington Interagency Wildlife

Committee. Because the BLM plans were regarded

by the Department to need better protection of

spotted owls, the department and BLM signed a

cooperative agreement to provide needed protection

for at least the first five years of the plans.

The cooperative agreement is described later in

this paper.

SPOTTED OWLS ON FOREST SERVICE LANDS

The spotted owls on the National Forests have

more potential for survival. The forests haven't

been as extensively harvested as BLM lands, so

bigger blocks of old-growth habitat remain. A

desirable distribution of SOMAs may be difficult

to obtain, because the Forest Service ownership

is not continuous from border to border (north

and south) in the Coast Range. The planning

process for the Forest Service is only partly

completed, but there seems to be acceptance of

the need to protect the habitat for owl pairs in

close compliance with Oregon's Spotted Owl Management Plan. The Forest Service was allocated 290

pairs out of the 400 pairs recommended as minimum

to maintain a viable population in Oregon

throughout their range.

ODFW And The Spotted Owl

The overriding statement directing the Oregon

Department of Fish and Wildlife (ODFW) is in the

Wildlife Policy (Oregon Revised Statutes 496.012)

adopted by the Oregon legislature in 1973. The

appropriate part of the law is as follows: "It

is the policy of the State of Oregon that Wildlife

shall be managed to provide the optimum

recreational and aesthetic benefits for present

and future generations. of the citizens of this

state...maintain all species of wildlife at

optimum levels and prevent the serious depletion

of any indigenous species...". The law does not

define what the "optimim levels" are, nor does it

establish what constitutes "serious depletion".

The statutes authorize the Governor to appoint a .*

seven member Commission to develop and implement -

policies and programs of the State for the management of wildlife and to promulgate rules to carry

but the provisions of the wildlife laws. The

wildlife laws relate mostly to the management and T

use of wildlife species. Traditionally, management of the land and its value as habitat has been

at the discretion of the landowner. The end

result is that the Commission can, by rule,

regulate the taking or molestation of a species,

but has only limited authority to regulate habitat

management on the lands of others. The department

does seek habitat protection through laws and

regulatory mechanisms of other agencies such as

Oregon Forest Practices Act and National Forest

Management Act. The Commission did pass an

administrative rule prohibiting the taking of

sensitive wildlife, including State-listed

threatened and endangered wildlife, and all

nongame birds except sparrows and starlings. The

ODFW was given authority to manage nongame

wildlife by the 1971 legislature. Prior to that

time authority was limited to game mammals and

gamefish. A chronology of ODFW actions concerning

the spotted owl follows:

May 1973.--John W. McKean, Director, Oregon Game

Commission, proposed that a professional task

force be formed and that its initial emphasis be J

placed on the identification of habitat requirements for the northern spotted owl (S.

occidentalis caurian).

The Oregon Endangered Species Task Force was 'I

established and recommended the adoption of

statewide guidelines by June 30, 1974. Protection

of 300 acres around each known northern spotted

owl location was recommended as an interim

protective measure pending the completion of a

management plan. At that time there was no

information on the extent of acres used for forage

by spotted owls. For this reason, the 300-acre

guideline was adopted only as an interim measure,

to be altered, if necessary when additional data

became available.

October 1974. --The Sikes Act, Public Law 93-452,

became law and provided for the protection for

fish and wildlife, "officially classified as

threatened or endangered pursuant to Section Four

of the Endangered Species Act of 1973 or

considered to be threatened, rare, or endangered

by the State agency."

January 1975.--The Oregon Wildlife Commission

adopted a list of threatened and endangered

wildlife in Oregon. The northern spotted owl was *

listed as a threatened species on the official

State list. Federal land managers were expected

to provide protection for those species under the

Sikes Act. s

In 1977 the Oregon Endangered Species Task Force

was reorganized into the Oregon-Washington Interagency Wildlife Committee, a multiagency group

28
formed to coordinate the activities of wildlife

and land management agencies. It appointed a

Spotted Owl Subcommittee. At this time ODFW's

previous role as being solely responsible for

.k. formulating a spotted owl management plan became

a shared responsibility with the other agencies.

The Spotted Owl Subcommittee completed a Spotted

.F Owl Management Plan in late 1977. Through the

Wildlife Committee the plan was transmitted to

concerned agency administrators for review and

comment. The objective of the plan was “to

maintain a population of at least 400 breeding

pairs of northern spotted owls distributed

throughout the known range in Oregon". The

Bureau of Land Management accepted responsibility

for the protection of 90 pairs; the USDA Forest

Service, 290 pairs; and combined, state lands

(Department of Forestry, Oregon Department of

Fish and Wildlife, and Parks Division), county

lands, Crater Lake National Park and private

lands were to protect 20 pairs. Eash SOMA was to

be at least 1,200 acres in size and to include at

least 300 acres of old-growth forest. The Forest

Service and BLM both agreed to implement the SOMP

on an interim basis.

In 1981, after telemetry research on spotted owls

indicated that the SOMP might not protect enough

old-growth habitat, the subcommittee revised the

SOMP to increase the old growth in each SOMA to

1,000 acres.

G March 1981. --In March 1981, the Oregon-Washington

Interagency Wildlife 'Committee adopted the

Spotted Owl Subcommittee's revision to the Oregon

SOMP. Robert M. Stein, chairman of the

4

committee, forwarded the revised SOMP to the

Regional Forester, Pacific Northwest Region, USDA

Forest Service; State Director, BLM; and the

Oregon State Forester for use in forest land

planning. Formal acknowledgement of the

acceptability of these revisions was not

forthcoming from the Bureau of Land Management or

the Oregon Department of Forestry. The Forest

Service agreed to incorporate the revised

standard into its planning activities.

September 1982. --When the first of five BLM

timber management plans was proposed in September

1982, the Oregon Fish and Wildlife Commission

found the proposal to be in violation of Oregon's

Wildlife Policy, the Federal Sikes Act, and the

Oregon Coastal Management Plan. One of the

deficiencies in the plan was that only 300 acres

of old growth per SOMA were to be protected

instead of the 1,000 acres called for in the

Spotted Owl Management Plan.

October 1983.--In the summer of 1983 all five BLM

Timber Management Plans were adopted by the

A Bureau with the additional deficiency that the

number of spotted owl pairs to be protected was

less than called for in the SOMP.

5

After a series of negotiations involving several

agencies and media exposure, an agreement was

reached between the ODFW and BLM. The BLM agreed

to manage spotted owl habitat in accordance with

the best available scientific information for a

period of 5 years and ODFW would not pursue a

legal challenge to the timber management plans.

The agreement will provide sufficient habitat

protection in the interim, but long-term

protection requires successful completion of

present research and reevaluation of the SOMP and

timber management plans at the end of the five

year period. ODFW and the BLM are presently

evaluating implementation of the agreement.

'The distributional requirements of the spotted

owls are as important as habitat quality and

quantity, and we are in the process of

coordinating the disribution of SOMAs between the

USFS and BLM.

There are no ongoing discussions with private

landowners about maintaining spotted owl

habitat. Most private holdings have been

harvested, are too small to make a habitat unit,

or have not been inventoried for spotted owls.

Further, the bulk of the SOMAs (380 out of 400)

have been allocated to the most extensive land

managers (BLM and Forest Service); it seems

reasonable to first secure protection on those

lands, and then try to fit the remaining 20 SOMAs

into the distribution provided by federal lands.

State lands do hold some spotted owl habitat, but

population inventories have not been made. State

lands are managed by various State agencies each

having differing legal mandates. The majority of

State lands are managed for timber production by

the Oregon Department of Forestry.

Needed Collaboration

Development of the Spotted Owl Management Plan

provided a necessary tool for protection of

spotted owl habitat. It was intended to give

land managers a recipe for protection that, if

implemented, would maintain a minimum viable

spotted owl-population throughout its native

range in Oregon. The SOMP represents minimum

standards and the responsibility for success of

the plan depends on implementation of the plan by

each of the major landowners. There needs to be

more coordination among the agencies responsible

for implementing the plan. The coordination is

difficult because the agencies have differing

schedules for completing their land use plans.

The plans of one land manager will affect the

outcome of the plans of another agency. To make

certain that spotted owl habitat units are

distributed properly there must be continuous

discussion among the agencies. Since the Spotted

Owl Subcommittee has become more active, the

interagency coordination has improved. It is

expected that continued coordination by members

of the Spotted Owl Subcommittee will provide

updated direction to the land management agencies

The Spotted Owl Management Plan is dynamic and

needs to reflect new research findings. The

Subcommittee is expected to continuously evaluate

the SOMP to see that it is state-of-the-art and

to monitor its implementation by land managers.

29
INFORMATION NEEDS

Many papers end with the statement that more

research is needed; this paper is no exception.

More answers are needed and are needed soon to

such questions as: What is needed to ensure the

continued existence of spotted owls? Is the

population in Oregon isolated from the one in

Washington? If so, is there a potential link

somewhere in the Columbia Gorge? Can old-growth

habitat be successfully managed to provide timber

and old-growth-dependent wildlife? Can spotted

owl habitat be created? How much fragmentation

of old-growth habitat can be tolerated within a

SOMA? Does a fragmented SOMA need more acreage

of old growth than an unfragmented SOMA, and if

so, how much? Some of the SOMAs being selected

by land managers appear to be in marginal

habitat; can the parameters of the SOMP be

successfully applied to marginal habitat? The

questions could go on and on. Unfortunately it's

easier to find the questions than it is to find

the money to fund the answers. -3

LITERATURE CITED

PC

Forsman, Eric D.; Meslow, E. Charles; Wight,

Howard M. Distribution and biology of the

spotted owl in Oregon. Wildlife Monograph No.

07; 1984. 64 p.

30
MANAGING NORTHERN SPOTTED OWLS IN WASHINGTON:

THE POSITION OF THE WASHINGTON DEPARTMENT OF GAME

Tom Juelson

ABSTRACT : The northern spotted owl is classified as threatened by the

Washington Department of Game. The Department considers the Olympic

Peninsula spotted owl population to be isolated from all others and

considers the Washington Cascade Range population to be genetically isolated

from Oregon spotted owls by the Columbia River. The principal

responsibilities of the Department are to protect and improve wildlife

habitat, and to preserve, protect, and perpetuate wild animals in the best

interest of the people of Washington. The responsibility of the Department

to spotted owls is implicit under these guidelines. The Department is

involved in independent research as well as interagency cooperative research

regarding the spotted owl. Further collaboration among agencies is needed,

particularly in managing the Olympic Peninsula spotted owl population.

There are additional research needs in reference to the spotted owl which

should be addressed.

STATUS OF THB SPOTTED OWL

The Washington Department of Game has classified

the northern spotted owl as a threatened species

in Washington. The State's definition of

"threatened" is the same as that of the U.S. Fish

and Wildlife Service. This spotted owl classification is currently under review for a possible

change to "endangered". The final decision on the

status is pending completion of research in

Washington.

TOM JURLSON is the nongame program manager,

Washington Department of Game, Olympia, Washington.

Department biologists currently perceive the

spotted owl population in Washington as divided

into two gene pools. One exists on the Olympic

Peninsula. These spotted owls are isolated from

genetic interaction with others because of large

expanses of water and nonforested areas. The

habitat there is severely fragmented for the most

part and in short supply. It may be too late to

provide enough habitat on the Peninsula to

support a viable population, and it is highly

unlikely that a forested corridor will be

established linking the Peninsula with the

Cascade Range in Washington. Some biologists

consider the long-term existence of this segment

of the spotted owl population to be endangered by

any criteria.

31
The second spotted owl gene pool in Washington is

in the Cascade Range. This range includes the

wet-type forests of western Washington and the

dry-type coniferous forests of the eastern slopes

of the Cascades.

The Department believes the Washington Cascades

spotted owl population may be genetically

separated from the Oregon population by the

Columbia River and by adjacent land use in the

river valley. The Washington Cascades population

is continuous with the British Columbia spotted

owl population; however, current information

indicates that the British Columbia segment of

the population is probably very small.&/

Management considerations for the Washington

Cascades spotted owl population, along with

members of that population in British Columbia,

should be based on a viable population level

separately derived for the geographic area north

and west of the Columbia River. Department

biologists do not believe a satisfactory viable

population level has been determined.

DEPARTMENT OF GAME POLICY

The policy manual of the Washingtn Department of

Game provides a "statement of purpose" for each

administrative division within the agency. Two

of these divisions share the principal

responsibilities with regard to the northern

spotted owl: the Habitat Management Division and

the Wildlife Management Division. The goal of

the Habitat Management Division is "to protect

and improve land and water habitats to assure

optimal numbers, diversity, and distribution of

wildlife for the welfare of people of Washington

State." The goal of the Wildlife Management

Division is "to preserve, protect, and perpetuate

wild animals and to provide optimum wildlife

oriented recreation for citizens of Washington

through management, surveys, and research of

birds, mammals, reptiles, and amphibians and

their habitat." The spotted owl is a native

species of Washinton and the responsibility of

the Department toward management of this species

is implicit in these two statements.

COLLABORATIVE EFFORTS

The Department initiated independent research on

spotted owl ecology in 1981 (Allen and Brewer

1985) which has stimulated a number of

cooperative efforts between state and federal

agencies and interactions between state and

private industry in Washington. The Department

is cooperating with three National Forests in

Washington in an administrative study of the

effectiveness of spotted owl management areas

(Carey and Ruggiero 1985). USDA Forest Service,

Burlington Northern Railroad, Weyerhaeuser

Company, and USDI National Park Service personnel

cooperated with the Department in completing a

statewide spotted owl survey. Department

biologists are interacting with USDA Forest

Service district biologists on many aspects of

spotted owl information sharing (for example, &

location information, home range data, and

habitat data). Department personnel are

negotiating with the Washington Department of

Natural Resources regarding Natural Resources

policy on spotted owl management. Department

3

research biologists are cooperating with wildlife

management biologists from British Columbia in

setting up spotted owl censuses in British

Columbia that are targeted for spring 1985. The

Department is conducting radio-telemetry

monitoring of spotted owls on two ranger

districts for the USDA Forest Service. This work

is funded by timber sale revenues

(Knutson-Vandenberg Act funds).

ADDITIONAL COLLABORATION NEEDED

A generally acceptable determination of a viable

population level for spotted owls in the

Washington Cascade Range and in the British

Columbia populations should be made through an

interagency approach. The U.S. Fish and Wildlife

Service should consider reviewing the spotted owl

population on the Olympic Peninsula to see if it

should be declared endangered. If it is,

cooperative efforts should be initiated to

develop and carry out a maintenance program of

the current population level. The Oregon- 24:

Washington Interagency Wildlife Committee and its

Spotted Owl Subcommittee are developing means for

interagency collaboration.

INFORMATIONAL NEEDS

To complete the evaluation of the size and

distribution of the Washington and British

Columbia spotted owl populations, we need good

data on the British Columbia population. Genetic

research to determine the extent of inbreeding in

current populations would further facilitate the

evaluation of species status.

The effects of habitat fragmentation and the size

and distribution of habitat blocks on population

should be more clearly defined, particularly with

regard to predation and interspecific competition.

An analysis of habitat use in dry-type coniferous

forests is needed to define the limits of spotted

owl range in eastern Washington. This is

particularly important in deciding the location

of Spotted Owl Management Areas in dry-type

forests.

Additional information on the relationship E

bewteen prey species and spotted owl habitat use

is needed to assess the merits of alternative

forest practices (that is, selective harvest).

s

5

1/ Personal communication, D. Dunbar and D.

Wilson, B.C. Fish and Wildlife Management,

Parliament Bldg., Victoria V8V 1X5.

32
LITERATURE CITED

Allen, Harriet; Brewer, Larry W. A review of

current northern spotted owl (Strix

&

occidentalis caurina) research in Washington

State. In: Gutiérrez, Ralph J.; Carey, Andrew

B, tech eds. Ecology and management of the

spotted owl in the Pacific Northwest. Gen.

Tech. Rep. PNW-185. Portland, OR: U.S.

.T Department of Agriculture, Forest Service,

Pacific Northwest Forest and Range Experiment

Station; 1985: 55-57.

Carey, Andrew B.; Ruggiero, Leonard F. Spotted

owl management: meeting NFMA requirements

through monitoring. In: Gutiérrez, Ralph J.;

Carey, Andrew B., tech. eds. Ecology and

management of the spotted owl in the Pacific

Northwest. Gen. Tech. Rep. PNW-185. Portland,

OR: U.S. Department of Agriculture, Forest

Service; Pacific Northwest Forest and Range

Experiment Station; 1985: 34-38.

33
.

SPOTTED OWLMANAGEMENT: MEETING NFMA REQUIREMENTS THROUGH MONITORING

Andrew B. Carey and Leonard F. Ruggiero

ABSTRACT: In 1983, biologists from USDA Forest Service research, three

National Forests in Washington, and the Washington Department of Game

collaborated to design and implement an extensive program for monitoring

the effectiveness of the management area system for spotted owls-a

designated management indicator species and key vulnerable species. The

program will evaluate the success of the management system as well as

current standards and guidelines for management. This kind of

collaborative effort may be the only practical way to effectively monitor

a species that is possibly in jeopardy from the reduction of its habitat.

INTRODUCTION

The USDA Forest Service is charged with the

authority and responsibility for managing the

National Forests. Accompanying papers

(Beckstead 1985, Carrier 1985, Lee 1985,

Ruediger 1985) relate the procedures used and

the difficulties encountered in planning for and

making decisions about northern spotted owls

(Strix occidentalis caurina). What, then, are

the risks of making such decisions with

incomplete information? For the spotted owl,

wrong decisions or unexpected results could

place in jeopardy the subspecies' existence,

lead to a change in its legal status (for

ANDREW B. CAREY is research coordinator and

LEONARD F. RUGGIERO is program manager,

Old-Growth Forest Wildlife Habitat Program,

Pacific Northwest Forest and Range Experiment

Station, USDA Forest Service, Olympia, WA.

example, it could be placed on the Federal

Endangered Species List), and incur stringent

constraints on future forest management. Worse,

the subspecies could be extirpated from much of

its range. Both situations would be failures in

meeting management objectives as well as legal

requirements.

What can be done to reduce the risks associated

with making decisions based on incomplete

information? Conservative decisions-those that

assume the worst case-can be made. Advice can

be obtained from persons most knowledgeable

about the species. Research can continue to

produce new information. Most importantly, &

however, the effects of the decisions can be

monitored to determine if the objectives and

expected results are being attained. The

purpose of this paper is to discuss monitoring 5

and to describe a monitoring program recently

implemented in the National Forests in

Washington to determine how well the Spotted Owl

Management Area (SOMA) system is working.

34
MONITORING

Monitoring is an integral part of modem management systems. It provides information on the

quality and quantity of the products of management and on the degree of attainment of goals

and objectives. Monitoring provides an

evaluation of the reasonableness of objectives

and the efficacy and suitability of the processes

(management actions) used to achieve the

objectives. And monitoring provides information

for future management.

The USDA Forest Service has adopted a goaloriented approach to its management of wildlife

and fish (Nelson and others 1983). Now the

National Forest System is developing monitoring

systems that are in accordance with legal

requirements and management needs. Carey (1983)

and Verner (1983) provide examples of how

monitoring systems might be developed and advice

on experimental design and sampling considerations for monitoring. Legislative mandates for

monitoring the attainment of goals and objectives

of wildlife and fish management were reviewed by

Salwasser and others (1983). The National

Environmental Policy Act of 1969 (NEPA), the

subsequent regulations formulated by the Council

on Environmental Quality, and, later, Executive

Orders provide the basis for most of the requirements for monitoring by Federal agencies.

The regulations stemming from the National Forest

Management-Act (MacCleery 1982) provide the most

explicit direction for monitoring by the National

Forest System. The regulations require that

monitoring be "addressed" in both the regional

guide and forest plan. "On a sample basis",

monitoring is to periodically determine and

evaluate the effects of management practices,

how closely management standards and guidelines

have been applied, and how well objectives have

been met. An important "minimum specific management requirement" is to provide for adequate

habitat to maintain viable populations of

existing native vertebrate species and to ensure

that habitat for management indicator species is

maintained or improved to the degree consistent

with the multiple-use objectives established in

the forest plan. The population trends of

management indicator species must be monitored

and relationships to habitat changes determined.

Monitoring of populations is to be done in

cooperation with State fish and wildlife

agencies, to the extent practicable.

The Pacific Northwest Region (R-b-the National

Forests in Oregon and Washington) of the National

Forest System lists the northern spotted owl as

a management indicator species and as a "key

vulnerable species"--a species possibly in

jeopardy because of reductions in its limiting

habitat. 1/ Thus, minimum management require1/ Jeff M. Sirmon. 1983. Regional guidelines

for incorporating minimum management requirements

in forest planning. Written directive to Forest

Supervisors, Region 6, National Forest System,

on file at Pacific Northwest Region, P.O. Box

3623, Portland, OR.

ments (including monitoring) for management

indicator species and for minimum viable

populations apply to the spotted owl.

SPOTTED OWL MANAGEMENT IN R-6

Detailed information on spotted owls in the

Pacific Northwest was first collected in the

1970's. The owl's association with old-growth

Douglas-fir forests was documented and declines

in populations were noted. In 1973 an interagency committee of biologists from the USDA

Forest Service, USDI Bureau of Land Management,

USDI Fish and Wildlife Service, Oregon State

University, and the Oregon Department of Fish

and Wildlife drafted a management plan for

spotted owls. Later, biologists from the

Washington Department of Game (WDG) joined the

committee. R-6 accepted the recommendations of

the committee and subsequent revisions (Forsman

and others 1982).

In 1983, R-6 minimum management requirements

(see footnote 1) for each pair of spotted owls

in a Spotted Owl Management Area (SOMA) were

1,000 acres of old-growth forest with 300

contiguous acres constituting a nest grove (core

area) and 700 acres within 1.5 miles of the

nest, in patches greater than 30 acres,

constituting a foraging area. If 1,000 acres of

old-growth were not available, the next oldest

stands were to be substituted for the old growth.

Each SOMA was to encompass the home ranges of at

least three pairs of owls. Single-pair SOMAs

were acceptable only to improve the geographic

distribution of SOMAs or where remnant habitat

existed. SOMAs of three or more pairs were to

be less than 12 miles apart; the core areas of

multipair SOMAs were to be separated by l-3

miles. Single-pair SOMAs were to be less than 6

miles from other SOMAs (core center to core

center). The National Forests, with the Bureau

of Land Management, were to maintain SOMAs for

400 pairs of owls west of the Cascade Range

crest in Oregon; the National Forests in

Washington (west of the Cascade Range crest)

were to provide sufficient SOMAs to maintain 108

pairs of owls.

Proposed SOMAs were located using owl

distribution maps and habitat descriptions, and

through coordination with other land uses. The

distribution of spotted owls in the National

Forests was determined by eliciting vocal

responses from spotted owls by broadcasting tape

recordings of owl calls at night from roads and

trails in mature and old-growth forest (see

Forsman 1983 for procedures). A SOMA was

considered verified (established) when occupancy

was determined by repeated nocturnal surveys or

when immature owls were observed. In April 1984

the minimum management requirements for the

spotted owl were expanded to reflect the most

recent information on the biology of spotted

owls (see the paper by Lee in this symposium).

The procedures used to choose and verify SOMAs

had several weaknesses, especially when they

were applied in the National Forests in

Washington. First, most research on the spotted

35
owl's habitat requirements had been done in

Oregon and was not specific to Washington.

Second, nocturnal surveys do not precisely

determine an owl's home range and may be

misleading because owls often move towards the

caller before responding. And third, few

nestling or fledgling owls were seen by National

Forest System biologists. For these three

reasons, an extensive monitoring program for

spotted owls in National Forests in western

Washington was developed jointly in 1983 by

Forest Service and WDG biologists. Andrew Carey

and Len Ruggiero represented Forest Service

research; Bill Ruediger, the Gifford Pinchot

National Forest (NF); Dick Dearsley, the Mount

Baker-Snoqualmie NF; Maureen Beckstead and Kelly

Coon, the Olympic NF; and Harriet Allen and

Larry Brewer, the WDG. Earlier, Eric Forsman

(Oregon State University) and Rocky Gutiérrez

(Humboldt State University) had provided the

group with unpublished reports and technical

advice. Funds to implement the monitoring in

1984 were provided by R-6 and the WDG. WDG

personnel are conducting the monitoring with

assistance from the personnel at the National

Forests and under the guidance of the ad hoc

committee of biologists listed above. Total

costs for a 3-year program are estimated to be

$380,000.

MONITORING SOMAS IN WASHINGTON

Objectives

The ad hoc committee formulated 2 primary

objectives and 14 secondary objectives for the

monitoring.

Objective I: Determine if the SOMA system is

working.--It is presently assumed by R-6 that

each SOMA will provide the necessary habitat to

maintain at least one pair of spotted owls. At

least the following will be determined:

1. The proportion of SOMAs occupied by spotted

owls.

2. The proportion of SOMAs occupied by one or

more pairs (male and female) of spotted

owls.

3. The proportion of SOMAs occupied by breeding

pairs of spotted owls.

4. The average number of spotted owls (and owl

pairs) per SOMA.

Objective II: Determine if current standards

and guidelines are appropriate.--At a minimum,

two aspects of current standards will be

evaluated: size of SOMAs and characteristics of

SOMAS. For evaluating size standards, the

following will be determined:

5. The proportion of the SOMA being used by

spotted owls.

6. The amount of areas adjacent to the SOMA

being used by owls.

7. The home range of owls using SOMAs.

8. The home range of pairs of owls using SOMAs.

.

For evaluating characteristics, the following

will be determined:

9. The age of stands used by owls in the SOMAs.

10. The proportion of time spent in old growth

by the owls.

11. The proportion of time spent in young d

forests by the owls.

12. The habitat characteristics (canopy layers,

diameter at breast height, abundance of

snags, and others) of areas used by owls. r$

13. The habitat characteristics of areas not

used by owls, but in or adjacent to the

SOMAS.

14. The differences between used and unused

areas.

Study Areas

Population objectives were 49 pairs of spotted

owls for the Mount Baker-Snoqualmie NF, 42 pairs

for the Gifford-Pinchot NF, and 17 pairs for the

Olympic NF. Each Forest biologist provided us

with a sequentially numbered list of SOMAs equal

in number to that Forest's population objective.

We used a random numbers table to select the

SOMAs to be evaluated: 19 SOMAs were chosen for

the Mount Baker-Snoqualmie NF, 17 for the

Gifford-Pinchot NF, and 10 for the Olympic NF.

A list of alternate SOMAs was also selected for

each Forest in the event one or more SOMAs had

to be eliminated from the sample.

Methods

3

Determination of occupancy.--Forest Service

personnel have surveyed most of the SOMAs for

spotted owls. Thus, for some SOMAs, the primary

center of activity or core area is known.

Because owls range widely and may travel far to

respond to calls at night, the core areas and

actual occupants of many other SOMAs are not

well documented. WDG monitoring crews will

determine occupancy each year for at least 3

years. When the core area is known, the crews

will visit the SOMA during the day to locate the

resident owls. Nocturnal surveys will be made

throughout the other SOMAs. If no owls are

found it will be assumed that the SOMA is

unoccupied that year. If owls are observed,

then the center of activity will be located and

visited during the day. All surveys will be

done from March to August. Up to seven daytime

visits will be made to each SOMA. If owls can't

be found on seven visits, the SOMA will be

classified as unoccupied for that year. If owls

-7‘t

are found, the number, age, and sex of the owls

and their roosting and nesting trees will be

noted. If only one owl is observed at a time,

it will be assumed that the SOMA was not

occupied by a pair. If a pair of owls is seen ,&

or if young owls are seen, it will be assumed

that the SOMA was occupied by a pair of owls.

Occupancy will be determined in each of 3 years.

Use and home range.--Ten occupied SOMAs were

selected for evaluation. Resident owls were

trapped in early spring (1984) and fitted with

radio transmitters. Each owl is being monitored

36
b

A

3

.t

F

m

through radiotelemetry at least 1 day per week

and l-3 nights per week throughout the year.

Areas used for foraging, roosting, and nesting

are being determined. Movements and use

(activity) will be plotted on aerial photographs

or orthophoto quadrangle maps. Altogether, the

proportion of SOMA used, habitats used, and home

range will be determined by season for l0-20

spotted owls.

Description of habitat.--A standard sampling

procedure developed by the Old-Growth Forest

Wildlife Habitat Program for analyzing wildlife

habitat will be used to describe used and unused

areas in, and adjacent to, the SOMAs, with use

determined by radiotelemetry. Both vegetation

and environmental structure will be described.

Results

SOMA effectiveness will be measured by the

following statistics: proportion of SOMAs

occupied, proportion occupied by pairs, and

number of owls per SOMA. Because the sampling

(choice of stands) was random, average

effectiveness will be calculated forestwide and

statewide. Effectiveness will be evaluated as

follows: if on the average (over 3 years) 41 of

the 46 SOMAs were occupied by pairs and over the

3 years every SOMA surveyed was occupied by a

pair in at least 1 year, it would be concluded

that the SOMA system was working very well. The

conclusion has an implicit assumption that adult

owls have a life expectancy of more than 3

years, during which at least two young would be

produced. But if 23 of the 46 SOMAs were

occupied by pairs with 15 of 46 never occupied,

then effectiveness would be low and adjustments

(such as replacing the 15 never used with new

SOMAs) would be indicated.

Habitat descriptions will be compared to current

standards and guidelines to test their

appropriateness. These results could be used to

assess, and, if necessary, adjust the kind and

amount of land managed for spotted owls. It may

be possible to contrast the areas used by single

owls with the areas used by pairs. Thus,

definitive information on the habitat required

to maintain a population could be provided.

Coordination

The results of the monitoring program will be

augmented by research being done by the

Old-Growth Forest Wildlife Habitat Program and

the WDG. The Old-Growth Program is collecting

detailed information on the prey of spotted

owls, the structure and composition of young,

mature, and old-growth forests, the reproductive

attainment of adult spotted owls, and the

dispersal of juvenile spotted owls. The WDG has

been conducting a statewide inventory of spotted

owls, relating spotted owl distribution to land

use patterns, and studying adult owl habitat use

and juvenile owl dispersal. By the third year

of the monitoring program substantial new

information. relating to spotted owl management

will be available.

CONCLUSION

Federal regulations call for monitoring

populations of management indicator species.

Monitoring is a complex and costly procedure.

In Washington, Forest Service research, three

National Forests, the Pacific Northwest Region

of the National Forest System, and the Washington

Department of Game have collaborated in designing

and implementing a program for monitoring the

attainment of the Forest Service's objectives in

managing for spotted owls and for evaluating the

standards and guidelines to manage habitat for

spotted owls. Such collaborative efforts have

much promise and may be the only way to

accomplish effective monitoring of key sensitive

species. This monitoring system model is a

prototype for all monitoring in the National

Forest System; the level of investment, however,

must be matched to significance of the land use

issue for other species. 2/

ACKNOWLEDGMENTS

We thank Maureen Beckstead, Larry Brewer,

Richard Pedersen, Hal Salwasser, and Jared

Verner for their comments on an earlier version

of this paper.

LITERATURE CITED

Beckstead, Maureen. Olympic National Forest

spotted owl habitat management: translating

evolving management guidelines into actions.

In: Gutiérrez, Ralph J.; Carey, Andrew B.,

tech. eds. Ecology and management of the

spotted owl in the Pacific Northwest. Gen.

Tech. Rep. PNW-185. Portland, OR: U.S.

Department of Agriculture, Forest Service,

Pacific Northwest Forest and Range Experiment

Station; 1985: 14-20.

Carey, Andrew B. Monitoring diurnal,

cavity-using bird populations. In: Snag

habitat management: proceedings of a

symposium; 1983 June 7-9; Flagstaff, AZ. Gen.

Tech. Rep. RM-99. Fort Collins, CO: U.S.

Department of Agriculture, Forest Service,

Rocky Mountain Forest and Range Experiment

Station; 1983: 188-199.

Carrier, W. Dean. Planning and managing for the

spotted owl in the National Forests, Pacific

Southwest Region. In: Gutiérrez, Ralph J.;

Carey, Andrew B., tech. eds. Ecology and

management of the spotted owl in the Pacific

Northwest. Gen. Tech. Rep. PNW-185. Portland,

OR: U.S. Department of Agriculture, Forest

Service, Pacific Northwest Forest and Range

Experiment Station; 1985: 2-4.

2/ Personal communication, Hal Salwasser, U. S.

Department of Agriculture, Forest Service,

Wildlife and Fisheries Staff, 3825 E. Mulberry,

Fort Collins, CO.

37
Forsman, Eric D. Methods and materials for

locating and studying spotted owls. Gen. Tech.

Rep. PNW-162. Portland, OR: U.S. Department of

Agriculture, Forest Service, Pacific Northwest

Forest and Range Experiment Station; 1983. 8 p.

Forsman, Eric D.; Horn, Kirk M.; Neitro, William

A. Spotted owl research and management in the

Pacific Northwest. Transactions of the North

American Wildlife and Natural Resources

Conference. 47: 323-331; 1982.

Lee, Philip I. History and current status of

spotted owl (Strix occidentalis) habitat

management in the Pacific Northwest Region,

USDA-Forest Service. In: Gutiérrez, Ralph

J.: Carey, Andrew B., tech eds. Ecology and

management of the spotted owl in the Pacific

Northwest. Gen. Tech. Rep. PNW-185. Portland,

OR: U.S. Department of Agriculture, Forest

Service, Pacific Northwest Forest and Range

Experiment Station; 1985: 5-9.

MacCleery, Douglas W. National Forest System

land and resource management planning. Federal

Register. 47(190): 43026-43052; 1982.

Nelson, Robert D.; Black, Hugh, Jr.; Radtke,

Robert E.; Mumma, John. Wildlife and fish

management in the Forest Service: a goal

oriented approach. Transactions of the North

American Wildlife and Natural Resources

Conference. 48: 87-95; 1983.

Ruediger, William. Implementing a spotted owl

management plan: the Gifford-Pinchot National

Forest experience. In: Gutiérrez, Ralph J.;

Carey, Andrew B., tech eds. Ecology and

management of the spotted owl in the Pacific

Northwest. Gen. Tech. Rep. PNW-185. Portland,

OR: U.S. Department of Agriculture, Forest

Service, Pacific Northwest Forest and Range

Experiment Station; 1985: 10-13.

Salwasser, Hal; Hamilton, Carole K.; Krahn,

William B.; Lipscomb, James F.; Thomas, Carl

H. Monitoring wildlife and fish: mandates and

their implications. Transactions of the North

American Wildlife and Natural Resources

Conference. 48: 297-307; 1983.

Verner, Jared. An integrated system for

monitoring wildlife on the Sierra National

Forest. Transactions of the North American

Wildlife and Natural Resources Conference. 48:

335-366; 1983.

38
AN OVERVIEW OF RECENT RESEARCH

ON THE SPOTTED OWL

R. J. Gutigrrez

ABSTRACT: The recent literature on the northern spotted owl (Strix

occidentalis caurina) is reviewed and the salient features of the owl's

natural and life history are presented. The conclusion is that northern

spotted owls are dependent upon old-growth conifer forests of the Pacific

Northwest.

INTRODUCTION

-5?

The spotted owl (Strix occidentalis) occurs as

three recognized subspecies (S. o. caurina, S. o.

occidentalis, and S. o. lucida) distributed from

southern British Columbia south into Mexico

(American Ornithologists Union 1957). The

northern spotted owl (S. o. caurina) is thought to

be closely associated with old-growth Douglas-fir

(Pseudotsuga menziesii (Mirb.) Franco) forests

throughout the Pacific Northwest (Forsman and

others 1977, 1984; Gould 1974; Grinnell and Miller

-1944; Gutigrrez and others 1984; Solis 1983). The

importance of these forests to both the timber

industry and the spotted owl is the center of a

growing controversy over the disposition of oldgrowth forests and the future of the owl

(Heinrichs 1983, 1984).

Spotted owls appear to be declining with the

continued logging of old-growth forests (Forsman

and others 1977, 1982, 1984; Gould 1977, 1985;

U.S. Department of the Interior, Fish and Wildlife

Service 1982). Most of the remaining old-growth

areas occur in National Forests (Forsman and

others 1984; Gould 1979, 1985). The National

,.

-z Forest Management Act of 1976 (U.S. Laws, Statutes,

g.

R. J. Gutiérrez is associate professor and chairman of the Wildlife Department, Humboldt State

University, Arcata, Calif.

etc. 1976), which requires maintenance of viable

populations of vertebrate species on all National

Forests, is being invoked as a reason for intensive investigation and management of spotted owls

and other old-growth wildlife species (Carey 1984,

Carrier and others in press, Gutiérrez and others

1984, Ruggiero and Carey 1984).

In this paper, I will summarize the recent

research on northern spotted owls within the

context of natural history and life history

characteristics that are particularly important

for the management of this species. Campbell and

others (in press) have provided an extensive

bibliography on the spotted owl. I will therefore not attempt to incorporate obscure agency

reports unless they are particularly germane.

NATURAL HISTORY

General Comments

Prior to 1970, most observations and research on

spotted owls had been anecdotal (Campbell and

others in press), and the bird was thought to be

rare and secretive. Forsman (1976, 1980) was the

first to record extensive natural history observations of the spotted owl and to summarize usable

field study techniques (Forsman 1983). His work

was especially timely with passage of the

National Forest Management Act of 1976. In the

following natural history review I will first

present information on vocal and morphological

39
characteristics that have been found useful in

spotted owl studies. Then I will summarize salient

features of spotted owl habitat, home range and

movements, and food habits.

