Biological Report 82(10.90)

May 1985

L brary

N' ttonal Wetlan: s Pe earch Center

t: . • r Ali ,,' ..u :~udd!P. >:lcNlce

7 0 Cajundomc Bouleva rd

Laf ye leoL.a. 70506

HABITAT SUITABILITY INDEX MODELS:

EASTERN BROWN PELICAN

and Wildlife Service

SK

36 1

. U54

no . 82 -

10 .90

Department of the Interior
This model i de igned to be u ed by the Division of Ecological e ices in

co junction 'th the Habitat E a1 ation Proc ur •

This is one of the f t reports to pu lished in the n "Biological

port e ies. This technical report s rf es , published b-y the Research aM

De elopment branch of the U.. Fi h and Wildlife Service, r place the

FW lOB n ser; s publi hed from 1976 to September 1 4. The Biological eport

series is de igned for the rapid publication of reports with n application

orientation, and it continues the fo us of the FWS/OBS serie on resourc

management isSues and fish and wildlife need •
MODEL EVALUATION FORM

Habitat models are designed for a wide variety of planning applications

where habitat information is an important consideration in the decision

process. It is impossible, however, to develop a model that performs equally

well in all situations. Each model is published individually to facilitate

updating and reprinting as new information becomes available. Assistance from

users and researchers is an important part of the model improvement process.

Please complete this form following application or review of the model. Feel

free to include additional information that may be of use to either a model

developer or model user. We also would appreciate information on model

testing, modification, and application, as well as copies of modified models

or test results. Please return this form to the following address.

National Coastal Ecosystems Team

U.S. Fish and Wildlife Service

1010 Gause Boulevard

Slidell, LA 70458

Thank you for your assistance.

Species _ Geographic

Location------------------------------- Habitat or Cover Type(s )------------------------------------ Type of Application: Impact Analysis__Management Action Analysis~ _

Baseline Other---------------------------- Variables Measured or Evaluated-----------------------

Was the species infonnation useful and accurate? Yes No

If not, what corrections or improvements are needed?-----------
Were the variables and curves clearly defined and useful? Yes No

If not, how were or could they be improved?---------------

Were the techniques suggested for collection of field data:

Appropriate?

Clearly defined?

Easily applied?

Yes

Yes--

Yes--

No

No--

No--

If not, what other data collection techniques are needed? _

Were the model equations logical?

Appropriate?

Yes No

Yes-- No--

How were or could they be improved? _

Other suggesti ons for modi ficati on or improvement (attach curves, equati ons ,

graphs, or other appropriate information)----------------

Additional references or information that should be included in the model:

Model Evaluator or Reviewer ~Date __

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Telephone Number Comm:-------------------- FTS _
Biological Report 82(10.90)

May 1985

HABITAT SUITABILITY INDEX MODELS: EASTERN BROWN PELICAN

by

Terrence M. Hingtgen

Rosemarie Mulholland

Alexander V. Zale

Florida Cooperative Fish and Wildlife Research Unit

School of Forest Resources and Conservation

117 Newins~Ziegler Hall

University of Florida

Gainesville, FL 32611

Project Officer

Carroll L. Cordes

National Coastal Ecosystems Team

U.S. Fish and Wildlife Service

1010 Gause Boulevard

Slidell, LA 70458

Performed for

National Coastal Ecosystems Team

Division of Biological Services

Research and Development

Fish and Wildlife Service

U.S. Department of the Interior

Washington, DC 20240
This report should be cited as:

Hingtgen, T. M., R. Mulholland, and A. V. Zale. 1985. Habitat suitability

index models: eastern brown pelican. U.S. Fish Wildl. Servo Biol. Rep.

82 (10.90) • 20 pp.
PREFACE

The eastern brown pelican habitat suitability index (HSI) model is

intended for use in the habitat evaluation procedures (HEP) developed by the

U.S. Fish and Wildlife Service (1980) for impact assessment and habitat

management. The model was developed from a review and synthesis of existing

information and is scaled to produce an index of habitat suitability between 0

(unsuitable habitat) and 1 (optimally suitable habitat). Assumptions involved

in developing the HSI model and guidelines for model applications, including

methods for measuring model variables, are described.