Vocalizations

Spotted owls are territorial and actively defend

their home range, particularly the nest grove

(Forsman 1976, 1980; Forsman and others 1984).

Thus, they can be located through imitation of

their calls. Males can be distinguished from

females by the male's lower-pitched, four-note

hoot (see Forsman and others 1984 for a more

complete description of the owl's vocal repertoire).

Molt and Sexual Characteristics

The molt of the spotted owl has been described by

Forsman (1981). Of particular interest to

biologists is the fact that three age classes can

be distinguished: juveniles can be identified by

the presence of downy plumage until about 3 months

postfledging; immature/subadult birds can be

distinguished by the presence of pointed, whitetipped middle rectrices from their first autumn of

life until midsummer of their third year; and

adults have rectrices with rounded tips. Barrows

and others (1982) describe a method for determining

the sex of spotted owls by retrix barring pattern.

Miller and Meslow (1985) have reported this method

to be accurate.

Females are, on the average, larger than males

(Earhart and Johnson 1970); however, the overlap

in weights, between large males and small females,

does not allow sexual determination. Similarly,

juveniles are usually at or near adult weight soon

after they are able to fly (personal observation);

thus weight cannot be used as a criterion for

either age or sex determination. Tail-barring

pattern may be the best future method for determining the sex of juveniles.

Habitat

Perhaps the most important contribution of recent

work has been the analysis of habitat and home

range (the latter will be discussed in the next

section). This information has been critical to

the delineation of appropriate habitat for Spotted

Owl Management Areas (SOMAs in the Pacific Northwest Region, USDA Forest Service) and Spotted Owl

Territories (SOTS in the Pacific Southwest Region).

Forsman and others (1984), Gutigrrez and others

(1984), Sisco and Gutigrrez (1984) and Solis (1983)

demonstrate a significant association of the owls

with old-growth forests. Solis' work is

particularly useful in that it describes not only

an affinity for old growth, but also describes the

forest structure in detail. Although Douglas-fir

old growth is-the most important habitat type,

much old growth (and mature, unmanaged conifer

forests) below the high elevation subalpine

conifers also is occupied by spotted owls

(Forsman and others 1984, Solis 1983).

Several interesting features of habitat use are

emerging from the studies. First, although

spotted owls can be found within second-growth c

conifer forest, and in other habitats, it is

unknown if they are reproductively successful;

this aspect needs further research (Forsman and

others 1977, 1984). Neither presence-absence nor :c

abundance of owls alone should be used as an

indicator of habitat quality (Van Horne 1983).

Fitness, when measured as breeding success, should

be used as one of the primary criteria for the

quality of habitat (Van Horne 1983). Second, not

all old- growth stands appear to be equally used by

the owls/ (Solis 1983). Use may be related 1

proximately to habitat structure per se, or

ultimately to food resources (see also Hilden 1965

for a theoretical discussion of these concepts).

Third, male and female owls appear to be using

habitat of different structure (Sisco and

Gutiérrez 1984, Solis 1983, see footnote 1).

In general, spotted owls use old-growth forests

that are characterized by multistoried stands of

large-diameter (> 91 cm in diameter at breast

height [d.b.h.]) conifers with hardwood understories in northwestern California. In Oregon,

the understory may be either hardwood or conifer

(Forsman and others 1984, p. 16). The stands in

California have high canopy closure (approximately

80-90 percent) and they are old (> 150 years) with

a high degree of stand decadence (Sisco and

Gutiérrez 1984, Solis 1983). Spotted owl habitat 3.

in Washington appears to closely resemble Cascade

Oregon habitats but has 90 percent canopy closure

(Garcia 1979).

Tables 1, 2. and 3 present data that more

specifically define the owl's habitat in northwestern California. The multistoried pattern of

spotted owl habitat is easily discerned from

tabulation of tree density and basal area (table

1). Douglas-fir dominates the upper canopy and

hardwoods the lower strata (that is, diameter

classes). There are, however, conifers and

hardwoods represented in all diameter classes.

A comparison of table 1 with table 2 shows the

average age of trees in the largest diameter

class (> 91 cm d.b.h.) is 268 years; the tree

diameter class 53-91 cm d.b.h. averaged 142 years.

There is much variation in ages among trees of a

particular size class as a result of the influence

of site factors, elevation, and exposure. Table

3 indicates that these stands also have a high

degree of decadence associated with them. Stands

used by spotted owls in northwestern California

may therefore contain relatively small diameter

(53-91 cm d.b.h.) trees but exhibit properties of

stands that are much older. Such properties ainclude (1) a multiple canopy of hardwoods and 9

1/

@

-Manuscript in preparation by David Solis, Wild- -

life Department, Humboldt State University,

Arcata, CA 95521.

40
Table l--Some tree characteristics within spotted

owl habitat in northwestern California 1/

Table 3--Summer habitat characteristics of 1/

spotted owl habitat in northwestern California

Diameter

size class 2/ Mean density Mean basal area

Habitat

characteristics Summer

Hardwoods:

I

II

III

IV

V

Subtotal 258.96 14.71

Conifers:

I

II

III

IV

V

Subtotal. 193.99 53.70

(Douglas fir) 171.73 49.65

Total trees 452.95 68.41

stems/ha m

2

/ha

46.20 0.48

154.14 4.40

47.54 5.26

9.80 3.27

1.26 1.30

17.98 0.18

74.47 2.27

48.28 5.68

25.67 9.81

27.57 35.74

1/ Data from Solis (1983) and Sisco and Gutiérrez

(1984) and represent 723 vegetation plots 0.02 ha

in size.

/Diameter size class: I = 10.16-12.44 cm d.b.h.

(diameter at breast height); II = 12.7-27.68 cm

d.b.h.; III = 22.94-53.08 cm d.b.h.; IV =

53.34-91.19 cm d.b.h.; V = >91.44 cm d.b.h.

Table 2--A sample of Douglas-fir (Pseudotsuga

menziesii) tree ages within spotted owl habitat

in northwestern California 1

/

Diameter 2

size class Mean- S.D. Sample size

years

I 47.3 13.0 3

II 51.8 8.5 5

III 114.1 57.2 70

IV 142.0 65.3 84

V 268.66 108.3 86

1/ Data is from Sisco and Gutiérrez 1984.

2/ Diameter size class : I = 10.16-12.44 cm d.b.h.

(diameter at breast height); II = 12.7-27.68 cm

d.b.h.; III = 27.94-53.08 cm d.b.h.; IV =

53.34-91.19 cm d.b.h.; V = >91.44 cm d.b.h.

Snag density

(stems/ha)

Canopy closure 2/

Decadence 3/

I

53.54

87%

.28

II .24

III .48

1/ Data are from Solis (1983) and Sisco and

Gutiérrez (1984) and represent 723 vegetation

plots, 0.02 ha in size.

-?-/Canopy closure is a measurement of both conifer

and hardwood components of the stand.

/Decadence : See Solis (1983) for a complete

description of decadence; however, level III has

highest snag incidence, indicating a more

decadent stand.

conifers and (2) advanced decadence including

dead and down debris and snags. Decadence plays

a very important role in spotted owl habitat.

First, suitable cavity nest sites are-formed as a

result of the decay and aging process. In

addition, snags, decadent and rotting trees, and

downed woody debris may provide cover and habitat

for flying squirrels and wood rats, the spotted

owl's major prey.

Removal of woody debris and understory vegetation

may alter the foraging patterns of spotted owls.

Solis (1983) reports that a radio-telemetered

bird foraged within a shelter-wood cut until the

understory was burned as part of a silvicultural

prescription. The owl was not observed to forage

in this area after the prescribed burn until the

understory vegetation had begun to grow again.

The pattern of habitat use in summer and in

winter is similar (Forsman and others 1984, Sisco

and Gutiérrez 1984). Winter habitats resemble

summer habitat structurally (Sisco and Gutiérrez

1984) in spite of the large -increases in winter

home range area (Forsman and others 1984, Sisco

and Gutiérrez 1984). Extensive analysis of plant

species composition and structural analysis of

northwestern California owl habitats is given by

Sisco and Gutiérrez (1984) and Solis (1983). The

old-growth habitat used by spotted owls are also

the most valuable timber on public lands in the

Pacific Northwest. One of the major questions

that managers and biologists ask is whether the

spotted owl is indeed dependent on old growth

41
(Carey 1984). There are several aspects of their

habitat ecology that strongly indicate that spotted

owls are dependent on old growth:

1. Habitat use patterns demonstrate the owl's

association with old growth (Foreman and others

1984, Forsman and Meslow 1985, Gutiérrez and

others 1984, Sisco and Gutiérrez 1984, Solis 1983;

see footnote 1).

2. Spotted owl habitat characteristics demonstrate

agreement between forest scientists and wildlife

biologists that this habitat is classified as old

growth (for example, Franklin and others 1981,

Franklin and Spies 1984, and reference immediately

above).

3. Habitat analysis demonstrates there is a

statistical difference in forest structure between

intensively used and available habitat (Solis

1983).

4. The decline of spotted owl populations as old

growth is logged demonstrates an association

between the owls and these particular forests

(Forsman and others 1984, U.S. Department of the

Interior, Fish and Wildlife Service 1982).

5. The correlation between home range size and

the amount of old growth in the range demonstrates

the importance of old growth in influencing home

range size (Sisco and Gutigrrez 1984; see footnote

1).

6. Spotted owl behavioral response to heat stress

by roosting in old growth demonstrates the

importance of old growth for thermoregulation by

owls (Barrows 1981).

7. The general absence of spotted owls on heavily

cutover lands demonstrates a qualitative, negative

impact on owl populations with loss of old growth

(Forsman and others 1977).

Home Range and Movements

Adult northern spotted owls are considered

sedentary animals (Forsman 1980, Forsman and

others 1984, Sisco and Gutiérrez 1984, Solis

19831, even though some populations show migratory

behavior (Layman 1985). In contrast, juvenile

spotted owls are highly mobile (Gutiérrez and

others 1985, Miller and Meslow 1985).

Movements within the home range usually do not

exceed 1.5 km (measured as straight distance from

beginning to end of sample period) within a 24-hour

period. Movements may, however, involve use of

large areas (about 300 ha) within a relatively

short period (3-4 weeks) (Forsman and others 1984;

see footnote 1).

One interesting aspect of the home range is that

it is large (x = 785 ha in Sisco and Gutiérrez

1984; x = 1713 ha, table 1, in Forsman and others

1984). Forsman and others (1984) state that an

average of 131 days of observation was needed to

determine 80 percent of an owl's home range area.

The data from northwestern California probably

underestimate the home range size for most of the

owls radio tagged there because the monitoring

period was less than 131 days. The owl's home

range often increases substantially in size with

winter range expansion (Forsman and others 1984,

Gutiérrez and others 1984, Sisco and Gutiérrez c

1984; see footnote 1). Home range size has been

shown to be positively correlated with the amount

of old growth within the range and not with other

seral stages (see fig. 13 in Sisco and Gutiérrez :s

1984). Owls in fragmented forests sometimes have

very large or very small home ranges relative to

other owls (Forsman and others 1982, 1984;

Gutiérrez and others 1984). Perhaps in the former

case the owls use larger areas to encompass fragments of old growth (Forsman and others 1984,

p. 54), and in the latter case they may be

isolated by adjacent territorial owls or are

constrained by inhospitable habitat (for example,

clearcuts and grasslands) (see footnote 1).

The relationship among home range size, habitat

dispersion, and habitat quality is still not well

understood (Gutiérrez 1985). Owls in fragmented

forests have limited access to old growth and may

have reduced fitness (lower reproduction); this

needs to be studied (Gutiérrez 1985). There is

some indication that some owls with only limited

old growth available to them have low reproductive

output. 2/

Food Habits

Although spotted owls capture a variety of prey, :!I:

numerous food habit studies have shown that mammals

are their major food resource--particularly flying

squirrels, Glaucomys sabrinus, and woodrats,

Neotoma sp. (Barrows 1980, 1985; Forsman and 2

others 1984; Kertell 1977; Marshall 1942; Solis

1983). Earhart and Johnson (1970) suggest that

spotted owls are more insectivorous than current

data indicate. Forsman and others (1984) and

Sisco 3/ believe that flying squirrels may predominate in the diet of owls living in mesic

habitats and woodrats may predominate in more

xeric environments. Habitat structure or food

availability within these habitats may influence

which prey species is most abundant. It is

interesting that woodrats in northwestern

California have a bimodal distribution of

abundance; their greatest populations are found

in early and late seral stage forests (that is,

brushy clearcuts and old-growth forests) and the

lowest populations are found in intermediate-aged

forests (Raphael and Barettt 1984).

Barrows (1985) presents data that suggest spotted

owls may breed in years when their larger prey

2/ Unpublished data by R. J. Gutiérrez and others

on file, Wildlife Department, Humboldt State

University, Arcata, CA 95521.

3/ Manuscript in preparation by C.

;q.d

Sisco, Wildlife

Department, Humboldt State University, Arcata,

CA 95521.

42
are either more abundant or more available.

Barrow&/has data on Peromyscus populations in his

study area that suggest spotted owls do not appear

to be tracking large Peromyscus populations. His

idea is certainly plausible when one observes the

large talons these birds possess. The large talons

indicate evolutionary selection for handling large

prey. The ecology of the spotted owl's major prey

is not well understood but may ultimately be

important in predicting reproductive biology and

demography of the spotted owl (Gutiérrez 1985).

LIFE HISTORY

Little is known of the demography or other life

history characteristics of spotted owls. Studies

of population dynamics require the construction of

life tables. Although spotted owl demographic

data are limited to first approximations, subject

to modification with new information, life table

construction is possible (Barrowclough and Coats

1985). In the following brief review I will

describe those life history features that are

particularly important to the demography of

spotted owls.

Reproductive Biology

There is substantial yearly and geographic variation in the proportion of an owl population that

breeds (Barrows 1985, Forsman and others 1984,

Gutiérrez and others 1984, Laymon 1985).

Gutiérrez and others (1984) report general

breeding failure throughout the Pacific Northwest.

Forsman and others (1984), in analyzing 130 nesting

attempts over 5 years, found on the average that

62 percent (range, 16-89 percent) of their pairs

attempted to nest each year but Gutiérrez and

others (see footnote 2) have noted a lower

frequency of nesting attempts in northwestern

California. They found an average of 36 percent

of 92 pairs (range, 0-45 percent) attempted to

nest over a 3-year period. Some pairs appear to

nest far more frequently than others; for example,

Miller (1974) reports a pair, (presumably the same

birds) that nested in 5 of 7 years. Conversely,

Barrows (see footnote 4) and Gutiérrez and others

(see footnote 2) have monitored some nonnesting

pairs for 5 years. These unsuccessful pairs were

located in nonold-growth habitat or in fragmented

habitat. Reproductively successful pairs may

provide clues for isolating habitat quality or

individual variation parameters responsible for

that success. Yet Forsman and others (1977)

correctly point out the need to study those few owls

in second-growth forests (see also Gutiérrez 1985).

Clutch Size

The modal clutch size was two in Forsman and

others (1984). They refer to other historical

4/ Unpublished data by Cameron Barrows on file,

North Coast Preserve, Banscomb, CA 95417.

studies that report four-egg clutches although

the maximum brood size (an index to clutch size)

they observed was three. Forsman and others

(1984) found no evidence for renesting by wild

spotted owls, although captive birds have laid

two clutches in one season (Forsman and others

1984). Because the birds are physiologically and

genetically capable of laying two clutches,

failure to renest may be related to food availability or some other factor.

Because males feed their incubating mates, females

are dependent on the male's foraging ability

(Forsman 1976). When foraging conditions are poor

and the female is forced to leave the nest to

search for food, the clutch may be lost. Poor

food resources probably do not improve soon enough

to allow a female to renest.

Age At First Reproduction

Barrows (1985) reports a second-year female

breeding and Miller 5/ has observed a second-year

female breeding. My field crew has also observed

at least two second-year females paired with

adult males. Because juveniles have a high

mortality rate, second-year breeding, at least by

females, may not be uncommon.

Survivorship And Mortality

Juvenile owls have a low first-year survivorship

(Forsman and others 1984, Gutiérrez and others

1985, Miller and Meslow 1985). Young Strix owls

die for many documented reasons, such as avian

predation, starvation, accidents, and human

predation (Gutiérrez and others 1985, Southern

1970). Young spotted owls are especially

vulnerable during development following fledging

and during early dispersal (Forsman and others

1984, Gutiérrez and others 1985, Miller and

Meslow 1985).

Forsman and others (1984) suggest that spotted

owls are long lived. Data on adult demography

will be slow in accumulating and will require

extensive banding and monitoring to determine

adult survival rates. Adults are susceptible to

predation, starvation, disease, and accidents,

but the influence of these forces on survival is

unknown.

Density

There are few published accounts of density

estimations in the strict sense of the term

(Burnham and others 1980). Forsman and others

(1977) published an "index of density," and

Marcot and Gardetto (1980) published nearest

neighbor distances and other estimates

5/ Manuscript in preparation by Gary Miller,

Oregon Cooperative Wildlife Research Unit, Oregon

State University, Corvallis, 97331.

43
of density. The assumptions and applications

of nearest neighbor distance has been

discussed by Clark and Evans (1954) and Poole

(1974). This technique is unsuitable for

demographic (density) analysis. Barrowclough and

Coats (1985) approximate the density of spotted

owls across all habitats to be 0.037 owls/km2

(based on calling surveys compiled by the

California Fish and Game Department).

Population boundaries need to be delineated to

arrive at some area suitable for census. I would

predict spotted owl densities are likely to vary

substantially with habitat quality and quantity.

Forsman and others (1977) found spotted owls

substantially more abundant (approximately 12 times,

according to their index) in old growth than in

second growth. One of my study areas of 10,000 ha

has 22 owls and a nearby area with good census

data has 12 owls in 20,000 ha. The latter area

has undergone extensive logging.

Dispersal

Dispersal ecology has been the subject of recent

intensive research (Gutiérrez and others 1985,

Miller and Meslow 1985). Preliminary results show

that juvenile spotted owls are aggressive dispersers

capable of moving long distances. They appear to

move directionally and rapidly (Gutiérrez and

others 1985). It is unknown from published data

whether this pattern is consistent with other

areas (Allen and Brewer 1985, Miller and Meslow

1985). Observations of the 1984 cohort of

juvenile spotted owls in northwestern California

suggest that this pattern may not continue (see

footnote 2). As dispersal data continue to

accumulate, managers will gain a critical piece of

information for spatially distributing spotted owl

territories and calculating demographic parameters

for spotted owls (Barrowclough and Coats 1985).

Other Life History Features

Some important parameters of life history evolution

are almost entirely unknown for spotted owls but

ultimately may play a role in predicting the effect

of management plans on the owls. Some of these are

their interspecific competitive ability, variation

in parental care among pairs, environmental

stability, and population genetics (see also

Stearns 1976, 1977, for a discussion of life

history characteristics).

HYPOTHESES ON DEPENDENCE ON OLD GROWTH

Recent research has led to some interesting

hypotheses concerning the spotted owl's

dependence on old-growth forests. These

hypotheses are:

1. Nesting hypothesis,

2. Thermoregulation hypothesis,

3. Predation hypothesis,

4. Prey hypothesis, and

5. Adaptation hypothesis.

Carey (1985) discusses these hypotheses elsewhere

in this symposium. I have combined his two

hypotheses on prey under one category because

they are often interrelated. The implications of

these hypotheses for management will be discussed

as will their potential for explaining the $

evolutionary relationships of spotted owls and

old-growth forests. It is undoubtedly a combination of factors that have led to the spotted

owl's role or dependence on old-growth forests.

I have, therefore, expanded and reinterpreted

%

Carey's (1985) adaptation hypothesis.

Nesting Hypothesis

Spotted owls, like most other owls, do not

construct their own nests (Burton 1973). They

depend on the natural occurrence of suitable

nesting sites within their habitat. The location,

structure, and type of nesting sites used by

spotted owls are typically found in old, decadent

forests (Forsman and others 1984). They are

generally high above the ground (Z = 27.3 m;

x = 24.3 m); in cavities or broken-top snags (64

percent; 92 percent); and in large diameter trees

(x = 135cm d.b.h.; x = 170cm d.b.h.)

and others 1984 and LaHaye,- respectively). 6/

(Forsman

Old-growth forests are often decadent and provide

the greatest number of trees suitable for nesting

sites. It is unlikely that the need for nesting

sites is the evolutionary force behind the

dependence of spotted owls in old-growth forests

for the following reasons. First, spotted owls

do nest in abandoned stick nests built by other 3:

birds and in accumulations of organic debris in

the tree canopy. Forsman and others (1984)

report 36 percent of their spotted owl nests were

of debris or were nests of other species. Both 2

of these conditions can occur in younger aged

forests, although accumulations of organic debris

probably occur more frequently in old-growth

forests (Forsman and others 1984). ‘Second,

residual, decadent trees are often left behind

after fires or other natural environmental

perturbations. Yet, spotted owls apparently

seldom use these residual old-growth trees in

younger forests (only 6 percent of the nests

found by Forsman and others 1984, p, 30, were in

young forests with scattered residual trees).

Finally, open-canopied hardwood stands within

old-growth areas often provide presumably suitable

structural nest sites but are rarely used by

spotted owls (see footnote 6).

From a management perspective, nesting sites can

probably be created through manipulation. Live

trees can be topped or cavities created in

several ways to create structurally suitable

nesting sites (see footnote 6). One pair of owls

has been observed to use an artificial cavity in

the Six Rivers National Forest (personal observa- r

tion). The tawny owl (Strix aluco) of Europe 5

- -

responds readily to artificial nest boxes

6/M.S. thesis in progress by W. LaHaye, Humboldt

State University, Arcata, CA 95521.

44
(Southern 1970). Nest boxes have been placed in

old-growth forests in California by Forest Service

biologists without success (personal observation).

The sites chosen for box placement may have already

had abundant or traditional nesting sites. For

3 example, my research crew discovered an active owl

nest within 150 m of a nest box after the box had

been placed in an old-growth tree. Because this

pair had successfully nested in 2 out of 4 years

ri at the natural site, it was unlikely that they

would abandon their traditional site for the

artificial one. The successful placement and

construction of nesting boxes will depend heavily

on adequate models of nesting sites and nesting

habitat (see footnote 6).

Thermoregulation Hypothesis

Barrows and Barrows (1978) and Barrows (1981) first

quantified the relationships between roosting site

microclimate and heat stress in spotted owls.

Spotted owls choose cool and shady microclimates

that provide relief from high ambient temperatures

(Forsman 1976, Solis 1983).

Because natural selection has favored the evolution

of a plumage that is adapted to withstand winter

conditions (Barrows 1981, Barrows and Barrows

1978), it is possible that use of the cool microclimate, which multistoried old-growth forests

provide, is the counterbalance to the plumage.

There are, however, several natural history

observations that suggest that even though

B- selection for old-growth roosting sites may be an

indication of dependency on old-growth forests, it

probably does not explain the dependency on large

tracts of old growth.

p

Ward 7/ analyzed microhabitat selection and

behavioral positioning in response to variation in

ambient temperatures. He concluded that the

position an owl chooses within the foliage is as

important as the selection of actual roosting

habitat. Sisco and Gutiérrez (1984) demonstrate

that the old-growth forests are still the most

important habitats for spotted owls when heat is

not a factor. Alternatively, old-growth forests

may provide more protection from inclement weather

and, thus, may be important for winter thermoregulation (Forsman and others 1984).

This hypothesis is important to management.

Spotted owls need adequate thermal cover in all

seasons. Many areas of potential spotted owl

habitat may not provide relief from heat without

old-growth. In some areas access to old-growth

roosting sites may energetically constrain the

owls to a finite distance from the roosting site.

Because owls can and do select roosting sites in

cool, moist, shaded canopies within canyons to

relieve heat stress, they may have some alternative

& habitats to use. Also, the small patches (24 ha)

Fi

7/ Unpublished senior thesis by J. P. Ward on file,

Department of Wildlife, Humboldt State University,

Arcata, CA 95521.

of old-growth forest required as a minimum patch

size for spotted owl management areas in California

will probably provide an adequate microclimate to

relieve heat stress. Yet SOMAs and SOTS without

old growth on south-facing slopes or in areas

where alternative habitats are not located will

probably not be used by spotted owls.

Predation Hypothesis

Great horned owls (Bubo virginianus) and goshawks

(Accipiter gentilis) will prey on juvenile spotted

owls (Forsman and others 1984, Gutiérrez and

others 1985, Miller and Meslow 1985; see footnote

1) . Presumably, spotted owls are more vulnerable

in open habitats than in the forests. The many

observations of juvenile spotted owls moving

through open areas (that is, grasslands, savannas,

clearcuts, and oak woodlands) (see Gutiérrez and

others 1985) suggest that the potential for predation does not, in general, deter these birds

from using open areas when they are juveniles.

Forsman and others (1984, p. 54) suggest adult

spotted owls may also be preyed upon by great

horned owls. Yet great horned owls are found

throughout the range of spotted owls and often

occupy areas adjacent to or overlapping spotted

owl home ranges with little predation occurring

(personal observation). I have recorded spotted

owls temporarily avoiding an area when a great

horned owl vocally established its presence, but

the birds again used the area at some later date.

Thus predation has probably occurred opportunistically at low levels for adults and at higher

levels among juvenile spotted owls. This predation pressure has probably not been strong enough

to explain the spotted owl's association with

old-growth forests.

From a management point of view, predation could

become a serious factor. If great homed owls

increase in response to forest fragmentation,

then the opportunity for their preying upon

spotted owls will increase.

Prey Hypothesis

I have chosen to combine the prey abundance and

prey availability hypotheses of Carey (1985) and

Forsman and others (1984) into one hypothesis

because I believe the hypotheses are closely

related.

Raphael and Barrett (1984) suggest a bimodal

abundance distribution for wood rats in northwestern California. These rodents are plentiful

in shrub-sapling stages and in older aged forests.

Raphael and Barrett (1984) demonstrate an

increase in relative abundance of wood rats with

increasing age of old-growth stands. Thus the

spotted owl's primary prey, in northwestern

California, is more abundant as the forest

increases in age.

The reason that owls do not forage in shrubsapling habitats probably is the inability of the

owls to hunt effectively in these densely vegetated habitats (Forsman and others 1984). Solis

45
(1983) and Sisco and Gutiérrez (1984) demonstrate

significant differences in foraging habitat between

male and female owls. The differences in the

structure of foraging habitat is probably related

to-the wing loading of the birds. The smaller,

more maneuverable males use denser forests.

Differential habitat use by the sexes may reflect

an avoidance of competition. These differences

persist in winter when home ranges expand and the

birds forage independently (Sisco and Gutiérrez

1984, see footnote l). Because shrub-sapling

stages are far more dense than habitats normally

used by foraging owls, one might expect that the

owls cannot maneuver well enough therein to

effectively prey on wood rats. Although Raphael

and Barrett (1984) did not adequately sample

flying squirrels, these animals are rare in

shrub-sapling stages and in pole-sized timber.

The ecology of wood rats and flying squirrels

within Pacific Northwest forests is not well

understood. If their populations fluctuate

asynchronously, or by habitat type and age, then

it would help explain not only the foraging of

owls within large areas but also the owls' use of

a variety of stands greater than 150 years of age.

Hilden (1965) points out that food is one of the

ultimate factors in habitat selection of a

species, not only because of short-term

physiological maintenance but also because of

reproductive needs. It is probably the interplay

of abundance, availability, and distribution of

the spotted owls food base that explains the birds

historical dependence on large tracts of old-growth

forests. As its habitat becomes increasingly

fragmented, the bird's needs for thermoregulation,

for nest sites, and to avoid predators and

competitors will become more important factors in

the population ecology of spotted owls.

The prey hypothesis is probably the most important

hypothesis for managers because it may explain the

spotted owl's use of large tracts of old-growth

forest. If the owl's major prey is geographically

variable in abundance, distribution, or availability, spotted owls may have to forage widely

through the year to find adequate prey populations.

Thus the increased energy needed to exploit habitat

patches in a fragmented forest may negatively

affect reproductive output. The interrelationship

between prey, territory size, and foraging patterns

needs to be investigated to predict the impact of

habitat fragmentation on the species (see also

Gutiérrez 1985).

Adaptation Hypothesis

Carey (1985) discusses this hypothesis, which

proposes that spotted owls have coevolved with

old-growth forest and thus are behaviorally or

physiologically adapted to these forests. In

reality, this hypothesis is a combination of all

other hypotheses and unknown natural selection

forces. I will expand this hypothesis differently

than does Carey (1985).

Biologists could engage in endless discussion over

the coevolution of spotted owls and old-growth

forests. Spotted owls may have even secondarily

invaded old-growth forests although this is

unlikely. Nevertheless, there is considerable

data, just presented, that old-growth is important

if not critical for thermoregulation, nesting, and

foraging. Although ecologists are currently a. .&

engaged in serious debate concerning the nature

of competition (Salt 1984), one potential factor

in the relationship of old growth and spotted owls

might have been the competitive relationship with

the larger and more widespread and aggressive 'F

great horned owl. One potential way of avoiding

competition is through differential habitat use.

Through time the spotted owl's success in using

old growth may have favored adaptive response to

old-growth habitation regardless of the original

pressure to use old growth. Forest fragmentation

in the Pacific Northwest may also favor the

spread of a potential competitor in the barred

owl (Strix varia) (Gutiérrez and others 1984,

Taylor and Forsman 1976). The interaction of

these closely related species is now being

studied by Allen. 8/ Introducing competitors, as

well as changing the nature of the environment

spotted owls have shown strong adaptive responses

to, could have serious consequences for spotted

owls. Studies of spotted owls and their repro--

duction under varying environmental conditions

will help tremendously in understanding the

nature of the spotted owl's adaptability in a

changing world.

CONCLUSIONS 73;

Wildlife biologists have gained a great deal more

information on the natural history than on the

demography of the northern spotted owl. There are ,=,

several reasons for this. First, natural history p

data are needed to establish a research foundation;

second, natural history features are more easily

observed in nature and often require only direct

observation; third, natural history information

provides the manager with the raw data for

management (for example, habitat requirements and

nest site selection). Life history characteristics provide the manager with the tools

necessary for developing predictions of population viability. Many life history features,

particularly demographic and, to a lesser extent,

dispersal information, take a great deal of time,

energy, and money to quantify. Barrowclough and

Coats (1985) and Shaffer (1985) point out the

importance of this information for predicting the

long-term viability of spotted owls. The need

for specific research is outlined elsewhere in

this symposium by Gutiérrez (1985).

Old-growth forests provide the food and cover

essential for the survival and breeding success

of northern spotted owls. The impact of habitat

loss through logging over time must be assessed a^

8/ Manuscript in preparation by H. Allen,

J2-

Washington Department of Game, 600 North Capitol

Way, Olympia, WA 98504. .

46
both in terms of natural and life history characteristics. Clearly habitats with known,

consistently reproductive pairs must be chosen as

the SOMA. The ultimate numbers of owls to be,

maintained will depend upon demographic and

dispersal information that-is, at present, lacking.

First order approximations are possible (Barrowclough and Coats 1984) but will undoubtedly change

as our understanding of the spotted owl increases.

ACKNOWLEDGMENTS

I would like to thank Cameron Barrows, Andy Carey,

Sadie Coats, Alan Franklin, Ann Franklin, Ned K.

Johnson, William LaHaye, Bruce Marcot, David

Solis, and James P. Ward for critically reviewing

this paper.

LITERATURE CITED

Allen, Harriet; Brewer, Larry W. A review of

current northern spotted owl (Strix occidentalis

caurina) research in Washington State. In:

Gutiérrez, Ralph J.; Carey, Andrew B., tech. eds.

Ecology and management of the spotted owl in the

Pacific Northwest. Gen. Tech. Rep. PNW-185.

Portland, OR: U.S. Department of Agriculture,

Forest Service, Pacific Northwest Forest and

Range Experiment Station; 1985: 55-57.

American Ornithologists Union. Checklist of North

American birds. Baltimore, MD: The Lord Baltimore

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49
BREEDING SUCCESS RELATIVE TO FLUCTUATIONS IN DIET

FOR SPOTTED OWLS IN CALIFORNIA

Cameron W. Barrows

ABSTRACT: This paper describes infrequent, successful breeding in spotted

owls (Strix occidentalis) and the relationship between breeding and diet.

When spotted owls do breed, large prey such as dusky-footed woodrats and

flying squirrels are predominate in their diet. The availability of these

large prey items may be important in the breeding frequency and success of

spotted owls. The relationship between breeding success and prey

populations should be considered in the development and implementation of

habitat-suitability models for spotted owls.

INTRODUCTION

Recently there has been a substantial growth in

the knowledge of spotted owl (Strix occidentalis)

habitat requirements. Forsman's work in Oregon

(Forsman 1976, 1980) provides an initial foundation for spotted owl research. For northern

California, Solis (1983) and Sisco and Gutiérrez

(1984) provide detailed analyses of seasonal

habitat use by spotted owls. Barrows and Barrows

(1978) and Barrows (1981) describe microhabitat

selection related to the owls' thermoregulatory

constraints.

Data from the studies mentioned above have been

incorporated into spotted owl management plans

by the USDA Forest Service and used to develop

habitat suitability models (Laymon and Barrett

1982). There remains a serious void in knowledge

about spotted owl habitat that precludes a wellinformed application of these plans and models.

For example, the factors that influence the

reproductive success of spotted owls are poorly

understood. Forsman (1976) first described the

irregular breeding of spotted owls. Although

CAMERON W. BARROWS is a preserve director at the

Northern California Coast Range Preserve, The

Nature Conservancy, Branscomb, Calif.

Barrows (1980) alludes to mechanisms responsible

for breeding irregularity in spotted owls, the f

causative factors are not documented.

In this paper, I present results of ,a study

designed to examine the causes of the lack of

successful breeding in spotted owls. It should

be noted that this is a multifaceted problem and

only one aspect is examined here.

Newton (1979) has shown that breeding rates in

raptors are positively correlated with food

suPPlY- Most studies examining this relationship

have dealt with relatively simple predator-prey

systems consisting of a single primary prey

source (Adamick and others 1978, Hamerstrom 1979,

Pitelka and others 1955, Smith and others 1981).

Spotted owls take a broad spectrum of prey

(Barrows 1980); any one of four major mammalian

prey species can be the most prevalent in the

owls' diet in a given year. My analysis examined

the relationship between fledging success and the

relative frequency of these mammalian prey

species in the diet of spotted owls.

5

METHODS AND STUDY AREA

I collected regurgitated pellets below diurnal

roost sites of spotted owls during 1977 through $

1984. The pellets contained approximately 1,500

individual prey items. To facilitate comparisons

over much of the spotted owls' range in

50
California, I categorized prey species into two

size groups: small prey -- animals that weigh

less than 100 g, and large prey -- animals that

weigh 100 g or more. Only mammalian prey were

considered in this grouped analysis because

23: mammals comprise over 90 percent of the biomass

consumed by spotted owls (Barrows 1980). I also

calculated mean prey weight of all prey species

for each of my study areas.

For this study, I defined fledging success as the

percent of occupied territories in each area in

which spotted owl pairs fledged young over the 8-

year period. Each year I observed owls in a

territory was designated a potential breeding

attempt. I recorded 47 breeding attempts in 21

spotted owl territories. Five of these

territories were found in the Peninsular Range of

southern California; the other 16 territories

were located in Marin, Mendocino, Humboldt and

Trinity Counties of northern California. My

largest sample came from three occupied

territories observed for 4, 6, and 7 years (17

breeding attempts) in The Nature Conservancy's

Northern California Coast Range Preserve in

Mendocino County.

RESULTS AND DISCUSSION

Forsman and others (1984) record spotted owl

fledging success for Oregon over a 5-year period

(1972-1976). They observed 130 breeding attempts

with a fledging success of 44 percent. My data

e- from California were similar with 47 breeding

attempts over 8 years and a fledging success of

45 percent. Individual territories varied

considerably in fledging success. Three terri5. tories in northern Mendocino County had a fledging

success of 0 percent, 33 percent, and 29 percent,

for 4, 6, and 7 years, respectively. One territory in central Humboldt County had a fledging

success of 100 percent based on 6 years of

observation. Barrett and Laymon (1982, 1983)

report a fledging success of 6 percent based on

32 breeding attempts over 2 years in the Sierra

Nevada of California. Miller (1974) reported a

fledging success of 80 percent in 5 years of

observation of one territory in Marin County,

California.

The generally low and variable fledging success of

spotted owls shows marked yearly trends. A broad

regional failure in spotted owl breeding success

was observed in 1982 (Gutiérrez and others 1983).

Fledging success approached 0 percent for Oregon

1/ (Miller and Meslow 1984) and northern California.-

Breeding success improved in 1983. Of 63 occupied

territories checked in Oregon, 48 percent

successfully fledged young; on those territories

with known pairs of owls, 62 percent successfully

P

fledged young (Miller and Meslow 1984). In

northern California in 1983, 17 percent of 87

occupied spotted owl territories successfully

Table l--Percent occurrence of prey species in

regurgitated pellets of spotted owls, collected

from two owl territories in California

AREA/PREY SPECIES 1977 1980 1981 1982 1983

--- - Percent - - - - -

Northern Coast Range A 1/

*

Neotoma fuscipes 43 14 8 16

Glaucomys sabrinus 17 8 3 32

Arborimus longicaudus 9 35 50 32

Peromyscus maniculatus 9 20 26 8

Nonmammalian 

Other mammalian prey 2/ 1 3 0 1

prey 

3/ 21 20 13 11

Northern Coast Range B

*

Neotoma fuscipes - -

Glaucomys 

Arborimus long

Peromyscusmanicul

_-- 18 18 14 9 3

sabrinus 13 18 29 16 24

icaudus 24 32 20 38 42 -

tatus 15 12 10 14 14

Other mammalian prey 4 3 7 7 2

Nonmammalian prey 26 17 20 16 15

1

/Northern Coast Range A and B are located on

the Northern California Coast Range Preserve,

Mendocino County, CA.

2/ Other mammalian prey include: Clethrionomys

californicus, Microtus californicus, Scapanus -._. ..- - _

latimanus, Neurotrichus gibbsi, Sorex

trowbridgii, Lasiurus cinereus, Mustela erminea,

Tamias sp., and Sylvilagus sp.

3/ Nonmammalian prey include various species of

arthropods and birds.

* Indicates year of successful breeding.

fledged young; of those territories with

confirmed pairs, 45 percent successfully fledged

young (Gutiérrez and others 1984). Similar year

to year fluctuations were noted by Forsman and

others (1984).

The year to year variations in the diet of

representative pairs of spotted owls are shown

in table 1. An increase in the frequency of

large prey in the diet during breeding years was

characteristic for all of the pairs of owls

included in the analysis. Overall mean prey

weights for breeding spotted owls (x = 115 g,

S.D. = 31) are significantly greater (one-tailed

t test, P(O.01) than for nonbreeding owls (x =

79 g, S.D. = 25) for 16 spotted-owl pairs I

studied intensively. A comparison of the

frequency of spotted owl prey species, grouped

by size, taken in breeding and nonbreeding years

is depicted in figure 1.

1/ Personal communication, R. Gutiérrez, Humboldt

State University, Arcata, CA 95521.

51
4 

Peninsular Ran 

Northern Coast Range 

Figure 1. Prey frequencies in the diet of four representative pairs of breeding and nonbreeding 

spotted owls. Successful breeding years are denoted by an "X" above the histogram. Mammalian 

prey are grouped in two size classes; small prey -- less than 100 g; large prey -- 100 g or more. 

(Northern Coast Range pairs A and B are located on the Northern California Coast Range Preserve, 

Mendocino County, CA; Peninsular Range pairs A and B are located in Cuyamaca Mountains State Park, 

San Diego County, CA). 

Differential breeding success rates in spotted 

owls may relate to basic habitat quality and 

varying habitat conditions. Habitat features, 

such as shrub cover, snag density, volume of dead 

and down wood, and canopy cover, are correlated 

with prey density and vulnerability (Maser and 

others 1979, Southern and Lowe 1968). These 

characteristics vary through the forest and so 

might account for some interterritorial 

differences in spotted owl breeding success. 

Fruit and mast production and weather-related 

effects on prey vary among years and sites. 

Food supply is most often cited as the ultimate 

cause in determining breeding success in raptors 

(Newton 1979). Other factors such as the individual owl's breeding experience certainly have 

some effect (for example, see Southern 1970); in 

at least one case, however, 1 found a second-year b 

female spotted owl successfully breeding. Small 

mammal density estimates for northern California 

52 
2/ in 1982 and 1983- support a correlation between

breeding success of spotted owls and fluctuations

in rodent populations. This correlation must be

viewed with skepticism as the primary prey species

of spotted owls in northern California (Barrows

1980) are not sampled effectively by a single

trapping method, Dusky-footed woodrats (Neotoma

fuscipes), northern flying squirrels (Glaucomys

sabrinus), red tree voles (Arborimus longicaudus),

and deer mice (Peromyscus maniculatus) are

important prey of spotted owls, but their

dissimilar ecologies and behaviors require vastly

different sampling methods for estimating their

densities. Often densities can't be estimated

and population indices are not comparable among

species.

The energetic demand on a spotted owl pair feeding

one to three owlets has not been measured but it

must be considerably greater than that for

nonbreeding pairs. The average weight of duskyfooted woodrats (269 g) or northern flying

squirrels (115 g) (Forsman and others 1984) is

four to twelve times that of deer mice (22 g) and

red tree voles (27 g). The energetic benefits of

taking larger prey, which require fewer trips to

the nest, must be balanced against possible costs,

such as greater difficulty of capture and a lower

encounter rate, that result in longer search times

for these larger animals.

For the spotted owl pairs I studied, the presence

of large prey, such as dusky-footed woodrats and

northern flying squirrels, is important to

breeding success. The high frequency of large

prey in the diet of breeding spotted owls could be

a function of either the availability of the large

prey or the owls' prey selection. Prey availability, however , partly determines prey selection.

This distinction is important but is beyond the

scope of the present paper. Understanding the

ecology of the prey is fundamental to

understanding the ecology of the predator. For

the spotted owl, predator-prey relationships seem

closely linked to reproductive success. Managing

for spotted owls, therefore, should include

consideration of those animals that serve as owl

prey; ecological data on these prey species is

required before we can understand the process

behind the breeding pattern of spotted owls,

Current spotted owl management plans and habitat

suitability models focus on habitat use by spotted

owls, not on the owls' productivity. Habitat use

alone is but one measure of habitat quality (Van

Horn 1983). Breeding success is perhaps the best

measure of habitat quality (Hilden 1965).

Individual spotted owls and spotted owl pairs do

occupy habitats that are apparently inadequate

for consistent successful reproduction. Without

immigration from areas that allow high

----ll___-

2/ - Personal communication, Martin Raphael,

University of California, Berkeley, CA 94720.

Unpublished data on file, Northern California

Coast Range Preserve, 42101 Wilderness Road,

Branscomb, CA 95417.

reproductive output, spotted owl populations in

poor environments may not be able to persist.

Habitat suitability models for spotted owls

need to be tested using the frequency of

successful breeding, Such tests could be

conducted by applying the models to the

territories of pairs for which reproductive

attainment has been measured. If the models

cannot distinguish between the territories of

reproducing and nonreproducing owls in terms of

viability, then the models must be reexamined

and refined. The models could also include

terms reflecting the suitability of the territory

for the owls' major prey species. The importance

of regular breeding success in a population

cannot be overstated. Factors that contribute

to breeding success should be integral parts of

habitat models. Such factors may vary

temporally (for example, density) and long-term

ecological studies may be necessary before good

models can be developed.

ACKNOWLEDGMENTS

Katherine Barrows, Bill Block, Lenny Brennan,

Andrew Carey, Rocky Gutiérrez, Pat Manley, and

David Solis offered critical suggestions that

improved this paper. Katherine Barrows, Alan

Franklin, Rocky Gutiérrez, Bill LaHaye, and Pat

Ward augmented my prey analysis with numerous

owl pellets collected from throughout northwestern California.

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State University; 1983. 230 p. M.S. thesis.

Gutiérrez, Ralph J.; Franklin, Alan; LaHaye,

William S.; Meretsky, V.J.; Ward, J.P. Juvenile.

spotted owl dispersal: progress report #4 (16

November 1983 to 15 June 1984). Arcata, CA:

Humboldt State University Foundation, Humboldt

State University, 1984. 7 p.

Southern, H.N.; Lowe, V.P.W. The pattern of

distribution of prey and predation in tawny

owl territories. Journal of Animal Ecology.

37: 75-97; 1968.

Southern, H.N. The natural control of a

population of tawny owls (Strix aluco).

Journal of Zoology, London. 162:197-285;

1970.

Hamerstrom, Francis N. Effect of prey on

predators: voles and harriers. Auk. 96(2):

370-374; 1979.

Hilden, 0. Habitat selection in birds, a review.

Annals Zoologica Fennica. 2: 53-75; 1965.

Laymon, Stephen A.; Barrett, Reginald H. Administrative study of relationships between

wildlife and management of mature and overmature

(old-growth) tree stands: supplemental report

on a test of a spotted owl habitat suitability

model. Berkeley, CA: U.S. Department of

Agriculture, Forest Service, Pacific Southwest

Forest and Range Experiment Station; 1982. 31 p.

Maser, Chris; Anderson, R.C.; Cromack, Kermit,

Jr.; Williams, J.T.; Martin, R.E. Dead and

down woody material. In: Thomas, Jack Ward,

ed. Wildlife in managed forests - Blue

Mountains of Oregon and Washington. Agric.

Handb. 553. Washington, DC: U.S. Department

of Agriculture, Forest-Service; 1979: 78-95.

Miller, Grace M. Grace Miller on spotted owls.

In: Walker, L.W., ed. The book of owls. New

York, NY: Alfred A. Knopf; 1974: 130-146.

Miller, G.S.; Meslow, E. Charles. Juvenile

spotted owl dispersal project: 1983 annual

report (April 15, 1983 - January 31, 1984).

Corvallis, OR: Oregon Cooperative Wildlife

Research Unit, Department of Fisheries and

Wildlife, Oregon State University; 1984. 11 p.

Newton, I. Population ecology of raptors.

Vermillion, SD: Buteo Books; 1979. 399 p.

Pitelka, Frank A.; Tomick, P.Q.: Treickel, G.W.

Ecological relations of jaegers and owls as

lemming predators near Barrow, Alaska.

Ecological Monographs. 25: 85-117; 1955.

Sisco, Chuck; Gutiérrez, Ralph J. Winter ecology

of radio-tagged spotted owls on Six Rivers

3

National Forest, Humboldt County, CA. Eureka,

CA: U.S. Department of Agriculture, Forest

Service, Six Rivers National Forest; 1984.

140 p.

Van Horn, Barbara. Density as a misleading

indicator of habitat quality. Journal of

Wildlife Management, 47(4): 893-901; 1983.

c

54
A REVIEW OF CURRENT NORTHERN SPOTTED OWL

(Strix occidentalis caurina) RESEARCH

IN WASHINGTON STATE

Harriet L. Allen and Larry W. Brewer

ABSTRACT : Two spotted owl research efforts are underway in Washington.

One is a study of spotted owl population and ecology and is being conducted and funded by the Washington Department of Game. The other is a

study to evaluate the effectiveness of the Spotted Own Management Area

(SOMA) concept and is funded jointly by the USDA Forest Service and

the Washington Department of Game.

INTRODUCTION

The northern spotted owl was classified as "sensitive" by the state of Washington in 1982; this

classification was changed to "threatened" in

1983. The Department of Game is currently conducting two research projects on the spotted owl.

The first project was initiated in 1982 and was

funded by the Nongame Program of the Department of

Game. It was established to provide facts about

spotted owl ecology that either added to existing

knowledge or clarified unique management questions in Washington. The objectives were to:

1. Determine the population distribution and

status of spotted owls in Washington;

2. Monitor habitat use patterns of adult spotted

owls;

3. Analyze habitats used by adults; and

4. Develop management recommendations for spotted owls in Washington.

A fifth objective, to monitor the dispersal of

juvenile owls, was added during the second year

of the study.

LARRY W. BREWER and HARRIET L. ALLEN are Wildlife Research Biologists with the Washington

Department of Game, Olympia, WA.

The second research project began in 1983 in cooperation with the USDA Forest Service to evaluate

the effectiveness of the Spotted Owl Management

Area (SOMA) concept. The cooperators are the USDA

Forest Service Pacific Northwest Region, including

the Mount Baker-Snoqualmie National Forest, the

Gifford Pinchot National Forest, and the Olympic

National Forest; the Pacific Northwest Forest and

Range Experiment Station Old Growth Research and

Development Project, Olympia, WA; and the Washington Department of Game. Objectives of the

study were to:

1. Determine occupancy rates of SOMAs;

2. Determine how owls are using SOMAs; and

3. Determine how used areas differ from unused

areas.

An overview of the methods and preliminary results of these two projects will be discussed

individually.

SPOTTED OWL ECOLOGY STUDY

Population Levels and Status

We began our work on population evaluation by

conducting a random survey throughout the potential range of the spotted owl in Washington.

This included coniferous forests in both western

Washington and on the eastern slopes of the Cascade Range. 'We divided the study area into

55
20-km (12.5 mi) square cells and then randomly

selected 53 cells in which to run surveys. The

surveys were conducted along 32-km (20-mi) routes

on roads or trails nearest the center of the cells.

Routes were surveyed twice between May and September in both 1982 and 1983. Approximately 40 cooperators from State and Federal agencies and private organizations worked on the spotted owl survey each year.

Along the routes, cooperators stopped every 0.8-km

(0.5 mi) and played a tape of a spotted owl call.

The call was played at specified intervals over a

B-minute period at each listening station. All

owl responses and the direction from which the responses were heard were recorded at each station.

Prior to the spotted owl surveys, each listening

station was evaluated for habitat characteristics.

Data were gathered for a 400-m-radius circle at

each listening station and were recorded in a computer format. The data will be used to compare

habitat among areas where spotted owls responded

and areas where no owls responded.

In spring 1982 we called owls at 1,772 stations

along 48 routes. During this effort we heard 44

spotted owls and 5 barred owls. In spring 1983 we

surveyed 1,289 stations over 35 routes. We heard

33 spotted owls and 16 barred owls. We will attempt to estimate a minimum spotted owl population

level from the census results. Data on barred

owls will be used in a separate evaluation of

barred owl distribution in Washington.

The sites where spotted owls were located during

the surveys will be used as a random sample to

help evaluate the classification status of the

spotted owl in Washington. At each of these sites

we will determine the habitat types, habitat fragmentation, land ownership, and future land use

plans of an area 3.2 km (2 mi) square centered on

the survey listening station.

The information from these analyses will be combined with other pertinent data to make a final

determination of the status of the spotted owl in

Washington. There are no plans to repeat the survey in future years.

Monitoring Habitat Use

The movement and habitat use patterns of 17

spotted owls have been monitored via radio telemetry for varying lengths of time within the Z-year

study period. Seasonal and overall home ranges

for adult male and female owls are being identified. Roosting and foraging concentration areas

within the home ranges are being mapped.

To date, the home range size for the three most

northerly pairs of owls have been evaluated. Two

of these pairs were located near Mount Baker in

the Mount Baker-Snoqualmie National Forest and one

was in the Early Winters Creek drainage, Okanogan

National Forest. The average home range for these

pairs was 2499 ha (6,176 acres). The average home

range for each individual owl was 1648 ha (4,071

acres).

These three preliminary home range estimates are

conservative figures. The owls were monitored

for periods of 120 to 300 days and may represent

as little as 60 percent of the total home range

(Forsman 1984). Preliminary evaluations suggest

that home ranges are larger at the northern end &

of the species' range. We have made preliminary

estimates of the total area of old growth within

the home ranges of these three owl pairs using

1979 classified Landsat satellite imagery (Brew- ,?>

er and Eby 1983). The three home ranges evaluated contain an average of 749 ha (1,850 acres)

of old growth per pair.

Analysis of Habitats Used by Adults

Habitat analyses of use areas will be compared

to habitat analyses of randomly selected plots.

We will also look for disparities in habitats

selected by males vs. females. These habitat

evaluations will be conducted in wet coniferous

forest types in western Washington and in dry

coniferous forest types on the eastern slopes of

the Cascade Range. A major emphasis of this

work will be to compare habitat needs of the

northern spotted owl from the southern limits to

the northern reaches of the species' range.

Throughout the project, spotted owl pellets have

been collected at nesting and roosting sites and

will be used to analyze food habits. Prey species will be identified and results compared

with results from similar studies in California

and Oregon.

4

Monitoring Juvenile Dispersal

Six juvenile spotted owls were trapped and

equipped with raio transmitters in August 1983.

These young birds dispersed from their nest

areas in September and early October and were

monitored throughout the following year by spot

checks from aircraft. Dispersal routes of the

juvenile birds were plotted; distance, direction,

habitat selection, and mortality during dispersal are being evaluated.

The juveniles had a known mortality rate of 67

percent; as of June 1984, four of the six juveniles were dead. We were unable to locate two

of the owls after extensive searches in May and

suspect that the transmitters failed. Preliminary review of the data indicates that dispersal by juvenile spotted owls is random in both

direction and habitat use. We tracked juvenile

owls through a variety of habitats; only a few

of them fit the current concept of adult spotted

owl habitat. Dispersal distances exceeded 48 km

(30 mi) in some cases. In those instances where

two siblings were radio equipped, the birds dispersed from the nest area in generally opposite

-T

directions. The sample size in this study is

small; however, the results should add to the

understanding of juvenile dispersal when combined with the results of similar research con- sducted in Oregon and California.

56
Management Recommendations LITERATURE CITED

The final objective of this research is to provide

recommendations regarding the population status

and management of the northern spotted owl in

-J Washington. The target date for written completion of this research effort is July 1985.

EVALUATION OF THE SPOTTED OWL MANAGEMENT AREA

E (SOMA) CONCEPT

Occupancy Rates of SOMAs

A total of 46 SOMAs were randomly selected for

the monitoring study: 19 in the Mount BakerSnoqualmie National Forest; 17 in the Gifford

Pinchot National Forest; and 10 in the Olympic National Forest. During the first field season

(March - September 1984), we surveyed these 46

SOMAs to determine occupancy. Emphasis of surveying was to locate owls within the SOMAs during the

day rather than at night. SOMAs were surveyed at

night when we were unable to elicit daytime responses. If after 7 surveys throughout the season

we were unable to elicit a response, we considered

the SOMA unoccupied.

We obtained at least one response from a spotted

owl in 43 of the 46 SOMAs. We found no spotted

owls in 3 of the 46 SOMAs. Of the 43 SOMAs with

responses, we got daytime confirmations of a pair

of owls in 12 SOMAs; and daytime confirmations of

a single owl in 11 SOMAs. We got only night-time

I. responses from owls in 20 SOMAs. Of these, seven

were confirmed (according to Forest Service guidelines of three responses more than 72 hours apart)

to contain at least one spotted owl. Thirteen

5

SOMAs had at least one response, but were not verified to contain owls. We obtained barred owl responses in or near eight of the 46 SOMAs. We

found no reproduction in any of the 46 SOMAs surveyed.

Owl Use of SOMAs

We monitored five owls during the first field

season. Preliminary results indicated an average

summer range area of 968 ha (2,391 acres) (range:

257 ha (634 acres) to 1765 ha (4,362 acres)).

From 0 to 85 percent (x = 35.5 percent) of the

locations were within the SOMAs; summer ranges

overlapped the SOMAs by 0 to 44 percent (x = 20.5

percent). Winter tracking is continuing on these

SOMAs during 1984-85. We will monitor nine pairs

of birds (three SOMAs on each forest) during 1985.

Comparison of Used vs. Unused Areas

%

Habitat analyses of used vs. unused areas will begin during the 1985 field season. Vegetation

analysis that incorporates concentric circular

plots (Spies 1983) randomly located in used and

unused habitat, will be conducted in each of the

3 home ranges of monitored owls. This effort will

concentrate on those portions of home ranges that

fall within the SOMAs.

Brewer, Larry; Eby, James. A Washington state

LANDSAT ground cover classification. Washing- -

ton Department of Game Pitman-Robertson Report, Project W-92-R. Olympia. 1982. 121 p.

Forsman, Eric. Distribution and biology of the

spotted owl in Oregon. Wildl. Monogr. No. 87.

1984. 64 p.

Spies, Thomas. Draft study plan: Characterization of old-growth douglas-fir forests of

western Oregon and Washington. USDA Forest

Service Unpublished Report, Oregon State University, Corvallis. 1983. 37 p.

57
OLD-GROWTH FOREST RETENTION FOR SPOTTED OWLS--HOW MUCH DO THEY NEED?

Eric D. Forsman and E. Charles Meslow

ABSTRACT: Pairs of adult owls in Oregon were studied by radiotelemetry

to determine their home ranges and the acreages of old-growth forest in

the home ranges. Six pairs were studied for 3 to 13 months. The pairs

used 1,008-3,786 acres of old growth, averaging 2,264 acres per pair.

The 1,008-acre figure provided the basis for management recommendations.

INTRODUCTION

In 1980 the Oregon-Washington Interagency

Wildlife Committee recommended that the amount

of old-growth forest retained for individual

pairs of spotted owls be increased from 300 to

1,000 acres (121-405 ha) (Oregon-Washington

Interagency Wildlife Committee 1980). This

recommendation was based on data gathered during

radio-tracking studies of spotted owls in Oregon

between 1975 and 1980 (Forsman 1980, 1981;

Forsman and others 1984). During these studies,

14 adult spotted owls were fitted with radio

transmitters and tracked for periods ranging

from 3 to 13 months. In 6 cases, we were able

to track both members of a resident pair of owls.

At the end of the tracking period, the total

home range of each pair of owls was determined,

and the amount of old growth within each home

range was determined from orthophotos. The

minimum amount of old growth within the home

ranges of the 6 pairs studied was 1,008 acres

(405 ha) as reported by Forsman (1981) and

Forsman and others (1984).

Subsequent to the 1980 revision of the spotted

owl management plan, we received a number of -

requests to display all the data relating to the

amount of old growth within the home ranges

occupied by the pairs of owls that we studied

(only the minimum acreage figure was cited in

our initial reports). The purpose of this

report, therefore, is to display the complete

set of data concerning the amount of old growth

within the home ranges of the 6 pairs of owls.

ERIC D. FORSMAN is a wildlife biologist residing

at 580 S.E. Corliss Ave., Corvallis, OR. E.

CHARLES MESLOW is leader, Cooperative Wildlife

Research Unit, Oregon State University,

Corvallis, OR.

OLD GROWTH PER PAIR 2:

The area of old-growth forest in the home ranges

of the radio-tagged pairs is shown in table 1.

As described in Forsman (1980, 1981) and Forsman

and others (1984), data from the lA and 2C pairs %

58
(table 1) should be viewed with caution because

there was some question about the stability of

those pairs. The other 4 pairs, however,

appeared to be comprised of well-established

individuals.

Table l--Amount of old-growth forest within home

range areas utilized by 6 pairs of radio-tagged

spotted owls in northwestern Oregon

Pair no. Home range size 1/ Old-growth area

IA 10,146 3,786

2A 3,945 2,092

5A 3,969 2,248

1c 10,440 2,262

2c 8,343 2,191

3c 2,840 1,008

Mean 6,614 2,264

Std. Dev. 3,419.5 886.5

1/ Areas given indicate the total home range area

used by each pair of owls. Home ranges utilized

by individual owls were described in Forsman and

others (1984).

The old-growth acreages used by the pairs of

spotted owls in our studies do not appear unusual.

Recent studies in California and Washington

indicate that pairs of spotted owls use extensive

areas of old-growth and mature forest in those

areas as well (Sisco 1984; Solis 1983; Harriet

Allen, pers. comm. 1984 1/).

A/Washington State Game Department study in

progress. Data on file with Harriet Allen,

Washington State Game Department, Olympia, WA.

Because of economic concerns, the approach to

spotted owl management in Oregon has been to manage

for the minimum number of pairs necessary to

sustain a genetically viable population and to

provide each pair with a minimum amount of

old-growth habitat. This approach involves a high

degree of risk because it is unlikely that any

species will prosper if it is reduced to minimum

numbers and, at the same time, provided with a

minimum amount of suitable habitat. To mitigate

the effects of minima1 numbers and minimal areas of

habitat, managers should attempt to ensure that

old-growth habitat that is retained for spotted

owls is of the highest quality available.

LITERATURE CITED

Forsman, Eric D. Habitat utilization by spotted

owls in the west-central Cascades of Oregon.

Corvallis, OR: Oregon State University; 1980.

Ph.D. dissertation. 95 p.

Forsman, Eric D. Habitat utilization by spotted

owls on the Eugene District of the Bureau of Land

Management. Portland, OR: Bureau of Land

Management; 1981. 63 p.

Forsman, Eric D.; Meslow, E. Charles; Wight,

Howard M. Biology and management of the spotted

owl in Oregon. Wildlife Monograph No. 87; 1984.

64 p.

Oregon-Washington Interagency Wildlife Committee.

Oregon spotted owl management plan. Portland, OR:

Oregon Department of Fish and Wildlife; 1980. 2 p.

Sisco, C.; Gutiérrez, R. J. Winter ecology of radiotagged spotted owls on Six Rivers National

Forest, Humboldt Co., CA. Eureka, CA: U.S.

Department of Agriculture, Forest Service, Six

Rivers National Forest; 1984. 139 p.

Solis, David M., Jr. Summer habitat ecology of

spotted owls in northwestern California. Arcata,

CA: Humboldt State University; 1983. M.S. thesis.

168 p.

59
JUVFNILE SPOTTED OWL DISPERSAL IN NORTHWESTERN CALIFORNIA: PRELIMINARY RESULTS 

R. J. Gutigrrez, Alan B. Franklin, William Lahaye, 

Vicky J. Meretsky, and J. Patrick Ward 

ABSTRACT: Dispersal ecology of juvenile spotted owls was studied in 

northwestern California during 1982 and 1983. Breeding spotted owls were 

not found in northwestern California in 1982. In 1983, we radio-marked 

13 juvenile owls. Eleven owlets survived to disperse between 2 September 

and 23 October 1983. The total dispersal distances for these owlets 

ranged from 30 km to 156 km (x = 78 km). The final dispersal distance 

measured as a straight Line from the nest to the location of juvenile 

mortality or transmitter failure ranged from 20 km to 98 km (x = 45 km). 

An analysis of dispersal directions using circular statistics showed 

that, as,a group, juveniles dispersed in a southerly direction (154O). 

We Lost radio contact with four of the owls, while the remaining seven 

died. Causes of mortality included a presumed accident (L), animal 

predation (11, starvation (3), undetermined (4). The management 

implications for these preliminary results are discussed. 

INTRODUCTION 

The northern spotted owl (Strix occidentalis 

caurina) is closely associated with old-growth 

Douglas-fir (Pseudotsuga menziesii (Mirb.) 

France) forests from southwestern British 

Columbia through northwestern California 

R. J. GUTIERREZ is an associate professor of 

wildlife management and chairman of the Dept. of 

Wildlife at Humboldt State University, Arcata, 

CA. ALAN FRANKLIN, WILLIAM LAHAYE and VICKY 

MERETSRY are graduate students in wildlife 

management and J. PATRICK WARD is an undergraduate student in wildlife management at 

Humboldt State University, Arcata, CA. 

(Forsman 1980, Solis 1983). The rapid harvest of 

these forests in the Pacific Northwest has led to 

a population decline of the northern spotted owl 

(Forsman and others 1984, U. S. Fish and Wildlife 

Service 1982). In response to this decline, the 

USDA Forest Service established Spotted Owl 

Teritories (SOTS) that are developed from habitat 

and home range studies conducted by Forsman (1980) 

and Solis (1983). Although data exist for establishing guidelines for SOT habitat quality and 

quantity, no data exist for determining an 

appropriate distribution of SOTS. 

The maintenance of effective population size 

(Barrowclough and Coats 1985) and the correct 

spatial organization of SOTS cannot be 

adequately predicted without an understanding of 

dispersal. The importance of animal dispersal 

to demography, genetics, and.social behavior has 

60 

i 
been documented for a wide variety of taxa 

(Greenwood 1980, Lidicker 1962, Lidicker and 

Caldwell 1982, Southwood 1962). For this paper, 

dispersal is defined as nonmigratory movement by 

an individual beginning with its departure from 

the natal area and ending with the establishment 

of a breeding territory. In this paper, we 

present some initial observations on the 

dispersal of juvenile spotted owls in northern 

California and discuss the implications for the 

management of this species. 

MATERIALS AND METBODS 

The dispersal ecology of northern spotted owls 

was studied in northwestern California from 1982 

to 1983. Because of a region-wide breeding 

failure of spotted owls in 1982, data on 

dispersing juveniles were not collected until 

1983. 

Our study area encompasses portions of the Six 

Rivers, Rlamath, and Shasta-Trinity National 

Forests in northwestern California. The area is 

dominated by rugged topography and numerous river 

and stream systems. Elevations of the study area 

range from 300 m to 1500 m. The climate is 

typically wet and cool in winter, with snow at 

higher elevations; summers are hot and dry. 

Average yearly precipitation for the study area 

is approximately 142 cm. 

The study is limited to Douglas-fir forests 

because spotted owls appear to be more abundant 

in this habitat (Porsman and others 1984); this 

vegetation type is also the most extensive and 

valuable of the old-growth forests in northwestern California. The vegetation seres are 

more completely described by Sawyer and others 

(1977) and Solis (1983). 

Nests and juveniles were located in the manner 

described by Forsman (1984). Juveniles were 

captured using a dip net constructed of mist 

netting. Each captured juvenile was banded with 

a U. S. Fish and Wildlife Service aluminum leg 

band and outfitted with a radio transmitter 

attached to a backpack of 5-mm teflon ribbon 

(Solis 1983). The birds were released within 18 

min and observed to determine behavioral 

reactions. 

Radio-marked owls were monitored using the 

methods outlined by Solis (1983). Owl locations 

were plotted on U. S. Geological Survey topographic maps (1:24000) using a minimum of three 

compass bearings from monitoring points with the 

bearing describing the peak radio signal 

(Springer 1979). 

Juvenile owls were initially monitored at least 

once a week to determine location or mortality 

prior to dispersal. We tracked dispersing 

juveniles from the ground as closely as terrain 

and weather conditions permitted. Telemetryequipped aircraft were used to relocate owlets 

lost during ground tracking and for monitoring 

owlets in inaccessible areas. 

Dispersal directions and direction-distance 

vectors were analyzed using circular statistics 

(Batschelet 1981). 

Table l--Summary of dispersal distances and fates of 13 juvenile spotted owls, Strix occidentalis 

caurina, from northwestern California, 1983 

Owl Sex&/ 

Total Final 

Date - Date Date Distance Distance Fate 

Sighted Banded Died km' (mi) -km (mi) 

Tonto M 30 Jun 26 Jul 22 Sep 0 ( 0) 0 ( 0) Dead 

Fang U 1 Jul 7 Jul 9 Ott 32 (19) 26 (16) Dead 

Titus U 30 Jun 6 Jul 25 Nov 128 (77) 99 (62) Dead 

Bertha U 18 Aug 23 Aug 2 Feb 45 (27) 22 (13) Unstabl&/ 

Merlyn U 11 Aug 19 Aug 20 Mar 163 (98) 67 (41) Dead 

Ranger M 22 Jun 6 Jul 29 Mar 63 (38) 44 (27) Dead 

Cheech U 23 Jun 11 Jul 17 Jan 77 (46) 42 (26) Stable?/ 

Chong U 23 Jun 13 Jul 21 Nov 73 (44) 56 (35) Dead 

Jake U 24 Jun 20 Jul 20 Dee 138 (86) 42 (26) Dead 

Elmo U 24 Jun 14 Jul 25 Nov 60 (36) 53 (32) Dead 

Sugarbaby U 17 Jun 12 Jul 2 Sep 0 ( 0) 0 ( 0) Dead 

&rpY U 17 Jun 8 Jul 3 Jan 45 (27) 23 (14) Unstable 

Shrew U 6 Jul 21 Jul 17 Jan 70 (42) 35 (22) Unstable 

11 

a 

Sex M = male; U = unknown. 

f/ 

Unstable = dispersal in progress when transmitter failed. 

Stable = settled in a restricted area before transmitter failed. 

61 
RESULTS AND DISCUSSION consistently the juvenile moved in a single

direction. Observations from all of the birds

were combined to calculate a group direction or

vector (0). The group direction for all

juveniles was 0 = 154O

 with r = 0.35. The low

r value indicated that directions taken between -2

dispersal movements were variable. Rayleigh and

Rao's spacing tests (Batschelet 1981) showed that

five birds were heading in a particular compass

direction. The remaining birds' movements were. SI

not shown to be significantly different from a

random distribution. The group direction (0),

however, was significantly different from a

random distribution according to both the

Rayleigh and Rao's spacing tests. As a group,

the juveniles therefore appeared to be moving in

a southerly direction (0 = 1540; fig. 1).

For each owl, a bivariate vector was plotted

using distance and direction from the nest to

the owl's final known location (fig. 2). A mean

vector (M) of 188o and 34 km (21.1 mi) was

calculated for the sample of vectors. Again, as

a group, the juveniles appeared to be moving in

a southerly direction.

Hotelling's confidence ellipse (Batschelet 1981)

was calculated to determine the area covering

Dispersal Patterns

All marked, surviving juveniles dispersed

between 2 September and 23 October 1983 (table

1). Sixty-four percent (7 juveniles) dispersed

within a 9-day period from 19 September to 27

September. The degree of parental care at the

time of dispersal was not known, but after a

bird left its natal area, it did not return.

Dispersal distance and direction.-The total

dispersal distance, which is the sum of dispersal

movements for an individual owl, ranged from 30

km to 156.km (19 mi to 97.6 mi) with a mean of

78 km (48.4 mi) (table 1). The final distance

measured as a straight line from the nest to the

location of the juvenile mortality or transmitter

failure ranged from 20 km to 98 km (12 mi to

61.5 mi) with a mean of 45 km (28.3 mi).

The directions in which dispersing owlets

traveled were averaged and represented as vectors

of dispersal (fig. 1). The r values associated

with each vector represent the measure of concentration of the individual directions taken by

each bird. The higher the r value, the more

Figure 1. --Direction vectors for 11 dispersing

juvenile spotted owls, Strix occidentalis

caurina, from northwestern California, 1983.

0 = an overall group direction; r = the measure

of concentration of 0 (Batschelet 1981).

DISTANCE &

DIRECTION

M =33.8 km 8 18EP

Vector Scale 10

Figure 2. --Bivariate vectors using distance and

direction from nest to final location for 11

;r,

dispersing juvenile spotted owls, Strix

occidentalis caurina, from northwestern

California, 1983. M = the sample mean; the

outer ellipse is one standard deviation around ,&

the mean; the inner, a 95% Hotelling's

confidence ellipse (Batschelet 1981).

62
the true population center of dispersing juvenile

owls with 90 percent probability. In other

words, with the starting point at the nest

(origin) there is a 90 percent probability that

the population mean of final dispersal locations

i

of juvenile spotted owls would be included within this ellipse.

When the circumstances allowed us to closely

follow individuals that were dispersing, we found

t that these birds typically moved rapidly and

unidirectionally. The average rate of movement

for all birds was 8 km/day (5.03 mi/day), with a

range of 1.6-17 km/day (l-10.9 mi/day).

After an initial rapid movement from the natal

area, most (n = 8) of the owlets attempted to

settle. Three of these owlets, which were

monitored closely, had home ranges of 362 to 461

ha (882 to 1125 acres>. After settling, six of

the owlets died or their transmitters failed.

Two continued to disperse after remaining four to

seven weeks in their respective areas. One owl

roosted and foraged for several days in the same

area on three separate occasions and made two

round trips of 6 and 50 km (4 and 31 mi). The

owlet died 19 km (12 mi) from the area during its

third departure.

Effect of barriers and habitat on dispersal.--

Geographic and topographic barriers did not

noticeably affect direction of dispersal.

Owlets frequently crossed major ridges and rivers

during dispersal; for example, one bird crossed

-7 three large rivers (75-100 m width) and two major

ridges (1200-1500 m elevation) during its

dispersal.

Juvenile owls readily crossed habitats in north-

.a western California that would be classified as

unsuitable for spotted owls (Gutiérrez and others

1984, Solis 1983). Although owlets frequently

entered these areas, they often died there as

well. Unsuitable habitats (for example, clearcuts and oak woodlands) may be effective barriers

to dispersal, but this does not seem to deter the

birds from entering them.

 Juvenile Mortality

All of our marked juveniles (n = 7) that survived

to disperse, and whose transmitter batteries did

not fail, died during dispersal. Causes of

mortality included predation (11, starvation (31,

and undetermined (3). Four transmitter batteries

failed before they could be replaced. TWO

juveniles died before dispersing, one from an

apparent accident (punctured eye) and the other

from unknown causes. Because none of the

juveniles survived to established breeding

territories, the distances recorded in our study

-; cannot be considered net effective dispersal

distances.

It has long been known that dispersing animals

3‘ incur high mortality rates (Howard 1960, Lidicker

and Caldwell 1982). Juvenile tawny owls (Strix

aluco) exhibited average first-year mortality

rates between 47 and 66 percent under normal

conditions (that is, without decreasing habitat

limitations) (Southern 1970), Barrowclough and

Coats (1985) calculated an expected first-year

Surivorship for spotted owls to be 19 percent.

A population of owls could, clearly, not maintain

itself with a mortality of 100 percent such as we

observed. Our sample size is small enough that

one might expect the entire group to die by

chance alone (Barrowclough and Coats 1985). An

larger sample size may be needed to detect the

19 percent survivorship. Despite such a high

first-year mortality rate, spotted owls may be

sufficiently long-lived that they could replace

themselves within their reproductive lives.

MANAGEMENT IMPLICATIONS

There are three important implications of our

preliminary findings. First, our study

demonstrates that juvenile spotted owls move

considerably farther than previously observed

(Forsman and others 1984). Yet, our data are

consistent with those reported in this symposium

by Miller and Meslow (1985). Owlets are

aggressive dispersers and travel rapidly over

topographic barriers and into or through unsuitable habitat. Inter-SOT distances should not,

however, be increased to reflect these long

dispersal distances. Because owlets move

directionally, the probability of a juvenile owl

encountering a SOT would decrease as the

inter-SOT distance increases.