This model is a hypothesis of species-habitat relationships, not a

statement of proven cause and effect. The model has not been field-tested.

For this reason, the U.S. Fish and Wildlife Service encourages model users to

convey comments and suggestions that may help increase the utility and effectiveness of this habitat-based approach to fish and wildlife management.

Please send any comments and suggestions you may have on the HSI model to the

following address.

National Coastal Ecosystems Team

U.S. Fish and Wildlife Service

1010 Gause Boulevard

Slidell, LA 70458

iii

PREFACE . . • .

ACKNOWLEDGMENTS . . . . . .

CONTENTS

iii

vi

INTRODUCTION . . • . .

Distribution ...•..

Life History Overview ....•.

SPECIFIC HABITAT REQUIREMENTS . Food . . . . . . . . . . . • .

Wa ter . . . . . . . . . . . . . . . . • • • .

Nesting, Loafing, and Roosting Cover,.

Special Considerations • • .

HABITAT SUITABILITY INDEX (HSI) MODEL •.

Model Applicability . . • . • . . • • . •..

Model Description •••...•......•.•

Suitability Index (SI) Graphs for Model Variables

Component Index (CI) Equation and HSI Determination

Field Use of the Model . • . . • • . . ••.

Interpreting Model Output

REFERENCES

v

1

2

2

3

3

4

4

6

7

7

8

10

12

13

13

15
ACKNOWLEDGMENTS

Development of the habitat suitability index model for the eastern brown

pelican was reviewed and constructively criticized by Erwin E. Klaas and Jaime

A. Collazo, Iowa Cooperative Wildlife Research Unit, Iowa State University,

Ames; Steven A. Nesbitt, Florida Game and Fresh Water Fish Commission, Wildlife Research Laboratory, Gainesville; Ralph W. Schreiber, Museum of Natural

History, Los Angeles, California; David J. Wesley, Endangered Species Field

Office, U.S. Fish and Wildlife Service (FWS), Jacksonville, Florida; Lovett E.

Williams, Jr., Florida Game and Fresh Water Fish Commission, Wildlife Research

Laboratory, Gainesville; and Don A. Wood, Florida Game and Fresh Water Fish

Commission, Tallahassee. Thorough evaluations of model structure and functional relationships were provided by personnel of the FWS National Coastal

Ecosystems Team (NCET). Supportive narrative and model reviews also were

provided by Regional personnel of the FWS. Funding for model development and

publication was provided by the FWS. The cover illustration was prepared by

Patrick J. Lynch.

vi
EASTERN BROWN PELICAN (Pelecanus occidentalis carolinensis)

INTRODUCTION

Brown pelicans (Pelecanus occidental is) are large marine birds (3.5 kg or

7.7 lb) with a wingspan of 2 m (6.6 ft) that prey on fish by plunge-diving.

Two brown pelican subspecies occur along coastal regions of the continental

United States (Wetmore 1945). The eastern brown pelican (P. o. carolinensis)

is found along the Atlantic coast from North Carolina to Floriaa and along the entire gulf coast to northern South America; it also ranges along the Pacific

coast from southern Mexico to Columbia. The California brown pelican (P. o.

californicus) is found along the Pacific coast from Washington south-into

Mexico. The eastern subspecies is smaller, with a wingchord averaging 25 mm

(l inch) shorter (526 mm or 21 inches total length) than the California

subspecies, and has lighter breeding plumage on the hindneck (Wetmore 1945).

This habitat suitability index model applies only to the eastern brown

pelican.

Dramatic declines in brown pelican populations have been observed twice

during this century (King et ale 1977a). In the 1930's, brown pelicans were

destroyed by fishermen in Texas and Louisiana because of presumed competition

for commercial fish (Gustafson et ale 1939). Food habit studies since then

have shown that commercially important fish species comprise only 1% to 10% of

the brown pelican diet (Palmer 1962); consequently, these birds probably have

little impact on the commercial fishery (see Anderson et ale 1980).