Second, we do not know how long-term population

viability will be affected if adequate dispersal

sinks (as defined by Lidicker 1962, habitats

where nonbreeding owls can persist until breeding

habitat becomes available) are not available for

juvenile owls. Because spotted owls are probably

long-lived, SOTS may be occupied for a long time.

A SOT management scheme without consideration for

dispersal sinks must depend almost entirely on

the current year's productivity to fill available

SOTS. Thus, the most productive habitat or pairs

of owls should be maintained to ensure adequate

productivity. We believe that establishing SOTS

with pairs of owls that show sporadic or no

productivity are inadequate for maintaining a

viable population. The reasons for this are:

(1) adults have a variable reproductive pattern

(Gutiérrez 1985, Gutiérrez and others 1984); (2)

juveniles have a low survivorship (Barrowclough

and Coats 1985, Forsman and others 1984, Miller

and Meslow 1985); and (3) there is continuing

habitat deterioration.

Third, the influence of dispersal on the

survivorship of juvenile spotted owls and

effective population size is presented by

Barrowclough and Coats (1985). If the high

juvenile mortality we observed is, in part, due

to deteriorating habitat (that is, increased

patchiness and loss of old growth), then we

might predict (1) lower survivorship of juveniles

as this deterioration continues and (2) an

increase in dispersal distance required to reach

suitable habitat. In turn, effective population

size is strongly influenced by these dispersal

63
distances (Barrowclough and Coats 1985).

Ultimately, the long-term viability of spotted

owls in the Pacific Northwest will be a function

of effective population size and colonization of

habitat patches that are partially dependent on

dispersal ecology (Barrowclough and Coats 1985,

Frankel and Soulé 1981, Gutiérrez and others

1984, Schaffer 1985). SOTS should be established

with appropriate habitat characteristics, as

described by Forsman and others (1984) for mesic

Oregon, by Solis (1983) and Gutiérrez and others

(1984) in northwestern California, and by Layman

(1985) in the Sierra Nevada. SOTS should not be

designated solely on their value (or lack

thereof) as a timber resource. Many of the most

productive habitats appear to be in valuable

timber stands. If adequate protection is to be

provided for spotted owls, SOTS must be placed

in these stands, commercial values notwithstanding. Above all, spotted owl management

plans must be allowed some flexibility (Gutiérrez

and others 1984) to accommodate new and relevant

findings on spotted owl dispersal.

ACKNOWLEDGMENTS

We would like to thank Don Kudma, Jeff Mattison,

Rolando Mendez, Jan Stevenson, David Solis,

Marilyn Stoll, Ed Toth, and Becky Oz of the Six

Rivers National Forest; Edie Asrow, Don Bright,

Alan Scott, and Lou Waltering of the Klamath

National Forest; Terry Brumley, Lynn Shipley,

Kim Stokely and Paul Weeden of the ShastaTrinity National Forest; Jim Decker of the Bureau

of Land Management; and Gordon Gould of the

California Department of Fish and Game. All of

these people were extremely helpful with our

field efforts. We also thank Len Ruggiero for

his support in funding. Andrew Carey, Hal

Salwasser, Carl Marti and Jared Verner kindly

reviewed the manuscript. Jay Brown made the

illustrations and Bruce Garlinger provided

air service.

Funding for this project was provided by the OldGrowth Forest Wildlife Habitat Program, USDA

Forest Service, Forestry Sciences Laboratory,

Olympia, Washington. This is contribution 84-2

of the College of Natural Resources, Humboldt

State University, Arcata, California.

LITERATURE CITED

Batschelet, Edward. Circular statistics in

biology. New York, NY: Academic Press; 1981.

371 p.

Barrowclough, George F.; Coats, Sadie. The

demography and population genetics of owls,

with special reference to the conservation of

the spotted owl (Strix occidentalis). In:

Gutiérrez, Ralph J.; Carey, Andrew B., tech.

eds. Ecology and management of the spotted owl

in the Pacific Northwest. Gen. Tech. Rep.

PNW-185. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest

Forest and Range Experiment Station; 1985:

74-85.

Forsman, Eric D. Habitat utilization by spotted

owls in the west-central Cascades of Oregon.

Corvallis, OR: Oregon State University; 1980.

Ph.D. dissertation. 95 p.

Forsman, Eric D.; Meslow, E. Charles; Wight,

Howard M. Biology and management of the

spotted owl in Oregon. Wildlife Monograph No.

87; 1984. 64 p.

Frankel, 0. H.; Soulé, Michael E. Conservation

and evolution. Cambridge, England: Cambridge

University Press; 1981. 327 p.

Greenwood, P. J. Mating systems, philopatry and

dispersal in birds and mammals. Animal

Behavior. 28: 1140-1162; 1980.

Gutiérrez, R. J. An overview of recent research

on the spotted owl. In: Gutiérrez, Ralph J.;

Carey, Andrew B., tech. eds. Ecology and management of the spotted owl in the Pacific

Northwest. Gen. Tech. Rep. PNW-185. Portland,

OR: U.S. Department of Agriculture, Forest

Service, Pacific Northwest Forest and Range

Experiment Station; 1985: 39-49.

Gutiérrez, R. J.; Solis, David M.; Sisco,

Charles. Habitat ecology of the spotted owl in

northwestern California. In: Proceedings of

the convention of the Society of American

Foresters; 1983 October 16-20; Portland, OR:

American Society of Foresters; 1984: 368-373.

Howard, W. E. Innate and environmental dispersal - &

of individual vertebrates. American Midland

Naturalist. 63: 152-161; 1960.

Layman, Stephen A. General habitats and movements -e

of spotted owls in the Sierra Nevada. In:

Gutiérrez, Ralph J.; Carey, Andrew B., tech.

eds. Ecology and management of the spotted owls

in the Pacific Northwest. Gen. Tech. Rep.

PNW-185. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest

Forest and Range Experiment Station; 1985:66-68.

Lidicker, W. Z., Jr. Emigration as a possible

mechanism permitting the regulation of

population density below carrying capacity.

American Naturalist. 96: 29-33; 1962.

Lidicker, W. Z., Jr.; Caldwell, R. L., eds.

Dispersal and migration. Benchmark papers in

Ecology 11. Stroudsberg, PA: Hutchinson

Publishing Co.; 1982. 309 p.

Miller, Gary S.; Meslow, E. Charles. Dispersal

data for juvenile spotted owls: the problem of

small sample size. In: Gutiérrez, Ralph J.;

Carey, Andrew B., tech. eds. Ecology and

management of the spotted owl in the Pacific

Northwest. Gen. Tech. Rep. PNW-185. Portland, 5-

OR: U.S. Department of Agriculture, Forest

Service, Pacific Northwest Forest and Range

Experiment Station; 1985: 69-73.

64
Sawyer, John 0.; Thornburgh, D. A.; Griffen,

J. R. Mixed evergreen forest. In: Barbour, M.;

Major, J., eds. Terrestrial vegetation of

California. New York, NY: John Wiley and Sons,

Inc.; 1977: 359-415.

2

Schaffer, Mark L. The metapopulation and species

conservation: the special case of the northern

spotted owl. In: Gutiérrez, Ralph J.; Carey,

0

Andrew B., tech. eds. Ecology and management of

the spotted owl in the Pacific Northwest. Gen.

Tech. Rep. PNW-185. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific

Northwest Forest and Range Experiment Station;

1985: 86-99.

Solis, David M. Summer habitat ecology of spotted

owls in northwestern California. Arcata, CA:

Humboldt State University; 1983. 168 p. M.S.

thesis.

Southern, H. N. The natural control of a population of tawny owls (Strix aluco). Journal of

zoology. 162: 197-285: 1970.

Southwood, T. R. E. Migration of terrestrial

arthropods in relation to habitat. Biological

Review 37: 171-175; 1962.

Springer, J. T. Some sources of bias and sampling

error in radio triangulation. Journal of Wildlife Management. 43: 926-935; 1979.

U.S. Fish and Wildlife Service. The northern

spotted owl: a status review. Portland, OR:

U.S. Department of Interior, Fish and Wildlife

Service; 1982. 29 p.

65
GENERAL HABITATS AND MOVEMENTS OF SPOTTED OWLS IN THE SIERRA NEVADA

Stephen A. Layman

ABSTRACT: This paper reports a summary of a 3-year research project on

the California spotted owl in the central Sierra Nevada of California. /

Owls with radio transmitters were tracked and vegetation parameters were

measured on summer, autumn, and winter roosting plots and on randomly

located plots within the owl's home range. The discovery of downslope

migrational movements and establishment of winter home ranges in the foothill

woodland was a significant finding which may indicate a subspecies difference

and which raises previously unthought of management problems. The

ramifications of these new management issues are discussed.

.,

4

INTRODUCTION

A great deal of research has been undertaken on

the northern spotted owl (Strix occidentalis

caurina). Forsman and others (1484) completed

eight seasons of field work in west-central

Oregon, including two years of radio telemetry on

two study sites. Gutiérrez and associates at

Humboldt State University, Arcata, California,

have conducted a 5-year research effort to examine

winter and summer habitat use and juvenile

dispersal of spotted owls in northwestern

California. The California subspecies, Strix

occidentalis occidentalis, which ranges from

northeastern Tehama Countv south through the

 Sierra Nevada and the high mountain ranges of

southern California, and in the Coast Range from

southern California north to Monterey County, has

received little attention from researchers. The

only published information consists of work on

 thermoregulation (Barrows 1981) and on food

habits (Barrows 1480, Marshall 1942).

The current study, from 1982 to 1984, was'

designed to fill in gaps in the knowledge of *

the natural history, life history,, habitat

selection, and juvenile dispersal in the

Sierra Nevada population of the California

spotted owl, and to determine if there were

differences between the northern and California

subspecies. Presented here is an outline of

the general accomplishments and progress of

the study.

STUDY AREA

The study was conducted primarily between the

middle. and south forks of the American River in

El Dorado and Placer Counties, California.

Elevation was 300-2000 m and the study area

encompassed 500 km2. University of California

at Berkeley Blodgett Forest Research Station,

near Georgetown, California, was the base of

operations for the study. Habitat types in the

study area included mixed conifer forest, red

fir forest , yellow pine forest, pine-oak

woodland, and oak Savannah. r

STEPHEN A. LAYMON is a research assistant,

Department of Forestry and Resource Management,

the University of California, Berkeley,

Berkeley, Calif.

66
METHODS

Radio Telemetry

A total of 13 adults and 12 juveniles were

equipped with radio transmitters during the

3-year study. Adult foraging sites and winter

roosting sites were located using triangulation

methods from known locations. Summer and autumn

roosting sites for both adults and juveniles were

located visually with the aid of radio telemetry.

Vegetation Sampling

Vegetation was sampled on 15-m-radius plots

centered on roosting, foraging, and random trees.

All trees greater than 10 cm diameter at breast

height (d.b.h.), total height, height of first

foliage, and average radius of foliage.

Additionally, tree species, shape, and condition

were recorded. Canopy closure was estimated

using an inverted monocular with plastic

prism grid. Shrubs and trees smaller than 10 cm

d.b.h. were sampled with a 0.5-m-wide belt transect. Dead and down material was sampled with

line intercept methods (Brown 1974). Slope and

aspect were also measured. Sampling was done at

randomly selected roost and foraging sites and at

sites determined by coordinates randomly selected

from a grid placed over a map of each pair's home

range.

RESULTS

Vegetation Sampling

Vegetation was measured at 10 summer (June-August)

roosting sites and 10 summer foraging sites for

each of 12 paired adults. Roosting sites and

foraging sites were characterized for nine adults

during the autumn (September-October). Twenty

random points were surveyed within the home range

of each pair. Vegetation was also sampled at

15 roosting sites and at 15 random points in

winter-use areas of four birds. Sampling on a

total of 50 vegetation plots was also completed

at juvenile roosting sites. Analysis of vegetation

data is not yet complete. A cursory look at the

data shows little similarity along summer roosting

sites, foraging sites, and randomly selected sites,

and between winter roosting and winter randomly

selected sites. Great similarity is found between

autumn roosting and autumn foraging sites.

Food Habits

Approximately 800 pellets of regurgitated,

undigested portions of prey items have been

collected and analyzed. A much higher diversity

of prey items by species has been found in this

study than in others. The 1982 data, based on

eight pairs of owls and 522 food items, show

an almost equal division of biomass eaten:

northern flying squirrels (Glaucomys sabrinus),

30 percent; dusky-footed woodrats (Neotoma

fucipes), 22 percent; western gray squirrels

(Sciurus griseus), 22 percent; and birds, 16

percent. The 1983 data show a similar pattern.

Reproductive Success

Reproductive success has been quite low for the

three years of the study. During 1482 and 1983

only 1 of 14 pairs produced young (7 percent).

In 1984, 3 of 12 pairs produced young in the

Eldorado National Forest study site and 3 of 10

pairs produced young in the Stanislaus National

Forest -- a success rate of 27 percent.

Juvenile Mortality

I observed 11 juveniles during the post fledgingpredispersal period. Seven of the the juveniles

died; three dispersed. I am currently monitoring

one juvenile that has not yet dispersed. Of the

seven deaths, four were attributed to predation

and three to starvation.

Migratory Movements

I monitored four adult owls by radio telemetry

during autumn 1983. In late October the four

owls began moving downslope to the southwest.

One bird was tracked daily during this time.

It moved 3-6 km each night, traversing the 29 km

between breeding and wintering sites in seven

nights. This bird dropped in elevation from

1600 to 930 m. The other three owls moved from

19 to 32 km and dropped in elevation an average

of 700 m. All four owls circulated through areas

of 300-2000 ha, which appeared to be a winter

home range. The birds remained in the wintering

areas until at least late February. All four

birds returned by mid-April to their nest sites

used the previous year.

The areas occupied during the winter were

pine-oak woodlands in contrast to the mixed

conifer forest used during the summer. All

wintering areas were below the level of

persistent winter snow, which is approximately

1300 m in this part of the Sierra Nevada.

DISCUSSION

All findings from the study indicate that

natural history patterns of the California

spotted owl in the central Sierra Nevada differ

significantly from those of the northern spotted

owl in northwestern California and Oregon. The

migratory movement is of special interest. It

indicates a significant behavioral difference

that may be linked to subspeciation.

Migration also creates significant management

complications because it takes owls from summer

home ranges primarily in USDA Forest Service

jurisdication to winter home ranges which are

primarily in areas that are privately owned.

In addition, the winter home ranges are in the

elevational and geographical area that is growing

faster in human population than any other area

in California.

The migratory movement underscores the importance

of multiple studies on a species in different

geographical areas to determine the range of a

67
species' behavior. It also points out the

dangers of imposing a management plan for a

species in a geographical region other than the

one where the ecological data, on which the plan

was based, was gathered. On the west slope of

the Sierra Nevada, USDA Forest Service management

plans designed to maintain breeding populations

of spotted owls may not be adequate if the

majority of the owls are dependent on winter

habitats in the foothill zone, which is growing

fast in human population. A much more

complicated management effort involving USDA

Forest Service, United States Department of the

Interior Bureau of Land Management, California

Department of Fish and Game, California Department

of Forestry, county Boards of Supervisors, and the

California State Legislature may be necessary to

provide year-round habitat for the spotted owls.

Factors such as fuelwood harvest, clearing

woodland areas for cattle grazing, and subdivision

of land for housing are all impacts on the

foothill zone; these impacts will certainly become

more serious in the future. This study has

pointed out a previously unknown problem that

makes the management of spotted owls in the Sierra

Nevada a much more difficult task than previously

thought. Whether management agencies can meet

this challenge will be seen in the years ahead.

ACKNOWLEDGMENTS

This study was funded by USDA Forest Service,

Pacific Southwest Forest and Range Experiment

Station, Berkeley, California, under a

cooperative agreement with the University of

California at Berkeley, Department of Forestry

and Resource Management, and a contract with

California Department of Fish and Game. Special

thanks must go to the 14 volunteers and

near-volunteers without whom this study would not

have been possible. Special mention goes to

Janice A. Reid who contributed to all aspects of

the project and to Regina1d H. Barrett who has

provided equipment, encouragement, and counsel

throughout the project.

LITERATURE CITED

Barrows, Cameron W. Feeding ecology of the spotted

owl in California..Raptor Research. 14:73-77;

1980.

&

Barrows, Cameron W. Roost selection by spotted

owls: an adaptation to heat stress. Condor.

83:302-309; 1981.

Brown, J. K. Handbook for inventorying downed

woody material. Gen. Tech. Rep. INT-16.

Ogden, UT: U.S. Department of Agriculture,

Forest Service, Intermountain Forest and

Range Experiment Station; 1974. 24 p.

-3

Forsman, Eric D.; Meslow, E. Charles; Wight,

Howard M. Distribution and biology of the

spotted owl in Oregon. Wildlife Monograph.

87:1-67; 1984.

Marshall, Joe T., Jr. Food and habitat of the

spotted owl. Condor. 44:66-67; 1942.

68
DISPERSAL DATA FOR JUVENILE SPOTTED OWLS: THE PROBLEM OF SMALL SAMPLE SIZE

Gary S. Miller and E. Charles Meslow

ABSTRACT: Collection and interpretation of dispersal data for juvenile

northern spotted owls (Strix occidentalis caurina), based on preliminary

information from Oregon, are discussed. Criteria for determining when

dispersal ends and methods of measuring dispersal distances are examined.

Small sample sizes, caused by unpredictable reproduction and high juvenile

mortality, account for much of the problem in studying juvenile dispersal.

INTRODUCTION

Dispersal, on some scale, is an attribute of most

animals. Dispersal and its patterns are basic to

a species' life history strategy and affect nearly

all aspects of a species' ecology and behavior

(Horn 1983). Dispersal is the mechanism that

brings about colonization of unoccupied areas and

gene flow between populations. Dispersal has also

been proposed as an important factor in population

regulation (Lidicker 1962). While the importance

of dispersal has been recognized for some time,

the ability to obtain detailed dispersal information has been limited for most species.

Dispersal has been defined differently by various

investigators. Howard (1960) defines it as "the

movement the animal makes from its point of origin

to the place where it reproduces or would have

reproduced if it had survived and found a mate."

Others simply define dispersal as the movement of

an individual from its natal area to a new area or

succession of areas (Greenwood 1980, Shields

1982). These later authors add, however, that

successful dispersal requires the individual to

reproduce following dispersal movements. We will

distinguish between dispersal and successful

dispersal.

GARY S. MILLER is a research assistant with the

Cooperative Wildlife Research Unit, Oregon State

University, Corvallis. E. CHARLES MESLOW is

leader of the Cooperative Wildlife Research Unit,

Oregon State University, Corvallis.

Information on avian dispersal has historically

come from band returns or sightings of marked

individuals (Erickson 1938, Gibb 1954, Johnston

1956, Kluijver 1951). Dispersal information, for

owls in particular, has been gained from various

banding studies (Houston 1978, Stuart 1952, Van

Camp and Henny 1975), and although helpful in determining some aspects of dispersal, the information relies on band returns from the public and

is therefore somewhat biased. Information on an

individual's movements is not available, and locations where bands are recovered probably do not

accurately portray the individual's total movements. Biases occur with the area the dispersing

birds move through. In more populated areas, the

chances are higher that a bird will be recovered

or sighted. Bands as identification marks have

also been used in retrapping efforts on specified

study areas to determine dispersal between birthplace and breeding place (Newton and Marquiss 1983).

Such studies use data both from band returns from

the general public and from birds retrapped on the

study areas. Studies with confined sampling areas

provide an appraisal of juvenile dispersal that is

biased toward short-distance dispersers.

A distinct improvement is provided by radio telemetry, which reduces much of the bias of band

return studies by eliminating the reliance on a

confined study area and band returns from the

public. Radio telemetry has been used successfully for a number of years to study dispersal of

mammals (Phillips et al. 1972, Shirer 1968; Storm

and others 1976). Only recently has telemetry

been employed to gather detailed dispersal information on birds.

69
We discuss some of the problems encountered when

attempting to collect and interpret dispersal data

gathered in Oregon from juvenile northern spotted

owls (Strix occidentalis caurina). Actual data

used are preliminary and represent primarily a

single year's effort.

SPOTTED OWL DISPERSAL STUDY

Results from recent studies have shown that

northern spotted owls depend on old-growth forests

and are declining in numbers as these forests are

harvested (Forsman and others 1984, Solis 1983).

As the number of spotted owl pairs decreases and

the habitat becomes more sparse, the chances

increase for pairs or groups of pairs to become

reproductively isolated. Isolated owls do not

contribute to the maintenance of a diverse gene

pool. The distance between adjacent pairs or

groups of breeding owls must be such that dispersal and recruitment can replace losses (deaths or

emigrations) among existing pairs and provide for

colonization of suitable unoccupied habitats. A

study of dispersal should help formulate better

criteria for minimal spacing between pairs. Some

limited work on juvenile dispersal of spotted owls

has been reported from both Oregon and California

(Forsman and others 1984, Solis 1983). There are

studies currently underway in both California and

Washington (see respectively, Gutiérrez and others

1985 and Allen and Brewer 1985), as well as our

study in Oregon, to examine dispersal of juvenile

spotted owls in more detail.

In spring 1982, a radio-telemetry study was

initiated in Oregon to obtain dispersal information about the northern spotted- owl. Study

areas (fig. 1) were in the western hemlock (Tsuga

heterophylla [Raf.] Sarg.) zone of western Oregon,

an area dominated by Douglas-fir (Pseudotsuga menziesii [Mirb.] France) and western hemlock -

(Franklin and Dyrness 1973). Specific study sites

within the western hemlock zone were necessarily

determined by locations of nesting owls. Two

broad regions were chosen (the Cascade and Coast

Ranges), but specific study locations within these

regions necessarily changed from year to year.

Forests in the Cascades were less fragmented than

were those in the Coast Ranges.

In addition to addressing appropriate interpair

spacing, this dispersal study provided an opportunity to document other components of the species'

life history, such as breeding frequency, nesting

success, juvenile survivorship, and recruitment

Mortality of juvenile spotted owls has been

examined only briefly (Forsman and others 1984).

Age at first breeding and rates of recruitment to

the breeding population are unknown.

Collection of Dispersal Data

Life history characteristics of the spotted owl

create many of the limits to the study of

dispersal. For example, spotted owls lay relatively small clutches (l-3) and do not breed every

year (Forsman and others 1984). As a result,

researchers must work with small sample sizes of

KLAMATH \ I.

MOUNTAINS \ 1’

\

I /

I I I

I

r

.

i

J

Figure l--Northern spotted owl study areas in

western Oregon.

q.

B

dispersers. In addition, substantial mortality

occurs prior to dispersal (Forsman and others

1984), making it very difficult to follow significant numbers of dispersing juveniles. Forsman and

others (1984) document the fate of 29 young between the time of fledging and the end of August;

19 survived the interval, yielding a mortality

rate of 35 percent. We found mortality rates to

be the same with a similar sample size for an

equivalent time period. Use of radio transmitters

also allowed documentation of mortality for almost

an additional month up to the time of dispersal

(young owls began dispersal between 7 September

and 4 November). Mortality following fledging

rose to about 45 percent for this total predispersal period.

Thus, with a mean of two young fledged per successful nest (Forsman and others 1984), coupled

with the high predispersal mortality rate, an

average of one successful nest per "useful"

dispersing juvenile must be located. This is a ;;

formidable task, especially if study design dictates partitioning of the sample into various

categories (for example, habitat fragmentation

and stand ages). In 1983 we located 33 young that &

fledged from 19 successful nests. We relocated

these young at least weekly until young were large

enough to carry the transmitters. Twenty-five

70
young were still alive at the time transmitters

were put on (July-August) and 18 survived to

disperse.

Mortality seems to continue at a relatively high

2 rate during dispersal. Of the 18 juveniles that

survived to disperse, only 3 were still alive the

following May. Three other dispersers could not

be located, status undetermined.

T-i When radio signals for dispersing juvenile owls

were lost, extensive aerial searches were initiated to relocate them. If relocation was unsuccessful, we could not establish with certainty

whether the owls dispersed beyond the range of the

aerial searches (unlikely) or if their transmitters failed. Radio failure, although uncommon,

does occur. When a radio-marked disperser disappeared, for whatever reason, we faced a dilemma:

how to employ dispersal data for such individuals

up to the time of disappearance. The conservative

approach was to eliminate from the sample of

dispersers any owls that could not be accounted

for (disappear). Data gathered from such individuals could be incorporated into any summary of

dispersal so long as the bird was located throughout the period examined. Also, because such owls

were not necessarily dead, they could not be

incorporated into most mortality calculations

except under similar time constraints. The value

of all data acquired on any individual that eventually "disappeared" was greatly diminished

because there was no documented end point--

successful dispersal or death.

3

Short-term studies amplify the impact of the above

life history attributes. When trying to examine

dispersal in a quantitative rather than qualitak

tive way, the small sample size limits the significance of any statistical differences.

MEASURING DISPERSAL

End of Dispersal

Because of biological, logistic, and budgetary

limitations, projected sample sizes for a study of

owls will be small: An annual goal, for a

3-person field team, of 20-25 dispersing juveniles

is realistic. If the level of mortality we

observed is typical, few successful dispersers

will be documented. If an adequate number of successful dispersers is not available, then criteria

must be set to evaluate the level of resolution of

dispersal at hand. Various levels of defining

when dispersal ends can be adopted. Of these, the

most restrictive definition that the data will

permit should be selected. The following are

examples in decreasing order of resolution: (1)

owl is paired, breeds, and fledges one or more

-< young; (2) owl is paired during the breeding

season; (3) owl is settled in a definable area (3

months or longer) during the breeding season; (4)

owl is settled in a definable area (3 months or

J

longer) during the nonbreeding season; and (5) owl

disperses but dies before it has settled for 3

months.

In our study there are no juveniles in the first

two categories. Three juveniles fall into category 3, two into category 4, and eleven into category 5. As is evident from the data, it will take

several years of field study to obtain any sort of

sample size in the first two categories. Thus, it

may be necessary to adopt a less restrictive definition of dispersal in order to have a reasonable

sample to work with and to base management recommendations on. Both researchers and forest managers need to recognize these limitations and

jointly participate in deciding the level of resolution acceptable for management decisions.

Measuring Dispersal Distances

How to effectively measure dispersal distances or

to express dispersal depends on which role of

dispersal is examined. One role of dispersal is

as the mechanism that brings about gene flow.

Although all movements between birth site and

breeding site are important, as they contribute to

survival or lack thereof, only straight-line

distances between these sites measure dispersal as

it contributes to gene flow. In our study, juveniles have moved up to 76.8 km (straight-line

distance) from their birth site. But survival of

such long-distance dispersers has been low.

Dispersal, as it relates to gene flow, is functional only if the owl survives to breed. The

appropriate measure is the straight-line distance

between birth site and breeding site.

The other role of dispersal is the colonization of

vacant habitats. To determine encounter rates of

potentially vacant habitats by dispersing juveniles, total distance moved between birth site and

breeding site (summation of day-to-day movements)

are more appropriate than the straight-line

distance. If daily movements are determined,

these could be related to the type of habitats

encountered. Consideration of daily movements

allows other important characteristics of dispersal to be documented as well. Patterns of dispersal, such as the use or nonuse of major drainage

systems, can only be plotted through the total

movements of the juvenile.

Effective dispersal distance--Other researchers

have expressed dispersal distances in terms of the

number of home ranges moved across (Greenwood and

others 1979; Shields 1982). Shields (1982) states

that "dispersal distances are normally reported as

population averages of the absolute distances

individual propagules move. This erroneously

implies that dispersal is a continuous phenomenon,

ignoring the contributions of normal individual

spacing to dispersal." The individual spacing

that effects dispersal can be estimated from the

size of the home range. Effective dispersal

distance is the median dispersal distance divided

by the average diameter of the area occupied

exclusively by sedentary individuals (that is,

home range diameters). It is a term describing

dispersal in relation to home range size

(Greenwood 1980, Shields 1982). Effective dispersal distance thus does not provide a measurement

of distance but rather provides an index of population with respect to other populations or

71
Table l--Median and mean straight-line distances moved by spotted owls in west central Oregon (from natal

area to death or settling)

Dispersal Distances

Categories Sample Size Median Mean Minimum-maximum 4

Successful dispersers (fledged 1 or more young)

-------------Kilometers-------------

0 -- --

E

Owl is paired (breeding season) 0 -- --

Owl is settled (breeding season) 3 10.8 26.3 (4.8-57.9)

Owl is settled (nonbreeding season) 2 - 17.8 (14.8-20.8)

Owl disperses but dies before settling 11 24.0 33.4 (4.8-76.8)

species. Studies employing effective dispersal

distances have dealt with a more homogeneous

environment without the large gaps between pairs

of birds that are typical of the spotted owl. The

fragmented environment of the spotted owl does not

lend itself to expressing dispersal distance in

this manner.

Mean vs. median dispersal distances--When

straight-line distances are used to express

dispersal, should they be averaged? Shields

(1982) points out that by averaging the distances,

the few long-distance dispersers inflate the mean

dispersal distance. This leads to an overestimation of the distance the typical individual moves.

He suggests using the median dispersal distance

instead. Using our 1983 sample, we calculated

both mean and median dispersal distances (table 1)

for the categories discussed in determining when

dispersal ends. Median dispersal distances were

substantially less than the mean, and we feel the

median better represented the typical individual's

movements.

Dispersal-Related Questions

Other dispersal-related questions requiring attention include differential dispersal by sex, population density effects on dispersal distances and

success, initiating and terminating factors for

dispersal, and yearly variation in dispersal. In

a short-term study, some of these questions cannot

be adequately addressed. For the spotted owl in

particular, an especially important question might

be "what effect does fragmentation of the habitat

have on dispersal and the foraging behavior, habitat use, and survival of dispersers?" One of the

main problems with determining fragmentation

effects is devising an appropriate measure of

fragmentation. Work with habitat fragmentation

presents the investigator with all the problems

associated with an uncontrolled experiment: The

various arrays of fragmentation were not designed.

If active nests are located in a variety of

fragmented regimes, a control area should exist

that has little or no fragmentation. Spotted owl

movement capabilities seem, unfortunately, to be

great enough to thwart any attempt to utilize

existing landscape patterns, even national parks

or wilderness areas. Dispersing juveniles are

likely to pass through several levels of habitat

fragmentation, thereby frustrating attempts to

differentiate which fragmentation pattern has what

effect.

Many investigators have documented that for most

birds, females predominate among long-distance

dispersers. To test whether or not this is also

the case for the spotted owl, one must be able to

correctly identify the sex of juveniles. Criteria

used in the past to identify the sex of juvenile

spotted owls (weight and wing measurements) are A

not particularly reliable. In a recent paper,

Barrows and others (1982) suggest determining sex

of spotted owls by inspection of the barring pattern on the middle tail feathers. Of 11 carcasses ,e

for which we were able to check tail feathers

against an internal examination, the pattern of

tail feathers correctly identified the sex of the

juvenile in each case. The success of this technique should help answer the differentialdispersal-by-sex question for the spotted owl.

SUMMARY

The problems presented here are not new and are

common to any study of dispersal. The spotted

owl, because of its low density, sporadic reproduction, and small clutch sixes, presents a significant problem to dispersal studies --small

sample size or high cost per unit of data.

The acceptable resolution level of dispersal and

measurement of dispersal distances are closely

tied to sample size. With a limited sample, it

may not be possible to focus only on the successful dispersers. The longer the issue is studied

on a continuous basis, the more the abovementioned problem will be alleviated. "%

Especially in short-term studies, the major

question becomes how much information is enough.

There must be a consensus among researchers and F

managing agencies, such as the State and Federal

fish and wildlife agencies, USDA Forest Service,

and the Bureau of Land Management, as to what

72
constitutes an acceptable data set to base management decisions on. The agencies that will employ

the information are necessarily responsible for

determining the longevity of the studies and the

size of the sample.

ACKNOWLEDGMENTS

Robert Anthony, Ruth Brandt, Andrew Carey, Eric

Forsman, and R. J. Gutiérres reviewed various

drafts. Paul Opler, U.S. Fish and Wildlife

Service, provided a constructive review as well.

Their comments added greatly to the manuscript.

This study was conducted under the auspices of the

Oregon Cooperative Wildlife Research Unit with

Oregon State University, Oregon Department of Fish

and Wildlife, U.S. Fish and Wildlife Service, and

the Wildlife Management Institute cooperating.

Funding for this research was provided by the

Old-Growth Forest Wildlife Habitat Program, USDA

Forest Service, Pacific Northwest Forest and Range

Experiment Station, Contribution No. 26. This is

Oregon State University Agricultural Experiment

Station Technical Paper 7264.

LITERATURE CITED

Allen, H.; Brewer, L.W. A review of current

northern spotted owl (Strix occidentalis

caurina) research in Washington State. In:

Gutiérrez. Ralph J.; Carey, Andrew B., tech.

eds. Ecology and management of the spotted owl

in the Pacific Northwest. Gen. Tech. Rep.

PNW-185. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest

Forest and Range Experiment Station; 1985:

55-57.

Barrows, C.W.; Bloom, P.H.; Collins, C.T. Sexual

differences in the tail barring of spotted owls.

North American Bird Bander. 7: 138-139; 1982.

Erickson, M.M. Territory, annual cycle, and numbers in a population of wren-tits (Chamaea

fasciata). University Calififornia Publication

Zoology. 42: 247-334; 1938.

Forsman, E.D.; Meslow, E.C.; Wight, H.M.

Distribution and biology of the spotted owl in

Oregon. Wildlife Monograph. 87; 1984. 64 p.

Franklin, J.F.; C.T. Dyrness. Natural vegetation

of Oregon and Washington. Gen. Tech. Rep.

PNW-8. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Forest and Range Experiment Station; 1973. 417 p.

Gibb, J. Population changes in titmice, 1947-1951.

Bird Study. 1: 40-48; 1954.

Greenwood, P.J. Mating systems, philopatry, and

dispersal in birds and mammals. Animal Behavior.

28: 1140-1162; 1980.

Greenwood, P.J.; Harvey, P.H.; Perrins, C.M. The

role of dispersal in the great tit (Parus 

major): the causes, consequences and heritability of natal dispersal. Journal of Animal

Ecology. 48: 123-142; 1979.

Gutiérres R.J.; Franklin, Alan B.; LaHaye,

William; Meretsky, Vicky J.; Ward, J. Patrick.

Juvenile spotted owl dispersal in northwestern

California: preliminary results. In: Gutiérrez,

Ralph J.; Carey, Andrew B., tech. eds. Ecology

and management of the spotted owl in the Pacific

Northwest. Gen. Tech. Rep. PNW-185. Portland,

OR: U.S. Department of Agriculture, Forest

Service, Pacific Northwest Forest and Range

Experiment Station; 1985: 60-65.

Horn, H.S. Some theories about dispersal. In:

Swingland, I.R.; Greenwood, P.J., eds. The ecology of animal movement. Oxford University

Press; 1983. 54-59.

Houston, C.S. Recoveries of Saskatchewan-banded

great horned owls. Canadian Field-Naturalist.

92: 61-66; 1978.

Howard, W.E. Innate and environmental dispersal

of individual vertebrates. American Midland

Naturalist. 63: 152-161; 1960.

Johnston, R.F. Population structure in salt marsh

song sparrows. Part 1. Environment and annual

cycle. Condor. 58: 24-44; 1956.

KLuijver, H.N. The population ecology of the great

tit, Parus m.major L. Ardea. 39: 1-135; 1951. - -

Lidicker, W.Z. Emigration as a possible mechanism

permitting the regulation of population below

carrying capacity. American Naturalist. 96:

29-33; 1962.

Newton, I.; Marquiss, M. Dispersal of sparrowhawks between birthplace and breeding place.

Journal of Animal Ecology. 52: 463-477; 1983.

Phillips, R.L.; Andrews, R.D.; Storm, G.L.;

Bishop, R.A. Dispersal and mortality of red

foxes. Journal of Wildlife Management. 36:

237-248; 1972.

Shields, W.M. Philopatry, inbreeding and the evolution of sex. Albany, NY: State University of

New York Press; 1982. 245 p.

Shirer, H.W.; Downhower, J.F. Radio tracking of

dispersing yellow bellied marmots. Transactions

of the Kansas Academy of Science. 71: 463-479;

1968.

Solis, D.M. Summer habitat ecology of the

northern spotted owl. Arcata, CA: Humboldt

State University; 1983. M.S. thesis. 168 p.

Storm, G.L; Andrews, R.D.; Phillips, R.L.; Bishop,

R.A.; Sinoff, D.B.; Tester, J.R. Morphology,

reproduction, dispersal, and mortality of midwestern red fox populations. Wildlife Monograph.

49; 1976. 82 p.

Stuart, P.A. Dispersal, breeding behavior, and

longevity of banded barn owls in North America.

Auk. 69: 227-245; 1952.

VanCamp, L.F.; Henny, C.J. The screech owl: its

life history and population ecology in northern

Ohio. North American Fauna No. 71; 1975. 65 p.

73
THE DEMOGRAPHY AND POPULATION GENETICS OF OWLS, 

WITH SPECIAL REFERENCE TO THE CONSERVATION 

OF THE SPOTTED OWL (Sm occidentalis) 

George F. Barrowclough and Sadie L. Coats 

ABSTRACT: Data are summarized on the density, dispersal, demography, and 

genetic structure of several species of owls. Life history traits for the 

majority of these species are such that the effects of variance in 

reproductive success and overlapping generations act to reduce effective 

population size with respect to census size by as much as 50 percent. 

Estimates of effective deme sizes vary over several orders of magnitude; 

for four of six species, the effective sizes are on the order of lo2 to 

103. The genetic structure of spotted owl, str1x occidentalis, 

populations in the Pacific Northwest consists of a continuum of 

neighborhoods isolated by distance from each other. We estimate that 

currently there are approximately 10 such units, each composed of about 220 

effective individuals, in the range of the subspecies caurina. A management 

plan to preserve the species in that region will result in the preservation 

of a network of habitat patches. The effects such a plan will have on 

genetic structure and level of inbreeding depend critically on the level of 

occupancy of the preserved areas. Estimates of this occupancy rate are not 

available, but a method is outlined to evaluate genetic structure given 

such estimates or a model of population dynamics. A "best case" example is 

given along with some recommendations for data that are critically needed 

for evaluating the actual effects of a spotted owl management plan. 

INTRODUCTION 

The purpose of this paper is to describe and 

analyze, to the extent possible, the patterns 

of demography and population genetics of owls. 

Special emphasis is placed on the spotted owl, 

Strix occidentalis, a subject of current 

interest because of concern about the species' 

status in old-growth forests of the Pacific 

Northwest. 

GEORGE F. BARROWCLOUGH is Assistant Curator and 

SADIE L. COATS is Associate in the Department 

of Ornithology of the American Museum of 

Natural History, New York, N. Y. 

It appears likely that much of the old-growth 

forest that constitutes the prime habitat for 

the spotted owl will be regularly harvested for 

timber: thus, the survival of the bird in this 

part of its range may depend on the maintenance 

of Spotted Owl Management Areas (SOMAS) in the 

National Forests of the region. The efficacy of 

these habitat patches as a mechanism for 

preserving the spotted owl in the Pacific 

Northwest will depend not only on the number, 

size, geographical location and quality of these 

areas, but also on the demographics (survivorship, fecundity, and dispersal schedules) and 

genetics of the species (Shaffer 1981). These 

aspects of the biology of a species can be 

analyzed using the techniques of population 

ecology and population genetics. Population 

ecologists can aid wildlife managers by 

investigating the way a species' demography, 

74 
dispersal patterns, and geographic distribution

may interact with environmental factors and

ecological perturbations. Models can then be

developed for predicting long-term probability

of survival. Shaffer (1985) addresses these

issues. Geneticists use these same variables and

the equations of population genetics to investigate the genetic structure and likely pattern

of inbreeding in the population. We address that

topic here.

It is widely understood that inbreeding can be

detrimental. It can lead to reduced numbers of

offspring, poorer quality offspring, and a

generally reduced vigor of the individuals in a

population. These effects are discussed in

Frankel and Soulé (1981). A general conclusion

of such analyses is that inbreeding, if severe,

can lead to inviability of a population and to

its eventual extinction. Hence, an important

goal of any attempt to maintain a natural population through management must be the monitoring and regulation of inbreeding.

The extent of inbreeding in a. population can be

measured directly--for instance -by using molecular genetics techniques such as. electrophoresis

(for example, Patton and Feder 1981); however,

these methods only yield estimates of the current level of inbreeding. To predict how inbreeding will progress, a model of the genetic

structure of the population must be developed.

By genetic structure, we refer to the geographic

continuity of populations--over what geographic

area a population can be considered randomly

mating, and how many individuals can be found in

that area. The models used to develop guidelines, such as preserving 50 individuals to

prevent inbreeding in excess of 1 percent per

generation (Frankel and Soulé 1981), are based

on the assumption of no geographical structure;

that is, on complete panmixia of the population.

Such an assumption is reasonable for zoos, but

not necessarily for a wild population spread

over large expanses of a continent.

Researchers concerned with the population dynamic aspects of conservation have explicitly

examined the role of geography on the probability of long-term maintenance of a population

(see, for example, Shaffer 1985). However,

population geneticists concerned with conservation genetics have not devoted equivalent

attention to this problem. In this study we

begin a first attempt to incorporate this

important biological reality into conservation

genetic analysis.

Much remains to be learned about the natural and

life histories of owls,. including the spotted

owl. In spite of this lack of complete data,

however, management plans are now being developed. To assess whether any particular proposed

Spotted Owl Management Plan (SOMP) will be

successful over some extended period of time, it

is necessary to predict the response of the owls

to the details of the plan. This necessitates

the rapid development of models for the population dynamics and genetics of spotted owls.

Thus, it seems requisite to beqin organizing our knowledge of owl demographics and

genetics now, even though data are limited. Data

from future studies, as well as from projects

currently underway, will no doubt refine estimates of parameters and lead to some modifications of results and conclusions; nevertheless, it is equally true that the simple,

preliminary results of these analyses and models

will identify key life history parameters that

require immediate intensive investigation.

Finally, we believe it is important to summarize

inferences that currently can be made about the

demography and genetics of owls in general and

to make these data available to the community of

researchers interested in the dynamics and

genetics of natural populations.

METHODS AND RESULTS

Our analysis of the demographics of owls requires the estimation of population density and

the distributions of three life history parameters--survivorship, fecundity, and dispersal.

From these data, a life table can be constructed; such a table is essential for most approaches to modeling population dynamics. These

same data are needed for modeling the genetic

structure of a population.

Several models of geographic population structure may be relevant to avian species. The

various models and instances of their use in

studies of birds have been reviewed by

Barrowclough (1980) and Rockwell and

Barrowclough (in press). A basic distinction

must be made between species that are geographically isolated in colonies or "islands" of

habitat, and those that are more or less

continuously distributed throughout their range.

For the spotted owl, as well as for most other

owls, the latter model appears to be more

reasonable. For such cases, even though the

species' distribution is considered continuous,

there is expected to be some genetic differentiation across the range simply because

dispersal of young birds, from their natal site

to the location where they breed as adults, is

finite. Depending on the strength of the

tendency for offspring to nest in the vicinity

of the site where they were raised (philopatry),

it may take several, or even many, generations

for genes to "flow" across the range of the

species. Continuously distributed populations of

birds are therefore said. to be "isolated by

distance.” The genetic structure of such species

is modeled by determining the geographical area

over which allelic frequencies should be nearly

uniform--this requires information about

dispersal--and estimating the number of birds in

such an area--which requires estimates of

density. The "effective population size" (Ne)

of this area of the total species’ range is

derived by estimating how such factors as

population fluctuations, sex ratio, and life

expectancy and fecundity schedules affect the

dynamics of genes within the local population.
The effective population size of the local unit

(deme) is the number of genetically ideal (randomly mating, discrete generations, Poisson

variance of offspring numbers, etc.) individuals

that would have evolutionary properties equivalent to those of the actual individuals in the

deme with their real, biologically complicated

demographic schedules. Once the theoretical

effective size of a deme of continuously distributed organisms is known, it is possible to

make some predictions about the extent of

inbreeding in the population.

The estimation of the genetic structure of

natural populations using demographic data, as

with any complicated modeling approach, is based

on a 'number of biological and mathematical

assumptions. These assumptions are discussed in

some detail in Rockwell and Barrowclough (in

press).

Calculations. The specific method used to

obtain statistics describing. the genetic structure of spotted owl populations originated with

Dobzhansky and Wright (1943, 1947), who worked

on Drosophila. The method subsequently was

modified for use on avian populations by

Barrowclough (1980). We estimate the effective

size, Ne, of current spotted owl demes as the

number of randomly mating individuals equivalent

to the number of owls actually present in a

circle with a radius twice the dispersal distance of juveniles. In summary:

Ne

= 4 π p s

2FRF

RSFGT ;

where p is the density of spotted owls throughout the area over which dispersal occurs, σ is

the root-mean-square dispersal distance for

juveniles, and FRS and FGT are factors that

correct for departures from the random transmission of genes from generation to generation

caused by the effects of variation among pairs

in reproductive success, and the influence of

overlapping generations, respectively. F

K corrects the geographical size of the deme for the

effects of non-normality of the dispersal distribution.

A. Dispersal.--Spotted owls are nocturnal and

difficult to study; consequently, quantitative

data for the species are just starting to be

accumulated, and we were forced to use data and

estimates of life history parameters from a

number of different sources. Data resulting from

radio-tracking juvenile and adult spotted owls

in northern California for several

(Gutiérrez and others 1985, unpubl. data 1

/),

allow estimation of the dispersal distribution

of juveniles and information on survivorship of

both juvenile and adult spotted owls.

1

/ Data on file with R. J. Gutiérrez,

Department of Wildlife Management, Humboldt

State University, Arcata, CA 95521.

Table l--Summary of dispersal distances of

juvenile spotted owls, based on radio-tagging

within northwestern California

Distance, di (km) O-25 26-50 51-75 76-100

Number, n 3 6 3 1 .\i

If the distances juveniles moved (between the

sites where they were hatched and where they

breed as adults) were random with respect to

direction and normally distributed with respect

to distance, then approximately 87 percent of

all genes at a particular point would come from

within two standard deviations of the distribution of dispersal distances from that point.

Thus, a standard measure of Ne for continuously distributed organisms is the effective

size of the population within a circle of radius

2 σ (Wright 1969). The root-mean-square dispersal

distance, σ , is the standard deviation of

juvenile dispersal distances about their nest

site (origin); σ

2

is the variance of such

distances. Dobzhansky and Wright (1947) showed

that:

s = √ [(1/2N) ∑ d

2/1]:

where N is the total number of juvenile owls

studied and di is the distance dispersed by

the ith juvenile. For the study by Gutiérrez

and others (1985), the distribution of juvenile +I.

dispersal distances is summarized in table 1.

σ , computed as described above, was found to be

33.56 km for the 13 radio-tagged juveniles.

These data may somewhat underestimate true

dispersal distances because some of the owls in *

the study may have died before finishing their

dispersal; additionally, the batteries in some

of the transmitters may have failed before

dispersal was ended. More dispersal data are

needed; at present these are the best data

available and suggest that actual dispersal is

roughly 30-40 km. It would be desirable to have

dispersal distances based on a large sample of

birds followed from their birth site to their

actual breeding site.

B. Density.--To obtain a realistic estimate of

effective deme size, one should have an estimate

of density from the same region from. which the

dispersal distance data were obtained. This is

because there is the possibility that density

and dispersal may covary. That is, dispersing

birds may tend to move further in areas of low

density (poor habitat). Data on the density of

spotted owls in northern California where the

radio-tagging

ed. 2/

is being performed were obtain2

/ Data compiled by G. I. Gould, Jr., Wildlife _

Management Branch, Department of Fish and Game, 5

1416 Ninth St., Sacramento, CA 95814.

76
There are approximately 558 territories in the

area bounded by the Pacific Ocean on the west,

the Oregon border on the north, the northern

border of Mendocino County on the south, and a

line on the east running north-south through the

town of Yreka. It was estimated that 90 percent

of the 558 territories were occupied by pairs of

owls and the remaining 10 percent by single

birds: in 28,990 km2

 of northern, coastal

California, there are about 1060 owls, or an

approximate density of 0.037 owls per km2

.

This estimate is of average density over good,

poor, and completely unsuitable habitat. It is

necessary to use this estimate rather than one

for strictly good habitat because the dispersal

of juveniles takes them through mixes of habitat

types, and the geographical area occupied by a

single deme of spotted owls will include unsuitable habitat.

C. Life table.--A life table is perhaps the most

important abstraction required in modeling the

population dynamics of a species. It is also

needed for modeling population genetics because

it provides the information requisite for estimating the effects of delayed breeding and

overlapping generations. There are two critical

aspects to the estimation of a life table: data

are needed on year-to-year survivorship and on

fecundity.

1. Survivorship.--Survivorship was estimated

using the results of the radio-tagging undertaken by Forsman and others (1984) and by

Gutiérrez and others (1985). First, for adult

spotted owls, it was noted that there were five

deaths in 33 owl years of monitoring; this is

based on 20 owls that were tracked for periods

of 1 to 3 years and six others that were tracked

for periods of roughly 4 months. Thus, yearto-year survivorship was approximately 0.85. We

assumed that avian lifespans are exponentially

distributed (for example, Deevey 1947); survivorship was therefore assumed to be constant for

the second year of life on.

Survivorship of juveniles was more difficult to

estimate. We again used data from radio-tracking

of juveniles in northwestern California. Because

of the short timespan over which owls have been

tagged, and the high mortality rate, we estimated survivorship separately for each 3-month

period of the first year, beginning at the time

of fledging. For the first 3 months, 3 out of 13

tagged birds died: this is a period of time when

the juveniles are still partially dependent on

their parents for food. Survivorship (sx)

during this interval was estimated as 10/13, or

0.77. During the next 3-month period, when

dispersal occurs and winter begins, 4 of 10

tagged birds died: thus, we took sx to be

8.60. For the winter months, 3 of 6 birds

apparently died: consequently, sx was assumed

to be 0.50. No data were available for the last

3 months of the first year of life. During this

period of time, spring, prey should become

abundant; hence we estimated that the probability of death would be of the order of

one-half the rate during the previous 9 months.

The average death rate, per 3-month period over

Table 2--Distribution of reproductive success

among pairs of spotted owls

No. of fledglings (x) 0 1 2 3 4

No. of pairs (p) 73 16 26 4 0

Source: Forsman and others (19841.

the first 9 months, was 0.38; the average sx

over this period was 0.62. Thus, for the last

3-month period, we estimated the death rate to

be 0.19; this yields an sx of 0.81. Consequently, we estimate first year survivorship of

spotted owls as (0.77)(0.60)(0.50)(0.81) or

0.19. This estimate has an unknown, but probably

substantial, standard error associated with it;

it is likely that only about one out of five to

one out of ten fledged spotted owls survive

their first year.

2. Fecundity.--We estimated a mean and a variance of fecundity using the data reported by

Forsman and others (1984), which was based on

their study of the spotted owl in Oregon. We

measured fecundity as the number of fledged, or

nearly fledged, offspring observed at a nest.

This measure of fecundity conforms to the

survivorship period of the life table, which

starts at the time of fledging. The numbers of

offspring produced by 119 pairs are shown in

table 2; a total of 80 young were produced.

Thus, each pair produced an average of 0.67

offspring per year. If a 1:l sex ratio is assumed, then this is equivalent to 0.34 female

offspring per female per year. The variance of

reproductive success among pairs, computed from

the same distribution of fecundities, is:

VRS = [ ∑ px

2

−(∑ px)2/N]=(N-l) = 0.87;

where x is the number of fledglings produced by

a pair, p is the number of pairs producing that

number of fledglings, and N is the total number

of nests observed. We assume spotted owls do not

breed their first or second spring: this is generally consistent with life history studies and

other, anecdotal information in the literature.

It is probably true that some 2-year-olds attempt to breed: also, however, probably not all

3-year-olds do: further study of radio-tagged,

known-age birds is warranted.

We stress that the life table for the spotted

owl, based on these calculations (table 3), must

not be taken as definitive, given the uncertainty associated with much of the data. Nevertheless, it should prove useful as a first

approximation in initiating analyses of the

dynamics and genetics of the species.

D. Generation time.-- Age-structure will influence the effective size of a local population.

For example, Dobzhansky and Wright (1943)

explicitly discuss this problem, and human

demographers have devoted much effort to

analyses of the magnitude of the effect (for

example, Emigh and Pollack 1979). Emigh and

Pollack present an algebraic method for

77
Table 3--Life table for the spotted owl: fecundity is measured as number of female

offspring per female

Age (x) 0 1 2 3 4 5 6 7 8 9 10

Survivorship (sx) 1.00 0.19 0.85 0.85 0.85 0.85 0.85 0.85 0.85 0.85 0.85

Fecundity (bx) 0 0 0 0.34 0.34 0.34 0.34 0.34 0.34 0.34 0.34

correcting estimates of effective population

size for the effects of age-structure, delayed

breeding, and overlapping generations.

We have used the life table for spotted owls

(table 3) as input to a computer program that

calculates the magnitude of this effect. The

result is a factor, FGT, that represents the

ratio between effective size and the census

number of individuals. For the spotted owl, the

result is FGT = 0.69. The fraction, for this

life table, is considerably less than one, indicating an important effect. This is because we

have assumed that the density figures are for

territorial, but not necessarily breeding,

birds; that is, some l- and 2-year-old birds are

present in the population, respond to calling

(and so are included in the density estimates),

but do not breed. The F

GT factor corrects for

the fact that the census density includes

prereproductives, and consequently is greater

than the number of individuals contributing to

the gene pool at any given time. In theory this

factor can vary from zero to two; if only

reproducing individuals were included in the

density figures, then FGT for this life table

would be close to one.

E. Variance in reproductive success.--An underlying assumption of estimates of effective

population size is that the variation in reproductive success among pairs of individuals has a

Poisson distribution; that is, that the variance

of the distribution is equal to its mean. This

is an empirical question, however, and it

appears that in a number of species, at least of

birds, the variance exceeds the mean. Such is

the case for the spotted owl, in which our

estimate of the mean fecundity is 0.67, and its

variance is 0.87 (see above). Again, as with the

problem of age-structure, it is possible to

compute a correction factor to estimate the

effective size of a population with a given

distribution of fecundities. The formula is

given by Crow and Kimura (1970): the ratio of

effective to actual number of individuals is

computed as:

F

RS = X/[X-l+(VRS/x) ];

where x is the mean number of fledglings per

pair, and V

RS is its variance. For the spotted

owl, x is 0.67, VRS is 0.87, and FRS is 0.69.

F. Kurtosis of dispersal.--An additional assumption that requires attention in the computation

of effective deme size is that of a normal

distribution of juvenile dispersal distances. In

fact, as Bateman (1951) points out, dispersal

distance distributions depart to some degree

from normal in almost all organisms. (Distributions may be characterized as leptokurtic or

platykurtic. In a leptokurtic distribution,

there are more short- and long-distance dispersers and fewer intermediate-distance dispersers -than would be expected in a normal

distribution. In a platykurtic distribution

there are an excessive number of intermediatedistance dispersers over the expectation of a

normal distribution, but fewer short- and

long-distance dispersers.) The distribution of

dispersal distances for the spotted owl (table

1) is slightly platykurtic, with a coefficient

of kurtosis of -1.07. Using the above estimate

of kurtosis, we estimate a deme of owls, due to

this departure from normal dispersal of juveniles, actually occupies an area slightly

smaller than the circle of radius 2 σ. The

actual size of this area is reflected in the

kurtosis factor, F

K, computed using the

relationship developed by Wright (1969,

p. 304-305). For the spotted owl, we obtain an +.

estimate of FK of 0.81.

G. Effective deme size.--Given the results of

the above analyses, it is possible to compute an

estimate of effective population size of a deme 3

or neighborhood using the formula presented

earlier:

Ne

= 4 π σ

F

K FRS FGT.

Thus,

Ne

= 4 Π (0.04km-2)(33.56km)2(0.81)(0.69)(0.69)

= 218.23.

This is an estimate of the effective size of

local populations of spotted owls under current

conditions.

An additional point is worth noting. FRS was

defined as the ratio of effective size to census

size that corrected for the effect of a nonrandom (non-Poisson) contribution of genes from

individuals of one generation to the next

because of variance among individuals in reproductive success. F

GT was defined as the ratio

of effective size to census size that corrected

for the fact that generations are not discrete :s

and that prereproductive owls are included in

estimates of density. Consequently, the overall

ratio of genetical effective population size to

census number for spotted owls must be the 2

product of F

RS and F

GT, or 0.48. This

implies that to have an effective population

size of any particular number of spotted owls,

it is necessary to have a census number of

78
Table 4--Estimates of density for several

species of owls

Species p (km-2) Reference

Tyto alba

Otus asio

0.08 Sharrock (1976)

0.30 Craighead and Craighead

(1969)

Bubo bubo 0.01 Olsson (1979)

B. virginianus 0.15 Craighead and Craighead

(1969)

Strix aluco 0.40 Sharrock (1976)

adults l/0.48, or 2.10, times as large. For

example, an effective population of 500 owls

would require a census number of 1,042 owls.

The fact that the effective size of populations

is usually substantially less than the census

size has now become widely recognized by geneticists and wildlife managers [Frankel and Soule

1981). Thus, the result reported above should

not be particularly surprising. Two additional

factors with potential effects on this same

ratio have not been considered here, but should

be kept in mind. First, we have implicitly

assumed a 1:1 sex ratio for breeders. If the sex

ratio differs from this, then effective size

will decrease further. Second, we have assumed

that the owl populations are numerically constant and do not fluctuate. If they do fluctuate, about some mean, then the overall Ne to

NC ratio will again be reduced and will be

biased toward the minimum size (for example,

Crow and Kimura 1970, p. 109-110).

H. Genetic structure and inbreeding.--Inbreeding

is a complex, hierarchical topic. The general,

underlying concept concerns the correlation of

individual alleles within individuals. That is,

in diploid organisms, such as birds, each

individual has two copies of each gene. If more

than a single allele segregates at a locus in

the species, then the probability that the two

genes in an individual will be identical can be

computed, for a randomly mating population,

based on the frequencies of the alleles. If

there are departures from random mating, however, then the probability of the two copies of

the gene being identical may increase and the

individual is said to be inbred; that is, there

is a positive correlation of identity of the two

copies of a gene within an individual. The

departures from random mating may be of two

types. First, there may be an increased likelihood of close relatives mating: this is the

notion of inbreeding in common usage. It is

sometimes identified by the symbol FisSecond, if the entire population of the species

is not panmictic, but rather is organized into

isolated colonies or even more or less continuously distributed neighborhoods (demes),

then the copies of the same gene in an individual will be correlated merely due to the

geographic structure of the population inhibiting the thorough mixing of genotypes in each

generation. Here we refer to the magnitude of

this effect by the symbol Fst.

Our computations suggest that the genetic

structure of spotted owl populations in the

Pacific Northwest is characterized by neighborhoods of approximate effective size of 220

individuals. These demes are not discrete

entities, but continuously grade into each

other; they each occupy a geographical area of

diameter 4 σ√ FK, Or approximately 120 km.

Thus, in the range of the subspecies S. o.

caurina in Washington, Oregon, and California,

there are probably on the order of 10 demes.

This is a very rough approximation based on

geographical distance and area. It is consistent

with a current total census population of about

5,000, and a total effective size, summed over

demes, of about 2,500. These estimates are

probably correct to within a factor of two or

so, and will be sufficient for illustrative

calculations.

Wright (1969, p. 299-303: see also Rockwell and

Barrowclough in press) provides a method for

estimating levels of correlation of genes within

demes (Fst inbreeding) that are isolated by

distance, relative to the total population. For

a series of 10 demes each of size 220, Fst is

estimated to be about 0.007.

DEMOGRAPHY AND GENETICS OF SELECTED SPECIES OF

OWLS

We examined literature on life history, ecology,

and behavior of birds to obtain comparative

results for other species of owls. This survey

was made partly to ascertain whether our estimates of spotted owl parameters were reasonable,

but also to explore the demography and genetics

of a number of species of an avian order and

make the results available to ornithologists and

population ecologists.

We found sufficient data to compute estimates of

life tables and effective deme sizes for five

additional species of owls: Tyto alba, OtUS

asio, Bubo virqinianus, B. bubo, and - StrixAluco. Of necessity, data from more than one

study had to be combined in the analysis of some

of these species. Where possible, data used for

a species were all from the same geographic

region. Data for Tyto alba, - - the barn owl, are

from England, except for fecundity and survivorship values which come from studies in the

United States. Data for Otus asio, the eastern

screech-owl, come from northern Ohio and

southern Michigan. Data for Bubo bubo, the Old

World eagle owl, derive from studies in

southeastern Sweden, and Germany and adjacent

northern Austria. Density figures for Bubo

virginianus, the great horned owl, come from

southern Michigan; the data for productivity,

dispersal, and survivorship are from birds

breeding in Saskatchewan. All data for Strix

aluco, the tawny owl, are from near Oxford,

79
Table 5--Distribution of dispersal distances for selected species of owls

Species Distance and number dispersing 1/ Reference

Tyto alba X 5 30 75 150 250 Bunn and others (1982)

- -

f(x) 98 68 9 8 1

Otus asio X 8 24 40 56 105 185 233 298 Van Camp and Henny (1975)

f(x) 25 21 3 2 1 1 1 1

Bubobubo - - X 25 50 75 Olsson (1979)

f(x) 8 5 3

B. virginianus x 5 26 81 185 315 710 908 1062 Houston (1978) -

f(x) 18 17 23 11 3 4 3 2

Strix aluco X 0.7 1.5 3.5 7.2 20 Southern (1970) - -

f(x) 3 1 2 1 2

1

/ f(x) is the number of individuals banded as nestlings and recovered, when old enough to

breed or hold a territory, x kilometers from their nestsite.

Table 6--Mean and variance of reproductive success among pairs in selected species of owls

Species

Number of young fledged per pair

0 1 2 3 4 5 6 X

V

RS Reference

Tyto alba 31 11 18 22 22 10 1 2.23 3.02 Bunn and others (1982)

Bubobubo 22 10 8 7 0 0 0 1.00 1.26 Frey (1973)

B. virginianus 82 78 121 84 6 0 0 1.61 1.23 Henny (1972)

-- Strix alucol/- 8 3 2 3 1 0 0 1.18 1.90 Southern (1970)

a

1/ Data from 1947 study year.

England, except the density figures, which are

an average over all of England, Scotland, and

Wales.

Data for density, dispersal, and reproduction

are listed, with their sources, in tables 4, 5,

and 6. Tabulated values were mostly taken directly from the literature, but in some cases

estimates of requisite parameters were not

available and were calculated using published

information. σ , VRS, and factors F

K and

F

RS were computed as for the spotted owl.

Dispersal distances in table 5 are not uniform

across species because of the way that data are

reported in the original literature. The values

shown are the midpoints of the reported intervals. Data for among-pair variation in number of

fledglings produced by 0tus asio were lacking,

so the mean of the other five VRs estimates

was used for that species.

Estimates of life tables for the five species of

owls are shown in table 7. All are arbitrarily

truncated at 10 years. The estimates of fecundity are based on data in table 6 except for

- - Otus asio and Strix aluco; a 1:l sex ratio is

assumed and bx is given as female offspring

per female. For Otus, the complete life table is

that computed by Ricklefs (1983). For Strix, the

data in table 6 are for a single year, 1947, of

Southern's study (1970). The estimate of bx in

table 7 represents an average for the tawny owl

over 13 study years. To compute year-to-year

survivorship, we computed ratios of returns of

banded birds from consecutive years. Juveniles

were treated as a separate class. In cases for

which adequate returns were available, first

year birds were also treated separately. These

life tables are all rough approximations, but

are adequate for the calculation of F

GT, which

was their intended purpose.

Table 8 contains estimates of effective deme

sizes and several other parameters relevant to

the genetics of natural populations. The estimates were computed as described above for the

spotted owl. There is substantial variation of

the estimates of Ne among species. The principal factors contributing to the variation

appear to be dispersal distances, density, and

the factor reflecting variance in reproductive

success among pairs (FRs). The results for the

great horned owl indicate an exceptionally large :i

value of Ne; this reflects the estimate of

dispersal that is an order of magnitude greater

than those for the other species. The sample

sizes in Houston's (1978) study were not small; 2

however, the result is influenced by a few very

long distance dispersers. Thus, the estimate is

probably a bit on the high side. For example, if

80
Table 7--Life tables for selected species of owls

3

I

i

Age (x)

Species 0 1 2 3 4 5 6-10 Reference

TYto alba - -

Otus asio

Bubobubo - -

B. virginianus,

Strix aluco ---

s x

1

/ 0.35 0.57 0.63 0.63 0.63 0.63 0.63

bx

2

/ 0.00 1.12 1.12 1.12 1.12 1.12 1.12

SX 0.31 0.59 0.63 0.67 0.75 0.75 0.75

bX 0.00 1.04 1.30 1.30 1.30 1.30 1.30

SX 0.44 0.67 0.67 0.67 0.67 0.67 0.67

bX 0.00 0.00 0.50 0.50 0.50 0.50 0.50

SX 0.42 0.56 0.67 0.67 0.67 0.67 0.67

bX 0.00 0.00 0.80 0.8O 0.80 0.80 0.80

SX 0.47 0.79 0.82 0.82 0.82 0.82 0.82

bX 0.00 0.35 0.35 0.35 0.35 0.35 0.35

Stewart (1952)

Bunn and others

(1982), Henny (1969)

Ricklefs (1983)

Ricklefs (1983)

Rockenbauch (1978)

Frey (1973)

Houston (1978)

Henny (1972)

Southern (1970)

Southern (1978)

1/ Year-to-year probability of survival.

2/ Female offspring per female per year.

dispersal and density covary (that is, if dispersal distances are greater for owls that travel through unsuitable habitat), then the estimate of Ne would be exaggerated because, for

this species, our estimate of density is for an

area of farms and eastern deciduous woodland

(that is, generally good habitat).

An important point evident in table 8 is that

the results for the spotted owl do not stand out

or otherwise seem unreasonable compared with the

other five species. Additionally, with the exception of Bubo virginianus, the values of Ne

for these owls, including S. occidentalis , fall

in the same range as the values computed for an

assortment of passerine birds by Barrowclouqh

(1980). As pointed out by Barrowclouqh and

Shields (1984), such values are also in general

agreement with the results of karyoloqical and

electrophoretic analyses.

A final comment concerns the influence of kurtosis of the dispersal distribution and the

pair-to-pair variance in reproductive success on

the calculation of deme size. Neither of these

factors have previously been computed for analyses of Ne for birds. Shields (1981), for

example, suggests that correcting for kurtosis

of the dispersal distribution might result in a

significant reduction in the estimate of Ne.

This seems not to be the case for these owl

species: the size of the effect varies from 0 to

at most 25 percent. The reproductive variance

factor (FRS) is of greater importance, ranging

from about 0.6 to 1.2. No generalization seems

possible concerning this effect: its influence

may be to decrease, increase, or leave unchanged

an estimate of Ne derived in the absence of

data requisite for estimating the factor.

EFFECTS OF THE SPOTTED OwL MANAGEMENT PLAN

A major effect of managing‘ National Forest land

in the Pacific Northwest for timber harvesting

is a reduction of suitable foraging and nesting

habitat for the spotted owl. The object of the

spotted owl management plans developed by the

USDA Forest Service is to preserve a gridwork of

suitable habitat patches for the owls (SOMAS) in

the National Forests of California, Oregon, and

Washington. Although the precise details of the

overall SOMP are not clear, it appears that

about 800 to 1,000 SOMAs will be set aside for

pairs of spotted owls in the 3-State area. Unfortunately, a complete estimate of the effects

a SOMP will have on the genetics of spotted owls

would require a model of the population dynamics

of the owl/habitat patch interaction under the

plan. Because such a model is not available, we

must limit our analysis to the genetical effects

of the SOMP under unrealistic "best case" conditions, and can only outline an approach to the

analysis of actual future conditions.

Best Case. The best case, from a qenetical

point of view, would be a condition in which all

the SOMAs were used by breeding pairs; that is,

if occupancy were 100 percent. In reality, of

course, this is not possible as a long-term

equilibrium situation because individual owls

will eventually die and, depending on the nature

of age-structure and patterns of dispersal

through patchy habitat, it will take a finite

time for any patch to become reoccupied by a

breeding pair. Nevertheless, if the best case of

100 percent occupancy were realized, then there

would be about 850 pairs of owls spread over the

Pacific Northwest.

81
Table 8--Estimates of population genetics parameter& for selected species

of owls

Species σ ρ

(km) (km-2)

Tyto alba 31.14 0.08

Otus asio 44.03 0.30

- -

Bubobubo 32.78 0.01 - -

g. virginianus 216.35 0.15

Strix aluco 6.99 0.40

S.occidentalis 33.56 0.04 -

Nc F

K

F

RS Ne

974.85 0.93 0.86 0.87 678.33

7308.50 0.90 0.84 2

/ 0.78 4309.68

135.03 0.75 0.79 1.30 104.01

88229.72 0.96 1.17 0.67 66396.75

245.60 1.00 0.66 0.72 116.71

566.13 0.81 0.69 0.69 218.23

1

/ Root-mean-square dispersal distance (σ ), density (p), census number per

neighborhood (NC), correction factors for kurtosis (FK), variance in

reproductive success (

FRS), and generation time (FGT), and effective

population number per neighborhood (Ne).

2

/

 Mean for other 5 species (data for Otus asio not available).

At present, the data from California and Oregon

suggest that the density of owls in the Coast

Ranges and the Cascade Range is of the order of

0.03 to 0.04 owls per km2. This is an average

density over prime, fair, and unusable habitat.

A management plan with approximately 500 SOMAs

in Oregon plus Washington and about 400 in

California would translate into 1,800 adults in

approximately 110,000 km2 of equivalent area.

Thus, the overall density of the birds would

fall to 0.016 owls per km2. If life history

traits of the birds were unaltered by the patchy

habitat, then effective size would decrease correspondingly from the current value of about

220. In particular, we can estimate that Ne,

per local deme, would be reduced to:

4 π (0.016,(33.56)20.81(0.69)0.69 = 87.33.

Inbreeding at two levels must be considered in

determining the effects the best case scenario

of the management plan would have on the genetic

structure of the spotted owl. First, the effects

on the rate of loss of variation and increase of

inbreeding over the entire range must be found

and, second, the change in local inbreeding,

Fst,

caused by reduction in the effective size

of local neighborhoods must be computed. With

regard to the first problem, there is a question

of whether the entire population can be considered panmictic for purposes of calculating the

rate of increase of inbreeding. Unfortunately,

that problem appears not to be well studied

theoretically for realistic models. For example,

the generalization that a series of populations

can be considered panmictic if they ‘exchange one

or more individuals per generation is explicitly

based on an "island" model of population structure: it does not apply to more biologically

reasonable "stepping-stone" and "isolation-bydistance" models. Maruyama (1977) reports, however, that for a two-dimensional, continuous

space model the entire population can be considered panmictic if p σ

2

>l. For this case,

P σ

2 = 0.016(33.56)2

 is of the order of 20,

so the roughly 10 demes each of effective size

.i

$

85 can be considered a single panmictic population of size 850 for computation of loss of

variability. Expected overall inbreeding will

therefore increase at a rate of 1/2Ne, or

0.0006 per generation. (If the spotted owl

distribution is considered one-dimensional,

essentially the same result is obtained for the

"best case.")

In order to compute how Fst will change with a,-

the implementation of the management plan, we

compute the expected value, again using the

procedure of Wright (1969), for a series of 10

demes each of size 85. For such a case, Fst is

0.017. This, however, is not a per generation :*

increase of inbreeding of demes relative to the

entire population: it is the equilibrium level.

Wright (1969) indicated that the amount of time

required to achieve this equilibrium is of the

order of magnitude of the total number of neighborhoods in the population. Consequently,. local

correlation of genes within individuals is expected to rise from the current estimated level

of 0.007 to 0.016 over a period of about 10

generations.

Under the "best case" situation, the management

plan would result in an increase in local

inbreeding, relative to total variation, of

about 1 percent, and a slow loss of overall

variability, at a rate probably of the same

order as replenishment by mutation (Franklin

1980).

A GENERAL METHOD FOR ASSESSING

GENETIC EFFECTS OF A MANAGEMENT PLAN

The method outlined above should enable an interested researcher to compute the genetic effects of any particular management plan, given a

set of estimates of the key variables. The

particular calculations are for the unrealistic

case of 100 percent occupancy of the management

82
sites. A more realistic result could be obtained

s: if estimates of mean occupancy rate were available. An estimate of density based on the anticipated mean occupancy, if used in the above

equations, would yield an average value for the

-i

effective size of the managed population; from

this, estimates of inbreeding could be obtained

easily. Such an exercise ought to be performed

before any management plan is implemented.

A more sophisticated but more useful way of

realistically evaluating the genetic effects of

a management plan requires the development of a

model of the population dynamics of the species

including, especially, a model of death and

recolonization of the habitat patches or SOMAs.

Repeated simulation of such a stochastic model

would yield predictions of the time course of

effective deme size for the owl-habitat system.

From this a probability distribution of inbreeding rates could be obtained.

RECOMMENDATIONS

The statistics that have been recommended for

management purposes and discussed by Frankel and

Soulé (1981)--total effective population sizes

>r

of 50 individuals for short-term preservation,

500 for long-term, and a maximum of 1 percent

inbreeding per generation--must be regarded as

only guidelines. The models on which they are

based are quite simplistic. Nevertheless, they

5

must be taken as the most reasonable minimal

goal in the absence of more specific analysis of

the needs of any given species with its own population ecology, age structure, and social and

mating system.

Our analysis of the "best case' scenario for the

management plan for spotted owls outlines a

method for evaluating the effects of any management plan, given estimates of several important

parameters. Estimates of these are now critically needed, therefore we believe that it is

imperative to:

1. Devote research effort to investigating those

key aspects of the spotted owl's biology that

are relevant to the development of a model for

the dynamics of the owl's population.

2. Develop such a model and use it to investigate both the long-term stability of the owl's

population under various SOMPs and the probable

genetic effects of the SOMP.

3. Proceed with extreme caution in timber harvesting until the above results are obtained.

Our particular recommendations in regard to the

first item are:

1. To study the effects of patch size and habitat composition on occupancy and fecundity.

2. To study intensively the dispersal of juveniles to get information on whether (and with

what probability) isolated patches of suitable

habitat are found.

3. To estimate, by using surveys, the current

occupancy rates of isolated patches of good

habitat.

Additionally, more data on fecundity, adult and

juvenile survivorship, and dispersal are needed

to confirm or modify our preliminary estimates.

Finally, blood or tissue samples should be taken

from 20 to 25 juveniles at a couple geographical

locations during routine banding or radio-tagging activities for later electrophoresis. The

laboratory results could be used to assess current levels of inbreeding (Fis and Fst) and

genic heterozygosity of the species.

ACKNOWLEDGMENTS

A number of colleagues assisted us during the

course of this study. Eric Forsman, Gordon

Gould, and Rocky Gutiérrez generously provided

data from their own studies of spotted owls. In

addition, we thank Eric Forsman, Mark Shaffer,

J. L. David Smith, and Jared Verner for useful

conversations. Andrew Carey, Rocky Gutiérrez,

Charles Meslow, and Robert Zink offered helpful

comments on preliminary versions of the paper.

83
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d

84
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85
THE METAPOPULATION AND SPECIES CONSERVATION:

THE SPECIAL CASE OF THE NORTHERN SPOTTED OWL

Mark L. Shaffer

INTRODUCTION

ABSTRACT: The conservation of patchily distributed species presents a complex

problem for land-use planning and wildlife management. A new paradigm of population structure will be necessary to understand the extinction-persistence

dynamics of such species both for site-specific and regional conservation

efforts. The metapopulation model provides a beginning conceptual framework

for solving this problem.

The model is reviewed in light of the problem of avoiding stochastic extinctions

and illustrated with the current problem of conserving the northern spotted

owl (Strix occidentalis caurina) in the Pacific Northwest. Major theoretical

and empirical research needs are identified both for the applicability of the

metapopulation model in general and for the northern spotted owl in particular.

The equilibrium theory of island biogeography

(MacArthur and Wilson 1967) has had a significant

impact on biogeography, population ecology, community ecology and conservation. Currently, controversy persists on the validity of the theory

(Gilbert 1980, Simberloff 1983) and the applicability of principles derived from the theory for the

design of nature reserves (Margules and others

1982, Simberloff 1983). Irrespective of the outcome of these controversies, the theory, and the

studies it has spawned, have led to three realizations of fundamental and continuing importance

to conservation:

1 . Local extinctions and colonizations, in ecological time, may be common events.

2. Extinctions and colonizations may, in many

cases, be the products of stochastic events.

Mark L. Shaffer is a nongame staff specialist for

the Office of Migratory Bird Management, U.S. Fish

and Wildlife Service, Washington, D.C.

3. The simple geometric variables of habitat

area and interhabitat distance, through their

relationship with stochastic events, may be

important determinants of the rate of local

extinctions and colonizations.

These realizations raise key issues that must.

be addressed if certain conservation efforts

are to be successful. The importance of these

realizations does not hinge on the validity of

any particular theory of the interplay of the

extinction and colonization processes. The

fact that equilibrium theory remains inadequately validated as a general description of

nature simply means that the relationship of the

extinction and colonization processes remains

unclear, particularly their relative frequencies

and subsequent balance for various scales of

time, size, and population structure. In fact,

some of the studies necessary for conservationists

to deal effectively with the issues raised by

these realizations will help in further vali-- 'P

dating, refuting, or refining equilibrium theory. -

To date, most efforts to apply equilibrium theory

to conservation have involved postulating principles on the size, configuration, and dispersion d

of nature reserves that will maximize the species

86
richness they contain and minimize the loss of

species over time (for a review, see Margules and

others 1982). An equally challenging problem is

that of assessing the probabilities of persistence

for species that are patchily distributed and

whose patchwork of habitat is undergoing alteration.

An example is an old-growth-dependent species in a

National Forest where the natural successional

mosaic is undergoing alteration due to both natural

disturbance and resource management activities such

as timber harvest. Here the question is how the

probability-of species persistence on the forest

responds to various regimes of patchwork alteration (that is, reduction in either the number or

size of habitat patches and their increased

isolation, or both). Managers need to know how

many old-growth stands of what size and what distance from similar neighbors must be maintained to

assure the persistence of the species in the

forest to meet some acceptable management criterion

(for example, 95 percent probability of persistence on the forest for one successional or

rotational cycle). The solution to this complex

problem relies on various areas of biological and

ecological knowledge that are not yet fully

developed theoretically, empirically, or experimentally. These areas include stochastic population dynamics and the roles of temporal and

spatial environmental heterogeneity, dispersal,

and-genetic diversity in population regulation and,

hence, persistence. The tone of this paper is,

therefore, necessarily speculative. My goal is

to establish a frame of reference, identify key

processes and variables, and point to potentially

fruitful approaches for further work in this

important area. My specific objectives are;

1. Reiterate the probabilistic component of

extinction and, hence, conservation.

2. Introduce conservationists to the concept of

the metapopulation as a basic frame of reference

for conserving patchily distributed species.

3. Review a simple model of metapopulation dynamics.

4. Outline the potential relationships of the

factors affecting metapopulation extinction dynamics

to the spatial configuration of habitat.

5. Examine the implications of these relationships

for conservation of the northern spotte owl (Strix

occidentalis caurina) in terms of both management

options and research needs.

THE STOCHASTIC COMPONENT OF EXTINCTION

Populations may go extinct from a variety of factors,

but almost any factor can operate in two very

different ways. Systematic pressures, despite

temporal or geographic variation, show a significant trend over time that negatively impacts the

population. Long-term climatic changes are one

example. In such a situation, the size of the

population bears only on the length of time the

population persists, but extinction is a foregone

conclusion provided the trend does not change.

Stochastic perturbations show no significant

trends with time but still may force a population

to extinction if sufficiently frequent or severe.

Drastic, intermittent variations in climate are

an example of this mode of extinction. In this

case, the population's size and distribution may

be critical determinants of its persistence

through the temporary period of unfavorable conditions.

Once systematic pressures have been identified

and solutions instituted for a species in

jeopardy , the question of stocahstic perturbations remains. One essential goal for effective

conservation is the minimization of extinctions

due to stochastic perturbations. The northern

spotted owl provides an example of the relationship of these two modes of extinction. The

species is currently of concern because of its

apparent dependence on old-growth coniferous

forests (Forsman and others 1984, Gutiérrez and

others 1983), a habitat which has steadily declined

over the years due principally to timber harvest.

Further habitat declines are anticipated due to

the high economic value of the timber that provides suitable habitat. Determining that habitat

preservation is critical to the species survival

is the answer to the systematic pressure threatening this species. But determining how much

habitat to preserve and how it is distributed

must address the species' viability in the face

of the stochastic perturbations to which it may

be subject. Land is a precious resource. So is

biotic diversity. When the conservation of a

species conflicts with alternative land uses, the

first question to arise is what is the minimum

land area necessary to achieve conservation.

Given that localized extinctions are, in part,

the results of stochastic events, and the probability of such extinctions increases with time

and decreasing population size, determining the

amount of land necessary to achieve the conservation of a species must address three key issues:

1. The types of stochastic perturbations to be

anticipated.

2. The time frame to use in conservation planning.

3. The degree of security sought for the unit

being conserved.

These issues are addressed for a single, isolated

population in an earlier paper (Shaffer 1981).

The northern spotted owl represents a different

problem--a species distributed on a patchwork of

habitat. A new perspective on population structure

is necessary to deal with the conservation of such

species.

THE METAPOPULATION

The Metapopulation Concept

Most species are patchily distributed and can be

viewed as a population of populations (Levins 1970)

or a metapopulation (Wilson 1975). Wilson (1975)

provides a metaphorical description of the metapopulation as ".. . .a nexus of patches, each patch

winking into life as a population colonizes it and

winking out again as extinction occurs. At equi87
librium the rate of winking and the number of

occupied sites are constant, despite the fact that

the pattern of occupancy is constantly shifting"

(fig. 1). For such a patchily distributed species,

global extinction is equivalent to its extinction

on all patches. Effective conservation of such

species thus requires an understanding of the

processes of local extinction and colonization

and the factors affecting these processes.

Levins' Model

Levins (1970) provides an initial treatment of

metapopulation dynamics (table 1). His model

considers three parameters: the proportion of

patches occupied by populations at some particular

time (Nx), the proportion receiving immigrants

(prospective colonizers) in an instant of time

(m) , and the proportion of patches whose populations are going extinct in an instant of time

(e). The model states that the Change in

occupancy of patches over time is a function of

the rates of immigration and extinction.

Levin's model, although a general one, is oversimplified. It is formulated in continuous time.

It assumes either equal size patches or no relationship between patch size, population size and extinction probabilities. Nevertheless, the model provides a conceptual beginning for a more detailed

consideration of the determinants of metapopulation persistence.

Table 1--Levins (1970) model of metapopulation

dynamics

Let:

(t) = proportion of patches occupied by populations at time

m = proportion of patches receiving migrants in

an instant of time (whether occupied or not).

e = proportion of populations becoming extinct in

an instant of time.

Then:

dNx/dt=mNx(l-Nx)-eN (1)

X

and, at equilibrium:

Nx=l-e/m (2)

k

E

88
Levins' (1970) analysis of this model reveals 

several important findings. First, for the metapopulation to persist, the proportion of patches 

receiving immigrants (or the rate of immigration, 

m) must exceed the rate of extinction (e). If the 

equilibrium proportion of occupied patches (fi ) is 

close to 1, a change in extinction rate has r%atively listle effect on fi . If i is small, 

however, N is more sensi%ve to shanges in 

extinctionx rate. When extinction rate shows 

random variation through time the immigration rate 

must exceed the extinction rate by more than the 

variance of the extinction rate for the 

to persist (that is, m-z > 0 2). 

species 

If the variation 

in extinction rate is autoco&elated, the persistence of the metapopulation is further reduced. 

If the immigration rate (m) is large, then the 

persistence of the metapopulation is very sensitive 

to changes in m. Different species are likely to 

have different distributions of immigration 

probabilities (compare passive, wind-dispersed 

seeds to actively dispersing birds). Levins (1970) 

and MacArthur and Wilson (1967) argue that an 

exponential decline of dispersing individuals with 

distance is a reasonable qualitative description 

for passive dispersing species. In this case, a 

change that doubles the distance between patches 

will square the immigration rate and will have a 

greater effect on the chances of persistence than 

would doubling the extinction rate. Consequently, 

increased patch separation, as this affects dispersal probabilities, may be the limiting factor 

in determining metapopulation persistence for 

passively dispersing species. Though based on a 

simplistic model, this is an important finding 

as, in Levins' words, it: 

. . .forces us to change our notion of 

suitable habitat. If there is always 

a finite probability of extinction of 

a local population even in the best of 

circumstances, a region will be suitable 

or unsuitable depending on the density 

of appropriate sites and a species will 

fail to survive even if its optimal 

hahitat is present. 

Thus, habitat (patch) density may be as fundamental to conservation as habitat quality and 

management actions that reduce habitat density 

may lead to the regional extinction of a species 

even if habitat of suitable quality remains. An 

important management corollary of this result is 

that effective conservation of patchily distributed species may require the preservation of 

suitable but intermittently, perhaps currently, 

unoccupied habitat. 

The minimal objective of metapopulation conservation is simply its-continued existence; that is, 

persistence in one or more patches fiV > 0). Thi.s 

I 

requires maintaining an immigration rZte greater 

than the extinction rate (m > El. This can be 

achieved either by increasing the immigration rate 

or decreasing the extinction rate. Aside from the 

foregoing consideration of the effects of interpatch distance on immigration, Levins' model does 

not explicitly incorporate the spatial dimensionality of the metapopulation in terms of patch 

number or size and their effects on immigration 

or extinction rates. Yet, if population size 

correlates with area, probability theory would 

indicate that' patch number is an important consideration for both immigration and extinction 

rates; and both probability theory and empirical 

studies (Gilpin and Diamond 1981, Jones and 

Diamond 1976, Simberloff.1976) indicate that patch 

size should be an important determinant of 

extinction rate. To go further requires incorporation of this spatial dimensionality and an 

examination of its effects on metapopulation persistence. First, it is necessary to more clearly 

define the specific objectives of metapopulation 

conservation. 

Metapopulation Structure and Conservation Objectives 

From a conservation standpoint, the interest is in 

estimating certain probabilities of the extinctionpersistence of the metapopulation or parts thereof. 

These probabilities may be defined as shown in 

table 2 for a metapopulation starting from saturation (that is, all patches occupied). 

Table 2--Definitions and relationships of metapopulation probabilities 

Let: 

e. = 2 probability of extinction on patch i; 

Pi = probability of persistence on patch i; 

B = probability of extinction everywhere (that 

is, all patches); 

P = probability of persistence everywhere; 

e 

i%, 

= probability of extinction somewhere (that 

2 1 patch); 

pz = probability of persistence somewhere. 

Then: 

e. = l-p. 

p', = 1-e; 

E=fe. 

C-1 z 

iv P=q 

G-1 

e 

X 

= 1-p = l= $f p. 

f=l 2 

p, = 1-E = I- i! e. 

{cl z 

If the metapopulation under consideration is a 

closed system (that is, it is not connected to or 

embedded in another metapopulation) and patches 

are fixed, permanent, and independent with regard 

to stochastic events, then these extinctionpersistence probabilities may be calculated as 

shown in table 2. For conservation purposes 

interest is most likely to be in determining the 

89 
probabilities of (1) extinction in certain patches 

(e.i, (2) over all patches (E), or (3) of persiste&ce of the species somewhere within the patchwork (pxJ X 21). 

Clearly, once the site-specific extinction 

probabilities (e. 's) are estimated all other 

probabilities cak be calculated. Equally clear 

is that we generally do not know, nor can we 

expect to estimate, site-specific extinction 

probabilities over a short time with much meaning 

for long-term planning (but see Gilpin and Diamond 

1981). Moreover, estimating site-specific extinction probabilities for an existing metapopulation 

configuration does not necessarily allow prediction 

of the e. schedule that will pertain to a new 

metapopu 'I ation configuration, because this value 

is, in part, a function of the configuration in 

which it is estimated. Even on a qualitative 

basis these relationships raise an important 

management issue: the specific objective of 

metapopulation conservation. Is the objective to 

assure the persistence of the species: 

1. On a particular patch.or set of patches 

(minimize e 2 and/or e2, etc.)? 

2. On all patches (minimize ei's and E)? 

3. On at least one or some preselected percentage 

of unspecified patches (maximize p,, x Al)? 

In the absence of an answer to this question, no 

definition of a minimum patchwork can be offered. 

The answer chosen may make a difference in whi.ch 

land-use pattern(s) will be acceptable. 

In the remainder of this paper, the focus will be 

on minimization of site-specific (e.) and overall 

CEI extinction probabilities as the'conservation 

objective probabiliti 

choice. E s. This is an arbitrary 

Because E =.n e. anything reducing sitespecific extinction $Tiba%ilities will automatically 

reduce overall extinction probabilities, but the 

chances of overall extinction may be reduced simply 

by increasing patch number in). Though considering 

both site-specific and overall extinction probabilities may introduce a certain redundancy, the 

factors affecting these probabilities can operate 

at different levels of metapopulation structure. 

The discussion will be more comprehensive if botb 

types of probabilities are included. It should 

also be useful to contrast site-specific conservation vexsus patchwork conservation. 

It should be noted that because px=I-E, minimizing 

the overall extinction probability automatically 

maximizes the probability of persistence somewhere, 

which will usually be the real objective of metapopulation conservation. 

METAPOPDLATION CONFIGURATION AND STOCHASTIC 

EXTINCTION DYNAMICS 

There are four categories of stochastic perturbations that may be factors in the extinction of 

a population (Shaffer 1981): 

1. Demographic stochasticity caused by chance 

events in the survival and reproduction of a finite 

number of individuals. 

2. Environmental stochasticity resulting from 

temporal variation of habitat and niche parameters 

such as weather, food.supply, predators, etc. 

3. Natural catastrophes such as floods, fires, 

hurricanes, etc. 

4. Genetic stochasticity, or changes in gene 

frequencies with negative effects on demographic 

parameters resulting from founder effect, random 

fixation, or inbreeding. 

It is reasonable to reduce this organization to 

three categories by recognizing natural catastrophes as merely an extreme form of environmental 

stochasticity. One important distinction within 

this new composite categorization.is that of 

stochastic events that are contagious by nature 

(for example, epizootics). It is anticipated 

that such events may have spatial dynamics that 

differ from noncontagious events such as floods, 

drought, etc. Ruediger (1985) presents examples 

of these phenomena relevant to the northern 

spotted owl. 

All these categories of stochastic perturbations 

increase in importance with decreasing population 

size. Moreover, they are likely to interact, as 

for example an environmental perturbation that 

reduces population size over time to the point 

where inbreeding depression may become a factor 

by negatively impacting the demographic parameters 

of survival and fecundity. Though increased 

attention has recently been focused on the 

importance of genetic stochasticity (Frankel and 

Soul6 1981, Schoenwald-Cox, and others 1983, Soul6 

and Wilcox 1980), there is still no theoretical 

or empirical guidance on which category of 

stochastic perturbation sets the lower limit to 

population viability. This may well vary from 

one type of population to another (for example, 

density-independent populations with nonoverlapping 

generations vs. density-dependent populations with 

age structure). 

To better understand how the geometric distribution 

of habitat may affect metapopulation extinction 

dynamics, it is necessary to consider how changes 

in the metapopulation configuration variables 

(that is, patch number, size, and isolation) may 

affect the objective probabilities (e., E) caused 

by the various categories of stochasttc perturbations (demographic, environmental, genetic). 

Because habitat management chiefly controls the 

metapopulation configuration variables, this 

discussion is organized with each variable considered separately. The discussion is condensed 

in table 3 where, for a particular change in 

each configuration variable, the expected change 

in site-.specific and overall extinction probabilities caused by various stochastic perturbations, 

acting through various conditions, is given. 

This dicuasion assumes a strong, positive correlation between habitat area and population size. 

90 
Table 3--Expected changes in site-specific (e.) and overall (El extinction probabilities with changes in 

metapopulation configuration variables causedzby various types of stochastic perturbations. 

Metapopulation 

configuration Objective 

variable Change probability Change Caused by Acting through 

Patch # 4 e. 2 

E 

4 demographic stochastic-&y sources of immigrants 

4 noncontagious stochastic events sources of immigrants 

44 contagious stochastic events sites for initiation, 

sources of immigrants 

4 genetic stochasticity sources of immigrants 

44 demographic stochasticity number of realizations, 

sources of immigrants 

44 noncontagious stochastic events environmental correlation, 

sources of immigrants 

4-t contagious stochastic events sites for initiation, 

sources of immigrants 

++ genetic stochasticity number of realizations, 

sources of immigrants 

Patch Size 4 e. 2 

E 

44 demographic stochasticity 

4.4. noncontatious stochastic events 

44 contagious stochastic events 

s+ genetic stochasticity inherent resilience, 

number of immigrants 

s+ demographic stochasticity 

++ noncontagious stochastic events 

$4 contagious stochastic events 

44 genetic stochasticity 

Isolation 4 e. 2 4 demographic stochasticity 

4 noncontagious stochastic events 

44 contagious stochastic events 

E 

4 genetic stochasticity 

4 demographic stochasticity 

4+ noncontagious stochastic events 

Sf contagious stochastic events 

4 genetic stochasticity 

distance for immigrants 

distance for immigrants 

distance for infectives, 

distance for immigrants 

distance for immigrants 

distance for immigrants 

distance for immigrants, 

environmental correlation 

distance for infectives, 

distance for immigrants 

distance for immigrants 

Further. the entire discussion is intuitive and is 

based on common sense expectations. Unless otherwise stated, all cause-effect statements come with 

the caveat of, "all else being equal." This is 

not intended as a comprehensive, exhaustive discussion, but rather as an indication of the major 

relationships and potential complexity of the 

interplay between various stochastic perturbations 

and metapopulation configurations. 

Patch Number 

Increasing the number of patches should decrease 

both site-specific (ei) and overall (E) extinction 

probabilities for two reasons. First, e. should 

be reduced because more patches constitute more 

sources of immigrants that may bolster a patch 

population temporarily failing because of demographic, environmental, or genetic stochasticity. 

This is the so-called “rescue effect" (Brown and 

Kodric-Brown 1977). This phenomenon deserves 

much more theorectical and empirical attention. 

91 

Second, because the overall extinction probability 

is equal to the product of al& site-specific 

extinction probabilities (E=.a e.; if e.'s are 

independent), the chances of%erkl ex&ction 

can be reduced simply by adding to patch number 

even if the site-specific extinction probabilities 

remain unchanged. The larger site-specific 

extinction probabilities are, however, the more 

patches must be added to achieve a certain 

specified overall extinction probability. For 

example, if ei=e2=e5, etc., and the objective is 

to achieve E 0.70, then for e.=O.S, N must 

be > 4. If eT=0.9, however, N kust be $ 22 to 

achyeve the s:ecified level of E. The T;ey point 

here is the extent to which patches are independent with respect to the stochastic perturbations 

affecting populations. The greater this independence, the greater the benefit of adding additional 

patches. If patches are not independent with 

regard to environmental or genetic stochasticity, 

then adding additional patches is equivalent to 

simply adding the individuals they-contain to an 

aggregate population size. That is, the meta- 
population behaves as one unsubdivided population.

This pattern is potentially very complex as the

degree of correlation between patches may well vary

from one type of environmental perturbation to

another.

The one potential negative aspect of increasing

patch number concerns contagious stochastic events.

For example, consider forest fires as a form of

contagious environmental stochasticity. The more

patches there are, the more likely at least one

will be affected by a forest fire during any

particular time period (if patch number adds area)

The larger the number of sites for initiation of a

contagious disturbance, the more likely that any

particular patch may be disturbed given that the

degree of isolation-does not change. How important

a consideration this may be is, of course, unknown

and is likely to be quite variable for species

and from one habitat to another.

Patch Size

Because all forms of stochastic perturbations

decrease in importance with increasing populationsize, increasing patch size should significantly

reduce both site-specific and overall extinction

probabilities. An important question is the form

of the functional relationship between population

size and e.. Several theoretical models (MacArthur

and Wilson'1967, Richter-Dyn and Goel 1972, Wright

and Hubbell 1983) have demonstrated that, considering

demographic stochasticity alone, the expected time

to extinction in relation to population size for

an isolated population takes the general form of

an exponentially increasing function (fig. 2a).

That is, starting from a population of one, the

expected time to extinction increases so rapidly

with an increase in population size (here expressed

as K) that, in the case of Richter-Dyn and Goel's

model, by the time K=20 (individuals) the population

is essentially immortal with respect to any time

period of potential interest to managers. This

relationship is very sensitive to changes in r,

the intrinsic rate of increase. Extreme caution

should be used in interpreting the results of these

models because they do not incorporate the effects

of age-structure or environmental or genetic

stochasticity. Shaffer and Samson (in press) show

that incorporating age structure and environmental

stochasticity drastically reduces the predicted

population viability obtained. from Richter-Dyn and

Goel's model. More importantly, it must be

remembered that the expectation of extinction even

in a viable environment approaches one as time

approaches infinity. Larger population size merely

makes this approach more gradual (fig. 2b). Further,

incorporating genetic stochasticity would likely

have an equally significant effect, at least to

some species. Thus, the whole class of models

dealing with only demographic stochasticity becomes

suspect for application to real world problems.

From a genetic standpoint, Franklin (1980) has

argued that a minimum effective (in the genetic

sense) population of at least 50 breeding adults

is necessary to avoid the short-term deleterious

consequences of inbreeding and that an effective

population size of 500 may be necessary for longterm genetic adaptability. This argument suffers

DEMOGRAPHIC

3

ENVIRONMENTAL

many of the shortcomings found in the demographic

models cited above. It does not include the effect

of age-structure or environmental stochasticity.

In fact, there do not seem to be any comprehensive

theoretical models that integrate the various

categories of stochastic perturbations. This is a

crucial need for management and may prove an enlightening exercise for basic ecological theory.

Different species are likely to show different

sensitivities to the various types of perturbations. For example, Karr (1982) presents evidence

that, amongst forest birds in tropical undergrowth,

the variability in population size is a better

predictor of extinction than population size itself.

Karr interprets the coefficient of variation (CV)

in population size as a first approximation of

environmental variability. This result applies

only to a subset of species sufficiently abundant ?-

to be considered immune to extinction from demographic stochasticity alone. This would seem to

indicate that demographic stochasticity sets the

lower limit on species survival but that environ- &

mental stochasticity is the most important factor

above this lower limit.

92
Ehrlich (1983), based on his work with Bay checkerspot butterfly populations (Euphydryas editha

bayensis), believes most local extinctions in this

species are the result of catastropic weather events

and the effects on host food plants rather than

"normal" variation in weather patterns.

Rails and Ballou (1983) present evidence that, for

zoo populations of mammals, inbreeding depression

has had a significant deleterious effect on

demographic viability and suggest similar effects

may occur in wild populations that become much

reduced.

This is by no means a comprehensive review, but

work with three different major taxonomic groups

(birds, butterflies, mammals) has yielded three

different indications of- which type of stochastic

perturbation may be most important in determining

population viability. This area is rife with

potential for theoretical, empirical, and experimental work.

Patch Isolation

The distance between patches is important because

of its potential effects on the probability-of

interpatch movements and, thus, the operation of

the rescue effect, the frequency of recolonizations,

and the rate of immigration in maintaining a species'

genetic variability, and the avoidance of inbreeding.

Reduced isolation is a two-edged sword because,

though it may produce the benefits mentioned above,

it may also entail a high degree of inter-patch

correlation with regard to noncontagious environmental stochasticity and the facilitation- of the

spread of contagious environmental events. The

relative importance of this mixed blessing is, of

course, unknown and, again, likely variable.

Several efforts at modelling the importance of

dispersal to population regulation and persistence

(Roff 1974a, 1974b, 1975; Vance 1984) have produced

some interesting results. Roff (1974a) demonstrates

that, for populations with a stochastic exponential

growth rate, increasing environmental stochasticity

greatly reduces the probability of population persistence. If such a population is subdivided and

there is movement of individuals between patches,

persistence of this metapopulation configuration

may be increased several orders of magnitude over

the original undivided configuration.

Vance (1984), examining a number of population models,

shows that, for a wide variety of dispersal patterns,

dispersal tends to stabilize population fluctuations.

In some circumstances, however, dispersal does not

increase population stability. He further argues

that the details of patch location do not alter

the qualitative stabilizing effect of dispersal.

But the scenario of his spatial argument (that is,

equispaced patches all connected or all isolated)

is too simplistic to be of interest for application.

The value of Roff's models, beyond their obviously

important heuristic value, is limited by their

consideration only of exponential growth. Vance's

results are much more robust but suffer from an

inadequate consideration of spatial effects.

Moreover, neither model incorporates the negative

and potentially destabilizing aspects of dispersal,

namely the effects of contagious stochastic events.

As with the relationship of population size and

extinction, assessing the effects of metapopulation

configuration on persistence awaits the development of comprehensive, realistic models characterizing various life-history types.

The Trade-offs of Size, Number, and Distance

An examination of table 3 and the foregoing discussion summarize an intuitive expectation that

many, large patches, which are close together,

will usually minimize site-specific and overall

extinction probabilities. Any conservation effort

will necessarily be limited to some fixed amount

of habitat and the question immediately arises of

how best to distribute the habitat available.

If total habitat area is fixed then an increase in

average patch size must correspond to a decrease

in patch number. If the regional boundaries of

the metapopulation are fixed then an increase in

patch number may correspond to a decrease in patch

isolation. If area and regional boundaries are

fixed then an increase in patch size must correspond to a decrease in patch number and may entail

an increase in isolation.

A small number of patches may be compensated for

by large size and reduced isolation. Small patch

size may be compensated for by increased patch

number and decreased isolation. Increased isolation may be mitigated by increased patch number

and increased patch size. Which strategy, or what

mix of strategies, to use in any particular

circumstance will depend on the particulars of that

situation and the functional form of the relationships between the objective probabilities and

metapopulation configuration variables, Without

comprehensive models of the relationship of population size and configuration to extinction

probabilities under the effects of all sources of

stochastic perturbations, rational decisions on

acceptable metapopulation configurations will not

be possible. Even without such models, however,

some preliminary guidance may be obtained from

table 3. First, whether the objective is to

minimize site-specific or overall extinction, increasing patch size should uniformly reduce the

chances of extinction to all sources of stochastic

perturbations. Neither patch number nor isolation

is expected to have such an unambiguous effect on

site-specific or overall extinction. This agrees

with the results of Roff's (1974b) theoretical

simulation models.

Second, additional patches should reduce both ei's

and E but should have a more dramatic effect on

the latter, contingent upon the degree of independence of the patches with regard to stochastic

environmental perturbations. The hazards of

increased patch number enhancing the probability

of extinction caused by contagious stochastic

events is unknown but probably minor.

Third, because isolation will often correlate

inversely with the environmental independence of

93
patches but correlates directly with the ease of

transmission of contagious stochastic events, lack

of isolation is not an unambiguous blessing. A

better knowledge of the prevalence and importance

of the rescue effect and recolonizations relative

to these potential disadvantages is necessary to

better assess isolation's likely importance for

minimizing site-specific and overall extinction.

If the benefits of proximity outweigh the risks,

then there is likely some tradeoff of distance

with size, such that one configuration (A) of a

certain patch size (x) and interpatch distance (y)

behaves (that is, has the same persistence/extinction

schedules) as another configuration (A’) of smaller

patches (x') closer together (y') (fig. 3).

Determining the existence and form of such a tradeoff should be of great importance in maximizing

management options for land-use planning.

A’

Figure 3

scale).

.--The tradeoff of size and distance x' = x/2 y' = y/2 (not to

If there is a linear relstionship of the effects of size

and distance on extinction probabilities, site-specific and overall extinction probabilities should be equal in these two configurations.

What all of this means is-that extinction/persistence

probabilities are the result of the interplay of

numerous forces, some opposing, that are determined,

at least in part, by the configuration of the

habitat patchwork. Thus, there is likely no simple

prescription for patchwork configuration that will

universally maximize persistence or minimize extinction probabilities. It also means that-the objective of metapopulation conservation must be explicit $

because the effects of various alterations may have

differing effects on differing extinction/persistence

probabilities. In other words, what's best to

reduce the overall extinction probability (E) may

not be best to reduce site-specific extinction .i

probability (ei). For example, to minimize e for

a given i, may require one very large patch, but

minimizing E may require numerous, smaller patches

of intermediate isolation.

A crucial corollary of the tradeoff of size and

distance, involves the twin dangers of metapopulation restriction and diffusion (fig. 4). In

most scenarios conservationists will have to

accept less than all of the remaining habitat for

a species of concern. One goal of conservation

is to maintain the representative distribution of

a species. Yet specialized management can be administratively burdensome. The dilemma may then

be one of choosing a dispersion-pattern either to

maximize the species' geographical representation

or to minimize the administrative burden. These

may be opposing goals. Minimizing administrative

burdens may require dedicating a number of patches

close together and not having to deal with the

species elsewhere. Geographic representation may

require that patches be widely dispersed. The

closer patches are, the more likely they are to

behave as one. Thus, the potential to lose the *+:

species increases due to a contagious stochastic

event or the fact patches are-so close (for example,

all in one watershed) that they are essentially

one with regard to environmental perturbations.

This is the danger of restriction. On the other 02

hand, maximizing dispersion may lead to a patchwork whose interpatch distances are so great that

each patch behaves as an isolate (that is, dispersing individuals cannot reach another patch),

and there is no realized benefit in terms of the

rescue effect, recolonization, or gene flow. This

is the danger of diffusion.

Clearly, this "stew" of processes, variables, and

probabilities would be rendered more meaningful,

if:

1. Data were available to derive the functional

relationship of the objective probabilities to the

various processes as these change with the various

metapopulation configuration variables.

2. Theoretical models integrating the four types

of stochastic events were available for both a

single population and a metapopulation configuration

for a variety of life-history types.

It would seem that realistic; theoretical models, r

be they analytical or numerical, could aid in

determining the sensitivity of metapopulation persistence to various changes in metapopulation configurations. In table 3 I've indicated a postulated .

qualitative effect with a directional arrow. A .g

next level of understanding would be to know which

arrows are large and which small. Theoretical

models may provide this. Eventually arrows could

94
be replaced with equations but this will require

extensive empirical and experimental work.

THE SPECIAL CASE OF THE NORTHERN SPOTTED OWL

How does the foregoing discussion relate to the

current problem of conserving the northern spotted

owl in public forest lands in the Pacific Northwest? From the reports on current research and

management programs, much important data are being

gathered on this species, particularly with regard

to dispersal and the survivorship of young. In

addition, research to date (Forsman and others 1984,

Gutiérrez and others 1983) has shown the species'

preference for mature and old-growth timber for

foraging, roosting, and nesting; revealed a large

home range size; demonstrated the varialbe success

1 of the species' reproductive performance; and

provided some estimate of overall population size

and distribution. All this information is necessary,

but it is not yet sufficient for comprehensive

2 conservation planning. Still lacking are sex- and

age-specific mortality and fecundity rates; sex and

age structure (which may be derived from the

preceding); some measure of the variability of

these rates from year to year, and data on the

genetic and breeding structure of the species.

Thus, there are insufficient data with which to

construct a comprehensive quantitative population

model.

In the absence-of sufficient data to develop cornprehensive quantitative approaches to assessing -

the viability of various spotted owl habitat configurations, two management approaches have

emerged. The first is what might be termed a

qualitative approach; using available information

on population size, distribution, habitat preference, home range size, and an intuitive appreciation

of the importance of dispersal, to develop guidelines for management (Oregon Interagency Spotted

Owl Management Plan). The other approach incorporates the above but is based on the growing use

of genetic arguments to assess minimum viable

population sizes (Salwasser and others in press).

With regard to the former approach, its chief

weaknesses are the need for a better-understanding

of how home range size and the relative composition

of mature and old-growth (that is percent composition - a rough measure of habitat quality) impinges on reproductive success, adult survivorship,

and their variability; and the apparently arbitrary

choice of distances between spotted owl management

areas (SOMAs). Current work on dispersal should

help correct the latter weakness fairly quickly,

while extensive studies of reproductive success

across a gradient of home range size and percent

composition can partially alleviate the first weakness. For the temporal component of variation in

SOMA suitability by size and percent composition

there is simply no substitute for long-term

monitoring. Certainly, using minimum-sized home

ranges for long-term management guidelines would

be courting failure as would a spacing regime for

SOMAs based on maximum dispersal abilities. Combining these hazards with a dedication of a minimum

number of SOMAs of low quality would further

reduce the species survival probabilities.

The genetic approach represents a conceptual advancement based on both theoretical and empirical

knowledge. However, several cautionary notes need

to be sounded. First the 50/500 rule (Franklin

1980, Soulé 1980) discussed earlier, which seems

to be emerging as a standard of application, is

based on the simplest of analytical population

genetics models, which do not take into account

either age-structure or environmental stochasticity.

Based on previous work on modelling grizzly bear

(Ursus arctos) populations, the inclusion of age

structure can dramatically affect the results of

projecting population survivorship based on demographic stochasticity alone (Shaffer 1978). To

the extent that genetic diversity directly affects

demographic parameters (for example, mortality,

fecundity), and this is the heart of the inbreeding

depression argument, the inclusion of age-structure

in determining effective population sizes may

dramatically increase estimates of minimum viable

population sizes. Make no mistake, there is no

doubt that inbreeding depression poses a grave

risk to small, isolated populations. What remains

in doubt is what constitutes small for organisms of

varying genetic structure and life-history patterns.

95
In this regard, Barrowclough and Coats (1985)

estimate that the likely effective population size

(in the genetic sense) for this species would

approximate 2.1 of the census population size. This

means that to achieve the goal of long-term adaptability (500 breeding adults, Franklin 1980) may

require a census population goal of 1050 breeding

adults or 525 pairs. This is very close to the

current management objective of 500 pairs for

Washington and Oregon (Salwasser and others in

press).

A second point reiterates what emerged from the

preceding consideration of metapopulation extinction

dynamics. There currently exists no integrated

theoretical model providing guidance on which class

of stochastic events sets the lower limit to population viability. Implicit in the assumption of

the 50/500 rule is that, if these sizes are

sufficient to overcome the dangers of drift and

inbreeding depression, all is well. This remains

to be demonstrated. In fact, for density independent populations occupying variable environments,

environmental stochasticity may be the limiting

factor for population persistence, as appears to

be the case in certain checkerspot butterfly populations (Ehrlich and others 1980). On the other

hand, for large-bodied, long-lived, adaptable

species with low genetic variability and some

tolerance to inbreeding, demographic stochasticity

may be the key factor in determining population

persistence. How much demographic considerations

or environmental conditions would modify the current

management objective for the northern spotted owl

is unknown, but it is highly probable an increase

in the objective would be required.

MANAGEMENT OPTIONS AND RESEARCH NEEDS

It is clear from the discussion in the section,

"Metapopulation Configuration and Stochastic

Extinction Dynamics," that projecting the

survivability of various metapopulation configurations is a daunting task. It is safe to say

there are insufficient time and resources available

to determine, empirically, all the requisite data

over a sufficient period to ensure developing an

accurate predictive capability for projecting

population persistence of the spotted owl. This is

a general and fundamental problem in conservation

biology today; being asked to determine the longterm viability of wildlife species based on shortterm studies. Nevertheless, the issue must be

addressed. A reasonable strategy involves three

components:. (1) theoretical research, (2) shortterm empirical studies and (3) integration of a

long-term monitoring-research program with current

management action (Salwasser and others in press).

Theoretical Research

As discussed above, theoretical ecology lacks the

detailed models necessary to provide sound guidance

on the interplay of the factors affecting stochastic

extinctions for populations of different life

history patterns. It seems reasonable that the

management agencies in need of such guidance should

seriously consider instituting a program of basic

research to address this weakness. In my judgment

a few representative simulation models of various

major life hisotry types would go a long way

toward providing at least sound qualitative

guidance on the likely persistence of various

populations in relation to various stochastic

factors and various land-use patterns. Such k-_

generalized models would also be useful in

generating hypotheses for empirical field or experimental laboratory studies. There can only be

a growing need for such guidance in the future. 1

We may as well start now. In this regard it is

very encouraging to learn of efforts by the USDA

Forest Service to develop an interactive computer

simulation model of vertebrate population dynamics

that incorporates demographic, environmental and

genetic stochasticity (Salwasser pers. comm.) .l/

Such a modelling effort can be expected to make a

major contribution in wringing the most value from

the data at hand and helping to pinpoint the most

crucial data gaps. Expansion of this model from

a single isolated population format to a metapopulation configuration should provide a truly

useful tool, not only- for management but for

theoretical studies as well.

Short-Term Empirical Studies

For the northern spotted owl, short-term empirical

studies should focus on assessing reproductive

variability across a gradient of home-range sizes

by percent composition; some measure of the

genetic variability of the species; further work

to determine dispersal behavior and success; and

monitoring of suitable habitat, occupied and T+:

vacant, to assess the relative frequency of pair

extinction and the recolonization of patches.

Work on the latter item is underway (Carey 1985).

Efforts should also be made to determine why this .3

species prefers old growth. There is some

suggestion that prey availability may be the

greatest in old growth but that prey are abundant,

yet unavailable, in early successional stages

(Gutiérrez and others 1985). If this proves true,

silvicultural options may be available to enhance

the species' use of a wider variety of habitats.

Long-Term Monitoring of Management Actions and a

Research Program

To the extent that agencies must act now to

determine the species' habitat needs, the following

guidelines may serve as a reasonable approach

provided they are linked to the long-term monitoring

research program specified.

Patch Number. The goal of 500 breeding pairs

(Oregon Interagency Spotted Owl Management Plan),

in the absence of better guidance, should be

increased to 1,000 pairs for the subspecies. This

goal of 1,000 pairs would apply to Washington,

Oregon and northern California. While this number r

may seem large, it represents a 60 percent reduction from the most recant range-wide estimate

of the subspecies' abundance (U.S. Fish and Wildlife Service 1982). Moreover, given our current &

1

/ Hal Salwasser, National Wildlife Ecologist,

Washington Office, Wildlife and Fish Ecology,

3825 E. Mulberry Street, Ft. Collins, CO 80524.

96
understanding of the species genetic characteristics

(Barrowclough and Coats 1985) this increase

represents roughly a doubling of what would be

necessary to meet the admittedly rough minimal requirements for long-term adaptability (Franklin

1980) currently employed by the USDA Forest Service.

In addition, it should be noted that the emerging

SOMA patchwork will result in localized populations

of a size that will be extremely vulnerable to demographic stochasticity. Thus ei's can be expected

to be high. The low rates of survivorship and

pair establishment of juveniles during dispersal

(Allen and Brewer 1985, Gutiérrez and others 1985,

Wilson and Meslow 1985) indicate a low m value can

be anticipated. Recall that, for the species to

persist m must be greater than e. Adding SOMAs

should help assure this condition is met.

Further, if a management program is based on 1,000

pairs and no suitable unoccupied sites are reserved,

it is unlikely that 1,000 sites will always be

occupied (Salwasser and others in press). Thus

some effort should be made to determine the current

percentage of occupancy of suitable habitat and

then use this percentage to correct for the number

of patches necessary to actually maintain 1,000

pairs. All of these considerations point to a

need to increase the SOMA objective for the species,

at least until better information is available.

Patch size.--In the absence of better guidance,

SOMA size should be based on mean size and percent

composition of those areas sampled so far where the

subspecies has successfully bred. This could be

adjusted based on further sampling and the results

of the reproductive variability studies.

Distribution.--SOMAs should be located no more than

the median (Miller and Meslow 1985) distance of

documented successful dispersals. This is conservative but until more data are available it's

probably the prudent course to follow. Corridors

of mature or old-growth forest, particularly

riparian corridors, might aid inter-SOMA dispersal.

It is of concern that, to date, radiotelemetry

studies in Oregon and northern California have shown

very low survivorship rates for dispersing juveniles

(Allen and Brewer 1985, Gutiérrez and others 1985,

Miller and Meslow-1985). This inevitably raises

the question of whether habitat fragmentation has

already produced a metapopulation configuration

where m < e. These findings highlight the need for

more work on dispersal and adult survivorship, and

patch extinction and colonization rates.

A long-term monitoring research program should

focus on estimating adult survivorship; further

monitoring pair extinction and colonization rates;

and reproductive success across a gradient of SOMA

size/percent composition over time. Work should

also be instituted to determine what habitat manipulation techniques may be effective and feasible

to actively manage the species if it appears the

network of reserved areas is failing. It is

encouraging that the Pacific Southwest and Pacific

Northwest Regions of the USDA Forest Service are

actively pursuing the latter recommendation

(Salwasser, pers. comm. ) 2/

SUMMARY

The importance of island biogeographic theory to

conservation is the attention it has focused on

the importance of understanding localized extinctions and colonizations, and the factors affecting

these processes, as determinants of the distribution

and persistence of species. This focus has

triggered an increased appreciation of the role of

chance in determining the patterns manifest in

nature. The indications that such simple variables

as habitat size and isolation may play key roles

in determining population persistence in the face

of chance events is of crucial importance in an

increasingly fragmented world where the land-use

patterns imposed by man are often inimical to the

survival of certain species. Nowhere is this more

evident than in considering the fate of a species

whose patchwork of habitat is undergoing alteration.

If persistence hinges on the number, size, and

interrelationship of patches, at what point will

the fabric of habitat be stretched too thin and

the species lost? The northern spotted owl in the

Pacific Northwest is one current problem that fits

this scenario. A new paradigm, or perspective, on

population structure and dynamics is essential to

deal effectively with the conservation of such

species. The metapopulation concept seems an

appropriate frame of reference for this class-of

problem, yet ecological theory has yet to provide

a realistic model to assess even the qualitative

behavior of such a population configuration under

the influence of all the various types of stochastic

perturbations that are likely to affect populations.

Even without such models, common sense would indicate that a large number of large patches close

together should minimize the loss of species both

from particular patches and over all patches. Yet

further reasoning from common sense indicates that

there may be more subtle effects and these may

produce tradeoffs in habitat configurations which,

though spatially different, confer the same probability of persistence to the species in question.

Determining the existence and form of such tradeoffs is crucial to maximizing management alternatives to "fit nature in."

In the case of the northern spotted owl, valuable

data have been gathered but the effectiveness of

this information is constrained by the lack of

theoretical models to provide qualitative guidance

about which data are most important. The current

USDA Forest Service approach to the management of

this species (Salwasser and others, in press) is

encouraging but will benefit by expanding its

focus on genetic arguments to include the effects

of demographic and environmental effects. The

northern spotted owl highlights the whole issue of

land-use planning for the conservation of viable

populations. This issue is complicated by the

lack of a scientific consensus on standards for

what constitutes such a population and by the inescapable reality that we are being asked to project

2/ Hal Salwasser, National Wildlife Ecologist,

Washington Office, Wildlife and Fish Ecology,

3825 E. Mulberry Street, Ft. Collins, CO 80524..

97
the dynamics of a system without being given the

time to examine it empirically or experimentally.

I see no solution to this except that pointed out

by Salwasser and others (in press): to stimulate

theory to provide guidance and generate hypotheses

that may be tested in the context of the management

programs which will be implemented without complete

knowledge. I hope management will be allowed to

adapt in the future in the light of the experience

thus gained.

ACKNOWLEDGMENTS

I thank R. J. Gutiérrez, L. Ruggiero, H. Salwasser,

J. Nichols, M. Fuller, J. Ruos, E. C. Meslow, and

P. Opler for their helpful reviews of this manuscript. I would also like to thank P. Holt for

her tireless and proficient typing.

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648; 1976.

Simberloff, Daniel. Biogeography: the unification

and maturation of a science. In: Brush, Alan H.;

Clark, George A., Jr., eds. Perspectives in

ornithology. Cambridge, England: Cambridge

University Press; 1983:411-455.

Soulé, Michael E.; Wilcox, Bruce A., eds. Conservation biology: an ecological-evolutionary perspective. Sunderland, MA: Sinauer Associates;

1980. 395 p.

U.S. Fish and Wildlife Service. The northern

spotted owl. A status review. Portland, OR:

Endangered Species Program, U.S. Fish and Wildlife

Service; 1982. 29 p.

Vance, Richard R. The effect of dispersal on population stability in one-species, discrete-space

population growth models. American Naturalist.

123(2):230-254; 1984.

Wilson, Edward 0. Sociobiology: the new synthesis.

Cambridge, MA: Belknap Press; 1975. 697 p.

Wright, S. Joseph; Hubbell, Stephen P. Stochastic

extinction and reserve size: a focal species

approach. Oikos. 41:466-476; 1983.

99
A SUMMARY OF THE SCIENTIFIC BASIS FOR SPOTTED OWL MANAGEMENT

Andrew B. Carey

ABSTRACT: This paper is based on the presented papers and discussions at the

symposium "Ecology and Management of the Spotted Owl in the Pacific

Northwest: Conflicts and Opportunities" held in Arcata, California, in

1984. Additional information is drawn from published scientific reports and

unpublished administrative study reports. The information is synthesized

into a summary of the basis for managing spotted owls. Management for

spotted owls has generated controversy because of conflicts with timber

production and because there was little information on the ecology of the owl

prior to the 1970's. Substantial information on the spotted owl has now been

accumulated although much of this information has not been published. The

accumulated information shows that spotted owls need old-growth forest to

maintain healthy populations. Between 2,000 and 2,500 acres of old growth

are used, on the average, by a pair of spotted owls. Existing information

suggests that at least 1,000 pairs of northern spotted owls are necessary to

maintain a viable population. This will require maintaining more than 1,000

spotted owl management areas because not all SOKAs will be occupied.

Existing guidelines for distributing spotted owl management areas seem

adequate. Major informational needs include an inventory of old growth, an

assessment of how well present management is accomplishing goals for spotted

owls, quantitative data on spotted owl demography. and a greater

understanding of what constitutes a viable population. Monitoring the

results of spotted owl management will be essential to ensure that population

goals are met.

INTRODUCTION

A major problem for the resource management

agencies in the Pacific Northwest is ensuring

ANDREW B. CAREY is research coordinator,

Old-Growth Forest Wildlife Habitat Program,

Pacific Northwest Forest and Range Experiment

Station, Forestry Sciences Laboratory, 3625 -

936 Ave.. S.W., Olympia, Washington 98502.

that there is sufficient information for managers

about the spotted owl (strix occidentalis).

During the 1970's management for spotted owls

achieved regional prominence among wildlife

issues because of the owl's apparent dependence

on old-growth coniferous forests that also have

high value as timber. The spotted owl was v

described as declining in numbers because of

harvesting of timber and was accorded special

status by California, Oregon, and Washington

(Carleson and Haight 1985, Forsman and others

1982, Gould 1985, Heinrichs 1983, Juelson 1985). 3:

Because of its special status, its role as a

surrogate for other wildlife associated with old100
growth forests, and its prominence in the public

arena, the owl was designated a management

indicator species by the USDA Forest Service

(Carrier 1985, Lee 1985): During the 1980's the

d

spotted owl achieved national prominence because

of the conflict between harvesting timber and

ensuring that spotted owl populations remain

viable as required by the National Forest Management Act (Forsman and others 1982, Heinrichs 1983,

,-4 Meslow and others 1981). The controversy over the

spotted owl was exacerbated by the lack of information available in the 1970's on spotted owl

habitat requirements (Heinrichs 1983). Prior to

1977, the only published information was either

very general in nature or anecdotal and dealt with

individual observations of the bird and its

habitat, nests, and food habits. The first

quantitative study appeared in a scientific

journal in 1977 (Forsman and others 1977). The

results of many studies are still in unpublished

reports, manuscripts in preparation, or manuscripts in press (Campbell and others, in press).

Reviews of the owl's ecology that were used to

prepare management recommendations (for example,

Zarn 1974, Department of the Interior 1982) had

to be based on theses, anecdotes, unpublished

reports, and personal communications. Even now

there is only one major, published, scientific

treatment of the spotted owl in the Pacific

Northwest (Forsman and others 1984) and only a

few research reports in journals that require

rigorous technical review before publication

(Barrows 1981, Forsman and others 1977, Marshall

c

1942. for example). The symposium Ecologv and

Management of the Spotted Owl in the Pacific ---~

Northwest: Conflicts and Opportunities was

convened in 1984 (Gutiérrez and Carey 1985) to

bring together the rapidly accumulating informa-

‘i. tion on the spotted owl. This paper summarizes

the papers in that symposium and other published

and unpublished information to analyze the

sufficiency of information available to managers.

What Constitutes Sufficient Information?

To determine what constitutes sufficient

information for management purposes, six things

must be considered: (1) The objectives of the

managing agency. (2) The present management

situation and the options available to the agency.

(3) The accumulated information. (4) Forthcoming

information. (5) The state of wildlife science

in terms of the development of theory and reliable

predictive models. (6) Research needed and the

costs, difficulty, methods, and likelihood of

obtaining additional useful information in the

near future. Each of these is discussed. Much

of this analysis is directed towards the Pacific

Northwest Region of the USDA Forest Service

because it contains a majority of the remaining

?

habitat for northern spotted owl (S. o. caurina)

habitat. Habitat is also being managed by the

Pacific Southwest Region of the Forest Service,

and by the National Park Service, and Bureau of

Land Management in the U.S. Department of the

6 Interior.

OBJECTIVES OF THE MANAGING AGENCIES

Of all the laws relating to Forest Service

activities (U.S. Department of Agriculture 1983).

the National Forest Management Act of 1976

provides the clearest, most comprehensive

direction both for overall policy and objectives

and for managing forests for wildlife. The

regulations implementing the act (MacCleery 1982)

provide even more specific guidance: the dominant

principle of Forest Service planning and management is to "provide for multiple use and sustained

yield of goods and services from the National

Forest System in a way that maximizes long-term

net public benefits in an environmentally sound

manner." This balance between producing goods

and services and protecting the environment is

maintained throughout the act and the regulations

and is exemplified in specific, minimum requirements for management. These requirements include

maintaining the diversity of plant and animal

communities to meet multiple-use objectives and

providing habitat adequate to maintain viable

populations of existing native vertebrate species.

Both the Pacific Southwest Region and the Pacific

Northwest Region of the Forest Service recognize

that the spotted owl has special habitat needs

and that changes in its population may reflect

the effects of management activities. Both

regions have adopted plans to maintain viable

populations of spotted owls (Carrier 1985, Lee

1985). And both have recognized the value of oldgrowth coniferous forests as habitat for the

spotted owl and other wildlife and as an integral

component of natural diversity (Franklin and Spies

1984, Kerrick and others 1984, Salwasser 1984,

Sirmon 1984, Teeguarden 1984). Simply stated, the

Forest Service objective for spotted owls is to

provide an environment that will maintain viable

populations of spotted owls throughout their

existing range across the National Forests. But

the situation facing managers is not simple.

Because the spotted owl depends on mature and

old-growth forests, maintaining an environment

that is amenable to spotted owls will affect the

level of sustained yield of wood products. Viable

populations of spotted owls probably would be

maintained if mature and old-growth forests were

not harvested. But long-term net public benefits

might not be maximized. Although the National

Forest Management Act of 1976 emphasizes

production of goods and services, it also states

that multiple use is "not necessarily the

combination of uses that will give the greatest

dollar return or the greatest unit output."

Viable populations of spotted owls must be

maintained within a management arena that dictates

minimum impact on the harvest and production of

timber. Additional information on spotted owls

is required primarily because of the need to

balance spotted owl populations and wood products.

What kind of information do managers need to

achieve this balance? To a major extent, the need

for information is conditioned by the options that

are available. If, in the current management

situation, there is a great surplus of owls and

owl habitat, managers will have many choices. If

the spotted owls and their habitat are already

101
near minimum levels, few choices are left. If

suitable habitats can be created in a short time,

more options are available than if a long time is

required o- if habitat cannot be recreated.

If the management situation is favorable (many

options exist), then precise and accurate

descriptions of the requirements of spotted owls

could be used to select habitat management areas.

But if few options exist, then the information

that is more qualitative than quantitative would

be sufficient because few choices could be made.

The situation is complicated further by the lack

of a clear understanding of what constitutes a

viable population. Information on the spotted

owls must be placed in a theoretical framework

that defines "viable population." The theory is

relatively undeveloped as is the concept of

dependency of a species on particular types and

amounts of habitat (Barrowclough and Coats 1985;

Carey 1984; Shaffer 1981, 1985).

THE PRESENT MANAGEMENT SITUATION AND OPTIONS

AVAILABLE

Old Growth and Spotted Owls

Of the 15 million acres of old-growth (250-750

years old) forest (forests 250 to 750 years old)

present in the Pacific Northwest in the l800's,

about 5 million acres remain. About 1 million

acres are .reserved in national parks, wilderness

areas, and research natural areas in western

Washington and Oregon (Franklin and Spies 1984).

About 25 percent of the National Forests in the

Pacific Northwest west of the crest of the Cascade

Range consist of forests more than 250 years old

and amount to 2-l/2 million acres (Sirmon 1984).

Some of the old growth is subalpine forest not

suitable for spotted owls. The distribution of

old-growth (and mature) forest is not even. Old

growth is concentrated in the national parks and

in the National Forests along the west slope of

the Cascade Range. Old growth is not abundant in

the valleys and mountains west of the Cascade

Range except in parts of Olympic National Park.

The State of Washington, Department of Game, feels

that the remaining habitat on the Olympic

Peninsula is insufficient to support a viable

population of spotted owls (Juelson 1985).

Certainly the amount of old growth remaining in

the Olympic National Forest is insufficient

(Beckstead 1985). The State of Oregon, Department

of Fish and Wildlife, is concerned about the

population in the Oregon Coast Range because of

the relatively small amounts of old growth that

remain and because plans are to remove much of

the remaining old growth (Carleson and Haight

1985). The present populations of spotted owls

are about 1,200 pairs in Oregon (Carleson and

Haight 1985), 1,000 pairs in Washington (U. S.

Department of the Interior 1982), and 1,260 pairs

(of two subspecies) in California (Gould 1985).

These populations will probably decrease with

continued harvesting of mature and old-growth

timber (Forsman and others 1982).

The Spotted Owl Management Plan

Present management of spotted owls in National

Forests in Oregon and Washington is based on the

"Spotted Owl Management Plan" (unpublished) x

prepared by the Oregon-Washington Interagency

Wildlife Committee. The committee based its

recommendations on the preliminary results of

research conducted by Eric Forsman of Oregon

State University; the plan and the events relating b

to the formulation of the plan are summarized by

Forsman and others (1982). Forsman's research has

been published (Forsman and others 1984, Forsman

and Meslow 1985). The final recommendations of

the committee were adodpted by the Pacific Northwest Region (Lee 1985) and the Pacific Southwest

Region (Carrier 1985) of the Forest Service but

not by the Oregon State Office of the Bureau of

Land Management (Carleson and Haight 1985).

Initially both Federal and State agencies were

reluctant to adopt the committee's recommendations

because of the lack of information on spotted

owls. The state forestry agencies of California,

Oregon, and Washington still have not accepted the

recommendations. Even so, there is concern about

whether or not the Federal agencies are doing

enough (or conversely, doing too much at the

expense of other resources) for the spotted owl

(Carleson and Haight 1985, Gould 1985, Heinrichs

1983, Juelson 1985, La Follette 1979. Lee 1985).

Current management plans of Federal agencies

(Forest Service, National Park Service, and Bureau

of Land Management) would preserve the habitat of 9

800 to 1,000 pairs of northern spotted owls in the

Pacific Northwest. The Forest Service has set

goals of maintaining 530 pairs of spotted owls in

Washington and Oregon (Lee 1985) and 500 pairs (of

all subspecies) in California (Carrier 1985). Lv

Options

What options are there for managers? The Pacific

Northwest Region considered 533 pairs for its

minimum goal and 690 pairs as an alternative high

goal. Thus the managers in the Region had a fair

range of options available. But the Region is

reassessing the range of options, and the associated risks, through preparation of a supplemental environmental impact statement on the

regional guide for forest plans. Individual

National Forests in the Pacific Southwest Region

are also considering alternative goals. The

options available to the Bureau of Land Management

are not clear. The National Park Service is

charged with maintaining a natural environment, a

charge that is compatible with maintaining spotted

owl populations.

A full exploration of the options available to

the Federal management agencies has not been

possible because there is no inventory that

contains the locations, sizes, and characteristics of the mature and older stands not scheduled

for harvest. It is not possible without such an

inventory for researchers to determine the present 4

distribution of stands and the possible arrays

that could form alternative networks for maintaining spotted owls. It also is not possible to

select stands of specific structural characteris102
tics, sizes, and distributions to ensure that if a

minimum number of owls are maintained, they will

be maintained in the highest quality environment.

&a? THE ACCUMULATED INFORMATION

Spotted Owl Distribution

4 Bent (1938) reported that the spotted owl

inhabited a variety of forested environments in

western North America ranging from dense, coniferous forests in British Columbia to pine-oak woodlands in Mexico. However no sightings of spotted

owls have been reported in British Columbia in

recent years (Howie 1980). Until 1970, the

spotted owl was thought not to commonly occur in

the Pacific Northwest; only 24 sightings of

spotted owls in Oregon had been recorded (Forsman

and others 1982). Since 1972 numerous surveys for

spotted owls have been conducted by biologists

employed by Federal and State agencies, industry,

and private organizations. Some results have been

published (Erckman 1982; Forsman and others 1977,

1982, 1984; Garcia 1979; Gould 1977; Marcot and

Gardetto 1980; Postovit 1979); others have not

(many are listed by Campbell and others in press);

and some surveys are ongoing (for example, Allen

and Brewer 1985). Forsman and others (1982) tabulated many of the 1972-81 surveys: spotted owls

had been located at over 400 sites in California,

600 sites in Oregon, and 200 sites in Washington.

The population size for the northern spotted owl

(S.o. caurina, the subspecies in the Pacific d

Northwest) was estimated to be roughly 2,500

pairs (U. S. Department of the Interior 1982).

r” Spotted Owl Habitat

Survey results.--Although many of the sites surveyed by biologists have not been described using

standard, quantitative measures, the records show

the most spotted owls were found in late seral

forests; this substantiates the observations of

naturalists during the early 20th century that

the spotted owl was associated with old, virgin

forest.

Forsman and others (1984) describe 595 sites in

Oregon that were occupied by spotted owls, perhaps

50 percent of the occupied sites in Oregon. Most

(98 percent) of the sites were old-growth (more

than 200 years old) coniferous forests or virgin

forests that were mixtures of mature stands (100

to 200 years old) and old-growth stands. The

salient features of the occupied sites were: an

overstory composed of trees 230 to 600 years old;

an understory of trees 30 to 200 years old, canopy

closure averaging 65 to 80 percent as a result of

the uneven-aged, multilayered structure; and the

presence of broken tops, deformed limbs, and heart

? rot in large trees. Of 47 nests located. 90 percent were in the classic old growth just

described; the remainder were in younger forests

that contained scattered old-growth trees. Nest

:- trees averaged 49 inches in d.b.h. (diameter at

breast height) and none were less than 29 inches

in d.b.h. Nests were 39 to 180 feet above the __

ground averaging 75 feet in cavities or broken

tops of trees or on platforms of sticks and

debris on tree limbs.

Other, less extensive surveys gave the same

results as Forsman's. Cordano and Cordano,l/

surveyed dense stands of mature to old-growth

timber near streams in northern California. They

found owls in 80 percent of the stands. Marcot

and Gardetto (1980) surveyed a variety of stands

in northern California: 95 percent of the owls

they encountered were in mature or old-growth

stands, which occupied only one-third of the area

surveyed. Spotted owls were three times more

abundant in old-growth forests than in mature

forest. Gould (1977) describes 192 sites where

he found spotted owls in northern California. The

owls were found in dense, virgin, coniferous

forests between 98 feet and 7,500 feet elevation.

The sites contained mature forests with trees

greater than 33 inches d.b.h., a variety of tree

species, a multilayered canopy, canopy closure

greater than 40 percent, and a moderate degree of

decadence. In Oregon, Forsman and others (1977)

surveyed areas in the Cascade and Coast Ranges,

including extensive areas of second-growth forests

40-90 years old. Owls were 12 times more abundant

in old growth than in forests that were less than

80 years old. Postovit (1979) surveyed extensive

areas, including unbroken second growth, in the

Cascade Range and the Olympic Mountains of northwestern Washington. Spotted owls were five times

more abundant in old-growth forests than in

younger forests. Only one owl was found in

unbroken second growth. Abundance rapidly

declined with declining proportions of old growth.

Garcia (1979) surveyed stands of various ages in

the Gifford Pinchot National Forest in southwestern Washington. He found owls in stands

ranging in age from 60 to over 200 years old, but

his data were too few for comparing age classes.

Erckman (1982) found spotted owls to be widely

distributed in old-growth forests in the Mount

Baker-Snoqualmie National Forest in northwestern

Washington. He concluded that all old growth was

not of equal value to spotted owls. Areas below

3,200 feet in elevation and containing major creek

drainages had higher owl densities than higher,

drier sites. Forsman and others (1984) and Gould

(1977) also found altitudinal limits and commented

on the need for water.

Radio telemetry results.--Radio telemetry studies

of adult spotted owls in mosaics of old-growth,

mature, and young stands in western Oregon

(Forsman and others 1984) and northern California

(Gutiérrez and others 1984) confirmed the

association of spotted owls with mature and oldgrowth stands. Ongoing studies in Washington are

obtaining similar results (Allen and Brewer 1985).

In Oregon, home ranges of individual spotted owls

encompassed 1,356 to 8,349 acres, averaging 2,907

acres in the Cascades where 55 percent of the area

studied was in old growth and 4,725 acres in the

1/ Unpublished administrative study report,

1981, "A Preliminary Study of the Spotted Owl on

the Corning Ranger District," by Anette Cordano

and Marty Cordano, U. S. Department of

Agriculture, Forest Service, Mendocino National

Forest, 420 E. Laurel Street, Willows, CA 95988.

103
I

Coast Range where

was in old growth

20 percent of the area studied

The amount of old growth

encompassed in the home ranges was 741 to 2,878

acres, averaging 1,988 acres in the Cascades and

1,245 acres in the Coast Range. None of the six

pairs of spotted owls studied had less than 1,008

acres of old growth in its range (Forsman and

others 1984, Forsman and Meslow 1985). The

average amount of old growth in a pair's range

was 2,264 acres (Forsman and Meslow 1985). These

figures and all the figures for owls in the Coast

Range are based on only 4 months of study during

summer. In the Cascade Range, owls were studied

from 9 to 13 months; the data indicated that 4

months of study are insufficient to adequately

determine total home range use. The owls used old

growth for foraging 64 to 99 percent of the time

despite the low proportions of their ranges in

old growth (20 to 66 percent). Owls spent 0 to

16 percent of their time foraging in mature stands

and 0 to 36 percent in young (61 to 80 year old)

stands. The owls also foraged in 25- to 35-yearold forests in the Coast Range (0 to 31 percent

of the time) but not preferentially (up to 47

percent of the home ranges were 25- to 35-year-old

forests). The only preference (use out of proportion to occurrence) demonstrated was for old

growth. More than 1,600 roosts were located; 91-

98 percent were in old-growth forest; 90 percent

of the nests located were in old-growth forest.

Preliminary results of two northern California

studies were reported by Gutiérrez and others

(1984). Home range sizes for six owls were 741

to 3,705 acres or an average 2,245 acres. Home

ranges of adult pairs exceeded 3.000 acres and

contained more than 2,000 acres of mature and

old-growth forests. Mature and old-growth forests

comprised 22 to 52 percent of summer home ranges

and 11 to 66 percent of winter home ranges.

Mature forests in the California study area were

more than 150 years old and had multilayered

canopies; dominant trees were larger than 39

inches d.b.h. 2/

3/ Late seral stage forests

were used out of proportion to their occurrence.

Data analysis is incomplete, but results to date

agree with the results reported by Forsman and

others (1984) (Gutiérrez and others 1984). In

both studies home range size increased as the

proportion of old growth decreased, further

substantiating the need for some minimum area of

mature and old-growth forest.

A correlation was also found in radio telemetry

studies in Washington between home range size and

the amount of old growth contained in the home

range. Three adult pairs had an average of 1,850

acres of old growth in their home ranges (Allen

and Brewer 1985).

Summary of spotted owl habitat.--Spotted owls in

the Pacific Northwest use all the major coniferous

forest associations except subalpine forests and

forests of ponderosa pine (Pinus ponderosa Dougl.

ex Laws), lodgepole pine (p. contorta Dougl. ex

Loud.), or sitka spruce (Picea sitchensis (Bong.)

Carr.). Some hardwood stands are used. Spotted

owls are most abundant in old-growth forests

characterized by an uneven-aged, multilayered

canopy with a high composite canopy closure.

Dominant trees are large (39 inches d.b.h. or

larger) and old (over 230 years) and many have

broken tops. cavities, or deformed, platform- e

2/Personal communication, R. J. Gutiérrez.

Humboldt State University, Arcata, CA 95521.

3/ Unpublished administrative study report, b/Unpublished Administrative Study Report, "A d

"Winter Ecology of Radio-Tagged Owls on Six Rivers test of a spotted owl habitat suitability model,"

National Forest, Humboldt County, CA," by Chuck by Stephen A. Laymon, University of California,

Sisco. Humboldt State University, Arcata, CA Berkeley, College of Natural Resources, Berkeley,

95521. CA 94721.

Laymon (1985) is conducting radiotelemetry

studies on California spotted owls (S. o.

occidentalis) in the Sierra Nevadas. He has

observed a marked altitudinal shift in home range

from summer to winter. The four owls he monitored

moved 12 to 20 miles to areas that were an average

t

of 2,296 feet lower in elevation than were the

summer home ranges. These owls returned to their

summer home ranges in the spring. Seasonal

adjustments in home range have been noted by all ‘5

the biologists studying the northern spotted OWl,

but none of these adjustments approached the

migratory nature of the California spotted owl

observed by Laymon. Laymon's research underscores

the importance of studying a species throughout

its range.

Radio telemetry studies have shown that .

dispersing juvenile spotted owls will frequent

young forests and even clearcuttings. But

mortality rates of juveniles are very high.

Juveniles have the capability to disperse long

distances before dying (up to 61 miles, but

averaging 15 to 28 miles, depending on the

area). There is no such information on

successful dispersers (owls that disperse,

establish a territory, mate, and produce

offspring). The juveniles do not cross large

bodies of water (for example, reservoirs or Hood

Canal). They will cross rivers 246 to 328 feet

wide. They often disperse along forested

corridors, such as riparian areas, and they will

cross ridges. Studies of dispersing juveniles

are being conducted in California, Oregon, and

Washington (Allen and Brewer 1985, Gutiérrez and

T

others 1985, Laymon 1985, Miller and Meslow 1985).

A test of a habitat model.--Laymon 4/ developed

a Habitat Suitability Index model for spotted

owls based on Forsman's research with some

consideration of other studies. The model

includes tree size, canopy closure, vertical

layers of vegetation, and area. The model was

tested on the Eldorado National Forest in

California. The test confirmed the association

of spotted owls with large trees (greater than 36

inches d.b.h.), high canopy closure (70 to 100

percent), and multilayered understory.

'6"

104
forming branches. Understory trees are 30 to 200

years old. Some of the understory trees are

small, often are deciduous (such as vine maple,

Acer circinatum Pursh.) and provide perches-almost

4 to the forest floor. Abundance of spotted owls

varies with the proportion of old growth in the

forested landscape. But the owls can do well in

mosaics of old-growth, mature, and young stands.

li. In extensively harvested forests, spotted owls

expand their home ranges as fragmentation

increases, presumably to maintain some minimum

amount of old growth within their ranges.

Averages (depending on area) are 1,850 to 2,265

acres of old growth per pair. Obviously, the

owls cannot expand their range indefinitely

(observed ranges are 1,356 to 8,349 acres); as

they reach the higher limits their ability to

survive and reproduce must be diminished. The

average home range size in highly fragmented

forests is around 4,693 acres and can be used as

a basis for management. An area of 4,849 acres

is encompassed by a circle with a radius of 1.5

miles. Forsman and others (1984:57) felt that

988 acres of old growth within 1.5 miles of a

nest tree would be adequate habitat for a pair of

spotted owls, even when the remaining acreage was

covered by stands less than 80 years old. The

988-acre recommendation was based on the least

amount of old growth in the home ranges of the

pairs of owls Forsman studied. One pair, studied

for 4 months, had 1,008 acres of old growth in

its home range. No other pair had less than

2,092 acres of old growth in its home range

s (Forsman and Meslow 1985). Habitat management

for spotted owls could be based on the average

amount of old growth used by pairs in the Pacific

Northwest (1,850 to 2,265 acres). For example,

i

if 2,470 acres of old growth were maintained along

with stands of a variety of other ages (including

80- to 200-year-old trees) within a 1.5 mileradius-SOMU (spotted owl management unit-habitat

for one pair), the chance of maintaining a pair

of spotted owls in a SOMU would be substantially

improved. If use of the SOMU by a pair of owls

were documented, the manager could then be

reasonably confident that the SOW was

contributing to maintaining a viable population

of spotted owls.

How reliable is the above information? Forsman's

studies (Forsman and others 1977, 1984) and

Gould's studies (1977, 1985) were based on

unusually large sample sizes compared to other

studies of raptors. The results of these studies

were confirmed by smaller studies and by the

preliminary results of two recent studies in

California (Gutiérrez and others 1984, Gutiérrez

1985) and ongoing studies in Washington (Allen

and Brewer 1985). But only a dozen pairs of

adult owls have been studied with telemetry.

Additional quantitative data will be forthcoming

* (Carey and Ruggiero 1985). It is unlikely that

the description of suitable environments and the

minimum recommendations will be lowered by forthcoming data, but data specific to a state or

L

region are being gathered. Some tailoring of

habitat management to local conditions may be

possible.

Determinants of Habitat

Why are spotted owls associated with old-growth

forests in the Pacific Northwest? A number of

reasons have been proposed; they can be grouped

into six loosely-formulated hypotheses that are

not mutually exclusive: nesting hypothesis,

heat-stress hypothesis, prey-abundance

hypothesis, prey-availability hypothesis,

predation hypothesis, and adaptation hypothesis.

Nesting hypothesis.--Old-growth forests are more

likely to contain trees that are structurally

suited for nests than are young forests. The

spotted owl does not construct a nest. It must

therefore find natural platforms that are suited

for holding the female, eggs, and young birds.

Because the spotted owl is a large bird, the

platform must be large. To safeguard the eggs

and young from terrestrial and semiarboreal

predators the nest must be high above ground.

Thus the platform must be part of a large tree.

Suitable platforms include large cavities in

trees, depressions in the broken tops of trees,

and platforms resulting from the accumulation of

organic material on the fan-shaped branches of

old-growth trees. This hypothesis is supported

by the descriptions of the nests of spotted owls

that have been found in Pacific Northwest forests

(Forsman and others 1984).

Heat-stress hypothesis.--Spotted owls are

intolerant (compared to many other owls) of high

temperatures and are stressed at temperature above

27 to 31°C (depending on wind speed). This

temperature intolerance is a function of the owl's

plumage which is adapted for withstanding the

stress of cold winter temperatures (Barrows 1981,

Barrows and Barrows 1978). The tall, multilayered

canopy of old-growth forests results in a larger

gradient in temperature (and amount of direct

solar radiation) than exists in forests with

shorter, simple, canopy structure. The multilayered canopy provides roost perches that range

from high in the canopy down to ground level. In

particular, hardwoods in the understory (such as

vine maple) allow roosting close to the ground.

Field studies of roosting behavior and heat stress

have employed meterological equipment, radio

telemetry, direct observation, and characterization of roosts and roost-stands. Owls change

roosts (especially height) and body posture to

avoid direct sunlight in the summer and to find

ambient temperatures lower than 27 to 31°C.

Stands in California used for roosting were often

on north-facing slopes and in canyons. Owls in

California have also been observed to change

roosting locations to be near water and, when

heat stress still resulted in physiological

reactions (gular flutter), to bathe (Barrows

1981, Barrows and Barrows 1978). Owls in Oregon

exhibit similar behavior, but unexpectedly most

owls in the Coast Range roosted in stands on

south-facing slopes (Forsman and others 1984).

The putative association of spotted owls with

old-growth stands that contain streams or seeps

lends further support to the heat-stress

hypothesis, as does the association of spotted

owls with caves and canyons in the Southwest.

Laymon (1985) observed altitudinal shifts in home

range in the Sierra Nevada with the owls using

105
higher elevations in the summer than in the

winter; the reasons for these shifts are net

known at this time but the phenomenon does fit

this hypothesis. The hypothesis does not explain

why spotted owls are not known to occur at high

elevations in Oregon and Washington.

Prey-abundance hypothesis.--Spotted owls prey on

a wide variety of animals. They specialize in

small mammals such as red tree voles (Arborimus

longicaudus), deer mice (Peromyscus maniculatus),

dusky-footed woodrats (Neotoma fuscipes), and

northern flying squirrels (Glaucomys sabrinus);

the latter two species are preferred--the woodrat

in mixed conifer forests in California and Oregon

and the flying squirrel in Washington and most of

Oregon (Barrows 1985, Forsman and others 1984).

A greater diversity of prey is eaten by spotted

owls in the Sierra Nevada, with gray squirrels

(Sciurus griseus) and birds assuming importance

(Layman 1985). Barrows (1985) has noted that

owls that eat a high proportion of large prey

(flying squirrels and woodrats) have greater

success in breeding than do owls that eat small

prey. Owls expend less energy per unit of food

in capturing the large prey, thus presumably more

energy is available for reproduction than when

the majority of the prey is small animals. A

hypothesis has been advanced that the preferred

prey is more abundant in old-growth forests than

in younger forests. Raphael and Barrett (1984)

found small mammals, as a group, more abundant in

"large timber" than in "medium timber" or "small

timber." Dusky-footed woodrats and deer mice were

more abundant in forests older than 250 years than

in forests 150-250 years old or younger than 150

years. Both species were also abundant in shrubsapling stages. Raphael and Barrett did not,

however, adequately sample northern flying

squirrels. Thus there are few data to support

the hypothesis. Ongoing studies by the Forest

Service (Ruggiero and Carey 1984) will answer the

questions about prey abundance across the sere of

forest development.

Prey-availability hypothesis.--The preyavailability hypothesis differs from the

prey-abundance hypothesis by stating that the

prey of the spotted owl is abundant in old growth,

but not necessarily more abundant there than

elsewhere. The key feature is that the structure

of old-growth forest is better matched to the

spotted owl's size and method of foraging than

the structure of younger forests and that this

structure results in a greater availability of

prey (more of what is there can be caught) than

other environmental structures. Gutiérrez and

others (1984) mention this hypothesis. Foraging

perches are more available in old growth, and

patchiness in the understory and gaps in the

canopy may provide a better environment for

foraging than do young forests. Testing this

hypothesis in field studies would be difficult,

but Forsman and others (1984) observed foraging

behavior and documented that spotted owls select

old growth for foraging. Their study lends

support to the hypothesis. Gutiérrez and others

(1984) reported that they had unpublished data to

support the hypothesis also. Some of these data

include observations of spotted owls using perches

in riparian corridors and in the edges of oldgrowth and mature forest to search for prey in

clearcuttings and brushfields.5/

Predation hypothesis.--Great horned owls (Bubo

virpinanus) will prey upon juvenile spotted owls

(Forsman and others 1984, Gutiérrez and others

1985, Miller and Meslow 1985); thus it is

hypothesized that spotted owls use old growth or

avoid open areas) to avoid predation by great

horned owls. The evidence for this hypothesis is

anecdotal as there is no evidence of intensive

predation on adult spotted owls or that predation

on juveniles is anything but opportunistic. It is

generally accepted however, that dispersing

juveniles of most species are especially vulnerable

to predation. The apparent reluctance of both

juveniles and adults to cross large open spaces

like large bodies of water may reflect this

vulnerability. Extensive forest fragmentation

could affect the ability of juveniles to disperse

successfully. I

Another interspecific interaction may become

important. Barred owls (Strix varia) are extending

their range and are now found in western Washington, Oregon, and California. The barred owl is

very much like the spotted owl, except it seems to

be more versatile. The barred owl may become a

serious competitor of the spotted owl Gutiérrez

and others 1984, Taylor and Forsman 1976). Harriet

Allen6/ has been recording sightings of barred

owls and monitoring adjacent pairs of barred owls

and spotted owls to determine how they interact.

Adaptation hypothesis .--The adaptation hypothesis

states that spotted owls are behaviorally and

physiologically adapted to old-growth forests

simply because old growth has been the dominant,

stable feature of the landscape for many

generations of spotted owls. This hypothesis

would be impossible to test. There is some

evidence that spotted owls do exhibit behaviors

such as site tenacity (Forsman and others 1984).

Old growth may be a "niche gestalt" (James 1971)

for dispersing juvenile--in other words,

dispersing juveniles seek areas of a certain

structure that are not occupied by adult owls and

settle in such areas as a response to the

structure. This response could be innate or it

could reflect the owl's fledging environment.

Summary of determinants of habitat.--The various

hypotheses and the supporting evidence provide a

description of spotted owl life requirements that

eliminate the need for terms like old-growth,

mature, and young forests. It is clear that

spotted owls need stands: (1) that are multilayered with an understory (often containing

b

Q

5/ Unpublished adminstrative study report,

"Winter Ecology of Radio-Tagged Spotted Owls on

Six Rivers National Forest, HUM ldt Co., CA,” by

Chuck Sisco, Humboldt State University, Arcata. CL

95521.

6/Personal communication, Harriet Allen.

Washington Department of Game, 6OC North Capitol

Way, Olympia, WA 98504.

%

106
hardwoods), a midstory, and an overstory; (2)

that contain large (39 to 67 inches in d.b.h.)

trees that contain cavities, depressions in '

broken tops, or platforms of large branches and

organic debris at least 33 feet above the ground;

4 and (3) that concomitantly support abundant

populations of small mammals, particularly flying

squirrels or woodrats. Large, fallen, decayed

trees contribute to the abundance of small mammals

4, (Maser and Trappe 1984) and streams and seeps

would further raise the quality of the stand for

spotted owls. Many will equate such stands with

old growth as described by Franklin and others

(1981) and Franklin and Spies (1984). Franklin

and others (1981) suggested that old-growth stands

should be maintained in blocks of 296 to 494 acres

to maintain their ecological characteristics. And

that 494 to 988 acres of old growth are needed to

influence the character of a third-order stream

drainage. Empirical data (Forsman and others

1984, Gutiérrez and others 1984) indicate that

2,470 acres will make 7.7 square miles suitable

for one pair of spotted owls. The greater the

proportion of the landscape in multilayered and

closed-canopy stands, the greater the number of

pairs of spotted owls that can be maintained.

Managing for Viable Populations

Federal regulations direct the Forest Service to

maintain viable populations of indigenous

wildlife. The regulations state that a viable

"one which has the estimated numbers

.g

population is

and distribution of reproductive individuals to

insure its continued existence is well distributed

in the planning area" (MacCleery 1982). Habitat

must be managed not only to maintain this minimum

4 number but also to ensure interaction among the

individuals. The key phrases in the regulations

are "continued existence," "well distributed,"

"interact with others," and "habitat must be

provided."

Continued existence of spotted owls.--Federal and

State agencies plan to maintain 800-1,000 units

of habitat suitable for pairs of spotted owls in

northern California, Oregon, and Washington to

ensure the continued existence of spotted owls.

The Pacific Northwest Region of the Forest

Service plans to maintain 530 of these SOMUs (Lee

1985). The adaptive management approach to

managing for viable populations that is used by

the Pacific Northwest Region is summarized by

Salwasser and others (1984).

Two classes of factors work against the continued

existence of wild populations: systematic factors

are continuing or recurring events; stochastic

factors are unpredictable or random changes in a

species' demography, environment, or genetics and

natural catastrophes (Shaffer 1981, 1985).

3

Systematic factors include expanding human

populations, land use changes, and timber

harvests. The migration of spotted owls between

i midelevation federal lands and low-elevation

private lands in the Sierra Nevada subjects the

owls to land use changes brought about by

expanding human populations. Although the

development is on private land, owl populations

on federal lands are affected (Laymon 1985).

Systematic harvests of timber have reduced the

amount of spotted owl habitat; continuing harvests

in the Coast Range are jeopardizing the continued

existence of spotted owls there (Carleson and

Haight 1985). Land exchanges among Federal

agencies and private landowners and timber harvest

on private land affect spotted owls and management

of spotted owl habitat on federal lands in Oregon

and Washington (Ruediger 1985). Past systematic

timber harvest, including timber harvests on

Federal land, has jeopardized the spotted owl

population of the Olympic Peninsula (Beckstead

1985, Juelson 1985). Forsman and others (1982)

conclude that if the trends in timber harvest

continue, spotted owls will become rare in the

Pacific Northwest.

Demographic stochasticity refers to chance events

in survival and reproductive success. Spotted

owlssuffer accidents, are preyed on occasionally,

and are variable in producing young from year to

year (Barrows 1985, Forsman and others 1984;

Gutiérrez 1985; Gutiérrez and others 1984, 1985;

Miller and Meslow 1985). The survival of

juveniles from hatching, through fledging and

dispersal, to establishing a territory and

acquiring a mate is subject to so many chance

events that it is rare (Allen and Brewer 1985,

Gutiérrez and others 1985, Miller and Meslow

1985). The structure of a population (sex ratio,

age structure, proportion of adults that breed)

may reflect many random events.

Environmental stochasticity includes temporal

variation in weather, in the owls' habitat, and

in the species populations the owls interact

with--prey, competitors, and parasites. Ongoing

studies by the Old-Growth Forest Wildlife Habitat

Program (Forest Service) are documenting marked

annual variation in the population sizes and

reproduction of the small mammals that serve as

prey for spotted ow1s. 7/ Juvenile spotted owls

are sometimes killed by great horned owls or

other raptors (Forsman and others 1984, Gutiérrez

and others 1985, Miller and Meslow 1985). The

probability of an owl being preyed on is partially

a function of the pattern of abundance of its

potential predators, which in turn is a function

of systematic and stochastic factors that affect

the predators' populations and is due partially

to chance. A potential competitor of the spotted

owl, the barred owl, is expanding its population

in the Pacific Northwest and may usurp some of

the habitat maintained for spotted owls (Taylor

and Forsman 1976, also see footnote 6). Present

interactions between the two species are rare and

by chance; in the future, barred owls could bring

systematic pressure to bear on spotted owls.

Juvenile owls leave the nest before they can fly

probably because of increasing numbers of

parasites in the nest (Forsman and others 1984).

Leaving the nest at an early age increases the

susceptibility of young owls to accidents and

7/Unpublished data on file. Forestry Sciences

Laboratory, 3625 - 93d Avenue SW, Olympia, WA

98502.

107
predation. Ruediger (1985) documents how

unpredictable changes in habitat, such as

destruction by high winds or by small wild fires,

have affected the carrying capacity of the Gifford

Pinchot National Forest for spotted owls.

There are no data on the genetics of spotted owls,

but Barrowclough and Coats (1985) discuss spotted

owl demography in the light of current genetics

theory. They illustrate how chance genetic events

can be of great importance when populations are

small. They also point out the differences

between effective population size and total

population size. Effective populations (from a

demographic-genetic standpoint) are much smaller

than total populations.

Natural catastrophes play an important role in

forest ecosystems in the Pacific Northwest. The

nature and distribution of old-growth forests are

results of catastrophic fires that occurred 200-

1,200 years ago (Franklin and Dyrness 1973).

Large areas of spotted owl habitat in the Cascade

Range of southern Washington were destroyed in

the early 1980's by the volcanic eruption of Mount

St. Helens (Ruediger 1985). There is an interplay

between systematic and stochastic factors.

Systematic factors may depress population levels.

At low population sizes, stochastic factors are

of great importance. In at least two areas (the

Coast Range in Oregon and the Olympic Peninsula

in Washington) systematic factors have reduced

spotted owl populations to the level where

stochastic events may determine whether or not

the populations persist. Indeed spotted owls

have already been essentially eliminated from the

Coast Range in northern Oregon and southern

Washington. In other areas (northern California

and the Cascade Range in Oregon and Washington)

systematic factors continue to deplete spotted

owl habitat and are probably a greater influence

on spotted owl populations than are stochastic

events. Barrowclough and Coats (1985) suggest

that the 800-1,000 SOMUs (habitat for one pair)

planned for the Pacific Northwest will be adequate

to minimize stochastic demographic and genetic

effects in a "best case,, implementation

scenario. Shaffer (1985) concludes that more

than 1,000 SOMUS must be provided to maintain the

1,000 pairs of adult owls that he feels are

necessary to minimize stochastic environmental

effects. Ensuring 1,000 pairs requires more than

1,000 SOMUs because not all SOMUs will be occupied

by pairs all the time.

Distribution.--Forest Service guidelines for

spotted owl management incorporate requirements

for distribution and interaction. 8/ Spotted

owl management areas (SOMAs) are to provide

habitat for three or more pairs of spotted owls

and are to be 12 miles or less apart. Single-pair

SOMAs (equivalent to a SOMU) are to be established

8/Unpublished administrative document, 1983.

"Regional Guidelines for Incorporating Minimum

Management Requirements in Forest Planning,, Jeff

M. Sirmon. Pacific Northwest Region, USDA Forest

Service, 319 S.W. Pine Street, Portland, OR 97208.

\

108

only to improve the distribution of SOMUs and must

be 6 miles or less from other SOMUs. Implementation of the guidelines for distribution and interaction has required more SOMAs than were thought

necessary for continued existence from the standpoint of population size (Beckstead 1985, Carrier x

1985, Lee 1985. Ruediger 1985). These guidelines

still seem reasonable in the light of additional

information on spotted owl dispersal Gutiérrez

and others 1985, Miller and Meslow 1985). It is i.-

difficult however, to meet the guidelines in the

Coast Range (Carleson and Haight 1985) and on the

Olympic Peninsula (Beckstead 1985). The guidelines do not (and cannot) ensure interaction

among all spotted owl populations. The population

on the Olympic Peninsula seems to be isolated from

all others by Puget Sound, extensive human

development in the Puget Trough, and large areas

of unsuitable habitat in the Chehalis Valley and

southward. The populations in the Cascade Range

in Washington may be isolated from those in the

Cascade Range in Oregon by the Columbia River.

Similarly, the Willamette Valley may separate

Coast Range populations from Cascade Range

populations in Oregon. And the guidelines do not

account for stochastic environmental events,

catastrophes, or chance demographic events that

result in unoccupied SOMAs. The guidelines

assume that SOMAs will persist indefinitely and

will be occupied routinely.

Habitat.--Simply defined, habitat is the area

occupied by one or more individuals of a species.

The Pacific Northwest Region management guidelines

(see footnote 8) define the requirements of a

T

reproducing pair of spotted owls as 300 acres of

old growth in a core area around a nest and an

additional 700 acres of old growth in patches

larger than 30 acres within 1.5 miles of the nest. 5-

If there is not 1,000 acres of old growth within

1.5 miles of the nest, then the oldest stands

available may be substituted for the lacking old

growth.

It has not been possible to locate SOMUs on the

basis of actual nesting sites and home ranges;

SOMUs and SOMAs have been established using crude

surveys for spotted owls and old growth and to

minimize land-use conflicts (Beckstead 1985,

Ruediger 1985). To be effective, SOMAs must

contain pairs of adult owls that fledge young

from time to time. It is not safe to assume that

all l,OOO-acre areas of old growth (or a mixture

of old-growth and mature forest) will contain a

reproductively active pair of spotted owls. In

general, old growth is habitat for spotted owls.

But in specific instances, to be habitat the

forest must contain nesting, roosting, and

foraging-sites, a sufficient abundance of prey, a

suitable microclimate, and spotted owls to be

habitat. The l,OOO-acre guideline is based on

the smallest area of old growth known to support

a pair of spotted owls in a heavily fragmented \F

forest for a 4-month period; the average acreage

of old growth per pair in that forest during the

4 months was over 2,000 acres (Forsman and Meslow

1985). Thus one would expect, and experience has &

shown, that many apparently suitable areas (as

defined by the guidelines) do not contain spotted

owls (Beckstead 1985, Ruediger 1985). Therefore

the size and character of SOMAs must be ultimately
determined by verification procedures and

monitoring (see Carey and Ruggiero 1985). One

approach would be to designate more than 1,000

acres of old growth per pair until occupancy of

A

the SOMAs has been verified and monitoring has

shown that pairs are reproducing and that most

spotted owl pairs can exist and fledge young with

1,000 acres of old growth.

4 Summary of managing for viable populations.--The

accumulated information relevant to ensuring

viable populations of spotted owls in the Pacific

Northwest includes the following findings and

conclusions:

1. The existing guidelines for the network

distribution of SOMA's still seem reasonable in

view of recent research on dispersing owls.

2. Original studies showed that the average

amount of old growth in the ranges of owl pairs

is around 2,200 acres. Subsequent studies

corroborated that work.

3. Distributional guidelines require a network

of 800-1,000 spotted owl management units. A

demographic analysis concentrating on genetics

concludes that 1,000 pairs of owls would be

adequate for ensuring continued existence

throughout the existing range only in a "best

case,, scenario. And a viable population analysis

considering systematic and stochastic factors

conclude that more than 1,000 management units

'W would be necessary to maintain 1,000 pairs of

owls. The viable population analysis is

corroborated by case histories of implementation

of spotted owl management plans and the

preliminary results of a monitoring program for

5 spotted owls.

4. Monitoring can be used to determine occupancy

rates and rates of loss of habitat. The results

of monitoring could be used to determine how many

management areas would have to be set aside to

ensure that a minimum of 1,000 pairs of spotted

owls would be maintained and what margin of

safety (additional management units) would be

necessary to offset loss of management units to

unforeseen events.

5. Management for viable populations of spotted

owls will be effective only if there is close

collaboration among land management agencies to

implement a common management scheme. That

situation does not exist today. State and Federal

agencies have not adopted the same guidelines.

The Forest Service, which manages the majority of

the remaining suitable habitat, is carrying the

primary burden of owl management. Also, the

National Park Service, because of its mission to

maintain natural environments, is protecting the

spotted owl habitat on its lands.

FORTHCOMING INFORMATION

‘, A review of ongoing research and monitoring

Gutiérrez and Carey 1985) reveals that a

significant amount of new information is being

gathered on spotted owls. Research on the

seasonal movements of spotted owls in the Sierra

Nevada is continuing. State wildlife agencies

are compiling inventories of actively used spotted

owl territories in California and Oregon and

estimates of the statewide population in Washington. Habitat use by adult owls is being described

in California and Washington. Breeding, reproductive attainment, and dispersal of juvenile owls is

being studied in California, Oregon, and Washington. Information on the food habits of spotted

owls is being accumulated throughout the Pacific

Northwest. SOMA occupancy rates and spotted owl

home ranges are being determined in Washington.

The Bureau of Land Management is planning a

monitoring study in Oregon that also will

determine occupancy rates and reproductive

attainment.9/ In California, the Bureau of

Land Management is determining the effect of

timber harvesting on nearby spotted owls.10/

THE STATE OF WILDLIFE SCIENCE

Wildlife managers and researchers are addressing

the problem of ensuring the continued existence

of regional populations of species that are

jeopardized by the accumulating impacts of human

activities (see Lehmkuhl 1984 and Shaffer 1981).

But theory and management concepts are still

poorly developed. And case histories and

empirical data are lacking. Theoretical

constructs for defining dependencies of species

on particular types of environments or elements

of the landscape are not yet supported by

successful application to real situations (Carey

1981, 1984; Crowley 1978; Van Home 1983).

Theories for determining the patterns of

abundance (numbers, sizes, spatial distributions)

of suitable environments that will maintain

sufficient numbers of individuals for the species

to persist despite systematic pressures and

stochastic demographic, genetic, and environmental events are just being developed. Concepts

for determining minimum viable populations have

been proposed (Lehmkuhl 1984, Salwasser and

others in press, Shaffer 1981) but not tested.

Many authors have addressed the general aspects

of population genetics as related to conservation

(see Schonewald-Cox and others 1983 and Soulé and

Wilcox 1980 for examples), but very little is

known about the role genetic events play in wild

populations. For this paper, I applied concepts

of dependency to the problem of ensuring the

continued existence of spotted owls in the

Pacific Northwest. Shaffer (1985) applies the

concept of minimum viable populations to spotted

owl management. Barrowclough and Coats (1985)

9/Unpublished draft plan, 1984, "Northern

Spotted Owl Management Plan,, by the U. S.

Department of the Interior, Bureau of Land

Management, Oregon State Office, 825 NE Multnomah

Street, Portland, OR 97232.

10/Personal communication, C. J. Ralph, Redwood

Sciences Laboratory, 1700 Bayview Drive, Arcata,

CA 95521.

109
examine spotted owl management from a population

genetics standpoint. It is evident from these

three papers that long-term, empirical,

demographic studies will be necessary if there

are to be definitive answers to questions about

the viability of spotted owl populations. But

the need for further development of theory and

concepts is also evident.

INFORMATION NEEDS

Three types of studies are needed to refine

spotted owl management: monitoring studies,

demographic studies, and region-specific studies.

Monitoring Studies

The most immediate need for information is to

determine how well the present management is

working. Are owls using spotted owl management

areas? Are the owls in SOMAs routinely producing

young? What happens when the old growth in a

SOMA is gradually reduced to the l,OOO-acreper-pair standard? How long does it take a

vacated SOMU to be recolonized? A monitoring

program to answer some of these and related

questions for the SOMAs in Washington is

described by Carey and Ruggiero (1985).

Demographic Studies

A major gap in the knowledge of spotted owl

biology is spotted owl demography. What are the

life expectancies of owls? At what age do owls

first mate to produce young? What are the age

structures of various populations? What are

common rates of reproductive attainment? What

are the rates of recolonization of vacated

territories? What are common effective

population sizes? What is the genetic diversity

of the various populations in the Pacific

Northwest? Is there regular exchange of genetic

material among the various populations in the

Pacific Northwest? How are demographic

parameters affected by forest fragmentation and

increased isolation of breeding pairs?

Estimates of demographic parameters can only be

gained through long-term (10 years or more)

studies of large numbers of owl territories (say

45-100) in each of the six major geographic areas

of the Pacific Northwest. To be effective, both

adult and juvenile owls would have to be banded

in the study areas. During capture of the owls

blood samples could be taken for genetic studies.

Genetics could, thus, be a part of the study of

demography. Because of the large-scale nature of

the studies, they would have to be cooperative in

nature. Demographic studies could capitalize on

monitoring studies but it is unlikely that

monitoring studies would be conducted for long

enough periods to substitute for demographic

studies. Demographic studies are expensive and

would not provide managers with definitive

information in just a few years. The information

from the demographic studies would be most

appropriate for building population models and

for contributing to theories about minimum viable

populations. The empirical data, models, and

theories could then be related to management.

Region-Specific Studies

Most work on northern spotted owls has been

conducted in Oregon and northern California.

Information on habitat use that is specific to

the Olympic Peninsula and Cascade Range in A

Washington should also be developed. Ongoing

research (Allen and Brewer 1985) and a SOMA

monitoring program (Carey and Ruggiero 1985), if

continued, will provide the necessary regional ,i,

information. Research on California spotted owls

in the Sierra Nevada must continue if reasonable

management recommendations are to be made for the

apparently migratory populations there.

CONCLUSION

When the results of recent and ongoing studies

are published, the information on the habitat

requirements of northern spotted owls should be

sufficient for management purposes. More

definitive information on what constitutes the

size of a viable population of northern spotted

owls, however, will be available in the future

once a theoretical framework for defining

viability is developed. But it seems likely that

no fewer than 1,000 pairs of adults will be

required. Recent studies of juvenile dispersal

suggest the present guidelines for distributing

SOMAs should be maintained. It is unlikely that

more definitive information on distribution of

SOMAs can be gained through dispersal studies.

The major information gap is how well present

management is working. Monitoring will be F

essential for effective spotted owl management.

Long-term studies of spotted owls will allow

development of models of viable populations. The ,‘s

data from these studies will however, be of

limited use to managers because most decisions on

the retention of old-growth and mature forests

will be made before the results of such studies

will be known.

Other studies will be useful. Studies on how to

silviculturally create old growth or how to speed

forest development will provide the information

needed to replace old growth as it ages into

climax forest. Studies of interactions between

spotted owls and barred owls could add another

dimension to the concept of viability. As with

most wildlife, there are numerous aspects of

biology that could be studied but that have no

apparent, immediate management application. Such

basic knowledge enhances management in the long

term.

ACKNOWLEDGMENTS

I thank L. Brewer, G. Cooper, H. Black, Jr., H.

Salwasser, K. Horn, B. Marcot. E. Forsman. R. B

Gutiérrez, L. Ruggiero, E. Meslow, and G. Miller

for their careful reviews of an earlier draft of

this paper.

&

110
LITERATURE CITED

Allen, Harriet; Brewer, Larry W. A review of

current northern spotted owl (Strix occidentalis

caurina) research in Washington State. In: - -

Gutiérrez Ralph J.; Carey, Andrew B., tech.

eds. Ecology and management of the spotted owl

in the Pacific Northwes . Gen. Tech. Rep.

PNW-185. Portland, OR: U.S. Department of

Agriculture, Forest Service, Pacific Northwest

Forest and Range Experiment Station; 1985:

55-57.

Barrowclough. George F.; Coats, Sadie L. The

demography and population genetics of owls,

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114
INFORMATION AND RESEARCH NEEDS FOR SPOTTED OWL MANAGEMENT

R. J. Gutiérrez

ABSTRACT : The information and research needs for spotted owl management

-are presented. The following priority list for research is given with the

understanding that research needs may vary among USDA Forest Service

regions and that many research topics could effectively be coordinated or

conducted together. Research and information are needed on: (1) population dynamics, (2) major prey ecology, (3) habitat requirements,

(4) juvenile dispersal, (5) effects of habitat modification on spotted

owls, (6) inventory and monitoring, and (7) owl genetics.

The National Forest Management Act of 1976 (U.S.

Laws, Statutes, etc. 1976) requires the USDA

Forest Service to develop Land Management Plans

(LMPs) for each National Forest. These plans will

contain spotted owl (Strix occidentalis), management plans (SOMPs). The Forest Service is funding

several studies to provide-information on the

basic ecology of the northern spotted owl (S. o.

caurina) to help formulate SOMPs within the general

LMPS. Because these LMPs will be completed within

1-2 years and then be subject to review and

revision in 5-10 years, it is important that

research continues on the northern spotted owl. In

this paper I suggest areas of spotted owl research

that will provide much of the information needed to

adequately review and revise the Forest Service's

SOMPS .

I believe that there are some areas of spotted owl

ecology that need immediate research attention. I

present in this paper a list of research needs

that is the result of my personal experience with

spotted owls, the suggestions of this symposium's

participants, and suggestions from other spotted

owl research biologists. In addition, my list is

R. J. Gutiérrez is an associate professor of wildlife management and chairman of the Department of

Wildlife Management, Humboldt State University,

Arcata, Calif.

strongly influenced by discussions with Cameron

Barrows, Eric Forsman, Gordon Gould, Stephen

Laymon, Charles Sisco, and David Solis during an

informal spotted owl workshop at Arcata, California, April 6-7, 1983. The responsibility for

developing the following list, however, is my

OWn.

SPOTTED OWL RESEARCH NEEDS :

The following suggested areas of spotted owl

research are listed in my priority order. Clearly,

several different research investigations may

continue concurrently. It is my intention only

to suggest areas of research that will provide

critically lacking information on the spotted owl.

I further encourage all research on the spotted

owl to continue and to be shared among all

interested persons.

1. Demography: Only the work of Forsman and

others (1984) presents any substantive data on

population biology. Yet it is clear from

Barrowclough and Coats (1985) that demographic

studies should be considered a top priority.

Such information as age at first reproduction,

life span, reproductive potential, and adult and

juvenile survivorship will be needed to construct

models sufficient to predict effective population

size. This information will also be critical for

evaluating the impact of environmental change on

the species (Shaffer 1985).

115
To my knowledge the only study currently in

progress

 on

demography is in northwestern

California Spotted owl monitoring in the

National Forests of Washington State will also be

a source of demographic data by observing changes

in occupied territories (Allen and Brewer 1985,

Carey and Ruggiero 1985). I suggest that most of

these studies be replicated to assess geographic

variation within northern spotted owl populations

and among other spotted owl subspecies. It is

apparent from other studies that there is

geographic variation within aspects (for example,

food habits) of their natural history (Gutiérrez

1985).

2. Major prey ecology: The ecology of the major

prey of the spotted owl is not well understood yet

prey relationships may be a major reason for the

birds dependence on large areas of old growth

(Gutiérrez 1985). Barrows (1985) also points out

the potential relationship between owl breeding

success and the proportion of large prey in their

diet. Thus, it seems that both the flying

squirrel (Glaucomys sabrinus) and wood rat

(Neotoma sp.) warrant investigation.

Several studies are assessing the status of these

animals in old growth (Raphael and Barrett 1984,

Ruggiero and Carey 1984). These studies are not

designed, however, to provide the most needed

information on these animal's population dynamics,

distribution, density, and geographic variation in

abundance and reproductive success within known

spotted owl territories. The study of spotted owl

prey could be effectively coordinated with owl

demographic studies. This could be accomplished

through monitoring prey populations within known

spotted owl territories. Southern (1970)

successfully used this study design with tawny

owls (Strix aluco). -

Throughout this discussion I will not predict the

cost or the time required to conduct these

studies. The cost and time necessary to effect

these studies will depend on the logistical

constraints of terrain, the level of statistical

precision required, and the type of research

investigation (that is, population dynamics vs.

habitat analysis).

Funding considerations and decisions should be

made using advice from people who know the terrain

and the logistical problems of sampling within a

particular area.

3. Habitat requirements: The specific characteristics of habitat used by and available to

spotted owls are not identified for all major

areas of the owl's range. Solis (1983) provides

data for northwestern California. Laymon (1985)

will provide specific habitat characteristics for

the northern Sierra Nevada. Yet data from mesic

Oregon and Washington, arid Washington, and the

1/Study in progress , Alan Franklin and others, -

2'Study in progress, William LaHaye, Wildlife

Wildlife Management Department, Humboldt State Management Department, Humboldt State UniverUniversity,. Arcata, Calif. sity, Arcata, Calif.

disjunct populations of S. o. caurina in Mendocino, Napa, and Marin Counties of California are

not available. In addition, the relationship

among home range size, habitat dispersion, habitat

quality and reproduction is not well understood.

Habitat models are as yet lacking for the spotted 3

owl. A U.S. Department of the Interior, Fish and

Wildlife Service, Habitat Evaluation Procedure

type Habitat Suitability Index Model is being

developed by Salwasser and Laymon (in press). In -9

addition a model for predicting suitab

2/

e nesting

habitat is being developed by LaHaye.-

One aspect of habitat research that is very

important (when trying to predict the impact of

management scenarios) is quantifying the total

available habitat for spotted owls. There are no

published accounts that have assessed the total

amount, patch size, or distribution of suitable

spotted owl habitat in the Pacific Northwest.

Remote sensing technology does exist for

conducting such a study.

4. Juvenile dispersal: The pattern of juvenile

dispersal and the success of owl dispersers are

still important questions to resolve. Dispersal

studies, however, are expensive research considering the resultant data. At this time I feel it

is important that the study of Miller and Meslow

(1985) continue for its final year. Barrowclough

and Coats (1985) point out the importance of

juvenile dispersal for estimating effective

population size.

In addition to the study of Miller and Meslow -2

(1985), Laymon (1985) is completing a limited

study of juvenile dispersal in the Sierra Nevada

in California. His studies will provide useful CL

comparative dispersal data. &

5. Effects of habitat modification on spotted

owls : Much timber harvesting is occurring in

known spotted owl habitat. There is ample

opportunity to study the impact of timber

harvesting on spotted owl reproductive, foraging,

and habitat use in National Forests. KnudsenVandenberg Funds can be used for monitoring wildlife affected by a specific timber harvest.

Within a region of the Forest Service or the

Bureau of Land Management a sufficient owl sample

size could be gained through regional cooperation

and planning to study the impact of logging on

resident owls.

Controlled experiments on the effects of timber

harvesting will be more difficult to execute

given the nature of commercial timber harvesting

in the Pacific Northwest and the number of owl

sites needed to gain a high level of statistical

precision. Thus far, only anecdotal data has

been gathered on the effects of timber

116
harvesting on owls3/ (for example, Forsman and

others 1984, Solis 1983).

6. Inventory and monitoring: The Forest Service,

Bureau of Land Management, and various State wildlife agencies have all conducted some spotted owl

inventories. The efficiency of these efforts,

however, has never been assessed. I believe owl

populations were probably underestimated. Inventory was done through calling surveys, and response

rates during these surveys may have been affected

by time of day or year, by temperature, by

reproductive condition of the owl, by territorial

status of the bird, by individual variation in

owl response rates, and by the number of calling

episodes within an area. If spotted owl numbers

have been underestimated, then the magnitude of

the impact on regional populations of owls would

be greater than previously anticipated by spotted

owl management schemes.

Monitoring of spotted owl territory occupancy rates

should be addressed to predict the effectiveness

of the spotted owl management plans of the Forest

Service and Bureau of Land Management (Carey and

Ruggiero 1985). Allen and Brewer (1985) are

currently monitoring spotted owl territories in

Washington. Some of these monitoring studies

could be conducted in concert with studies of

population dynamics.

7. Owl genetics: Genetic variability in spotted

owls or between spotted owl demes has never been

investigated. This information may be important

for constructing models of population viability

and determining genetic relationships among

spotted owl populations. These investigations

could be conducted as part of larger studies

(Barrowclough and Coats 1985). Regional

coordination would be helpful.

ADDITIONAL SPOTTED OWL RESEARCH PROGRAMS

In this section I will mention several notable

research programs that have not drawn the same

attention as the Oregon and Northwestern

California studies. I mention these to facilitate communication among persons interested in

spotted owls. The first is the long-term

investigation of Cameron Barrows at the North

Coast Preserve, Branscomb, California. Barrows is

continuing his prey studies presented elsewhere in

this symposium (Barrows 1985) and is monitoring

the long-term reproductive effort of a few

selected pairs of spotted owls. Another research

effort is being conducted in Washington by Harriet

Allen and Larry Brewer of the Washington Department

of Game. Additional studies by Allen and Brewer

(1985) and Barrows (1985) are discussed above or

elsewhere in this symposium (Allen and Brewer 1985,

Barrows 1985). Allen and Brewer are also investigating a very important aspect of spotted owl

3/Unpublished data on file with R. J. Gutiérrez,

Wildlife Management Department, Humboldt State

University, Arcata, Calif.

biology: competition and interaction between

spotted owls-and barred owls (Strix varia). In

addition. the Pacific Northwest Region (USDA

Forest Service) is monitoring the implementation

of their spotted owl management plan. This

latter investigation is headed by Bruce Marcot.

Efforts are being made to design, to implement,

and to coordinate monitoring of spotted owl

management on Federal lands in the Pacific Northwest through a Federal interagency committee

under the auspices of the USDA Forest

Old-Growth Wildlife Habitat Program.4/

Service's

This brief outline of research needs and research

in progress has been presented to encourage

spotted owl research in areas for which management

agencies have specific information needs. The

Old-Growth Wildlife Habitat Program of the USDA

Forest Service, Pacific Northwest Range and

Experiment Station, Olympia, Washington, has been

serving as a clearing-house for west coast

spotted owl studies. Investigators are encouraged

to coordinate their efforts with that program.

LITERATURE CITED

Allen, Harriet; Brewer, Larry W. A review of

current northern spotted owl (Strix occidentalis

caurina) research in Washington State. In:

Gutiérrez, Ralph J.; Carey, Andrew B., tech.

eds. Ecology and management of the spotted owl

in the Pacific Northwest. Gen. Tech. Rep.

PNW-185. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest

Forest and Range Experiment Station; 1985:

55-57.

Barrowclough, George F.; Coats, Sadie, The

demography and population genetics of owls,

with special reference to the conservation of

the spotted owl (Strix occidentalis). In:

Gutiérrez, Ralph J.; Carey, Andrew B., tech.

eds. Ecology and management of the spotted owl

in the Pacific Northwest. Gen. Tech. Rep.

PNW-185. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest

Forest and Range Experiment Station; 1985:

74-85.

Barrows, Cameron W. Breeding success relative to

fluctuations in diet for spotted owls in

California. In: Gutiérrez, Ralph J.; Carey,

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118
ENGLISH AND METRIC EQUIVALENTS

Metric

1 inch = 25 millimeters

1 inch = 2.5 centimeters

1 foot = 30.5 centimeters

1 mile = 1.6 kilometers

1 ounce = 28 grams

1 pound = 453.6 grams

1 ton = 0.907 metric ton

1 acre = 0.40 hectare

o

F = (9/5 oC) + 32

English

1 millimeter = 0.039 inch

1 centimeter = 0.39 inch

1 meter = 39.37 inches or 3.28 feet

1 kilometer - 0.62 mile

1 gram = 0.0353 ounce

1 kilogram = 2.2045 pounds

1 metric ton = 1.02 tons

1 hectare = 2.47 acres

o

C = (OF - 32)/1.8

119
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