The decline in breeding populations in Texas and South Carolina has been

attributed to disease, inclement weather, and pollution (Blus 1970; Schreiber

and Risebrough 1972; King et ale 1977b). Organochlorines in the food chain

have been implicated as the cause of eggshell thinning and lowered reproductive success since the late 1950's (Mount and Putnicki 1966; Anderson et ale

1975; Nesbitt et ale 1978; Blus et ale 1979a; Mendenhall and Prouty 1979; Blus

1982). The western subspecies of brown pelican experienced complete reproduc- tive failure in California in 1969 (Risebrough et ale 1971), and the eastern

subspecies was extirpated in Louisiana in the late 1950 ls and early 1960's

(King et ale 1977a). Both subspecies were placed on the Federal Endangered Species List in 1970 (USNFWL 1980). A breeding population of eastern brown

pelicans was reintroduced into Louisiana from Florida (Williams and Joanen

1974; Nesbitt et ale 1978). Eastern brown pel ican populations have become

stable or have even increased in the Southeastern United States under protection. The subspecies and its habitats in North and South Carolina, Georgia, Florida, and Alabama were recently removed from Endangered Species Act protection (U.S. Fish and Wildlife Service 1985).

1
Distribution

In the United States, the eastern brown pelican breeding range includes

the Atlantic coast of North Carolina, South Carolina, and Florida and the gulf

coast of Florida, Alabama, Louisiana, and Texas (Palmer 1962).

Along the Atlantic Coast in North Carolina, the brown pelican nesting

population has been divided between Shell Castle and North Rock Islands or, in

some years, between Beacon Island and Cape Fear River spoil islands (Williams

1979; Clapp et ale 1982; Donald McCrimmon, Cornell University Laboratory of

Ornithology; pers. comm.). Two colonies occur in South Carolina, one on

Deveaux Bank and one at Cape Romain National Wildlife Refuge (Mendenhall and

Prouty 1979). On the Atlantic coast of Florida, the species nests from Port

Orange in Volusia County to the Florida Keys (Nesbitt et ale 1982). Brown

pelicans nest along the gulf coast of Florida from Cedar Key- in Levy County south to the Florida Keys; exceptions are a colony in Bay County near Panama

City and a former colony near Port St. Joe (Florida Game and Fresh Water Fish

Commission 1984). Brown pelican nesting colonies in Florida have been mapped

and numbered by Williams (1979). Breeding populations on Florida's Atlantic

and gulf coasts tend to remain separate (Schreiber 1976b). Additional

colonies along the gulf coast include one in Mobile Bay, Alabama, and two

restored colonies in Louisiana, one on Queen Bess Island near Grand Terre, and

one on an island near the northern Chandeleur Islands. Texas recently has had

four colony sites from Matagorda Bay south to Corpus Christi Bay (Texas Parks

and Wildlife Department 1983).

In 1983, at least 1,382 pairs of eastern brown pelicans bred in North

Carolina (McCrimmon, pers. comm.), 4,919 pairs in South Carolina (Phillip Wilkinson, South Carolina Wildlife and Marine Resources Department; pers.

comm.), 6,980 pairs in Florida (Florida Game and Fresh Water Fish Commission

1984), at least 500 pairs in Louisiana (Larry McNease, Louisiana Department of

Wildlife and Fisheries; pers. comm.), and 96 pairs in Texas (Texas Parks and

Wildlife Department 1983).

Locati ons of peak concentrati ons of nonbreeding eastern brown pel i cans

and breeding colony sites have been listed for the Atlantic (Osborn and Custer

1978; Portnoy et ale 1981; Nesbitt et ale 1982) and gulf coasts (Williams

1979; Clapp et al. 1982; Nesbitt et ale 1982; Texas Colonial Waterbird Society

1982; Keller et ale 1984).

Life History Overview

Eastern brown pelicans usually begin to breed when they are 3 to 5 years

old (Williams and Joanen 1974; Blus and Keahey 1978); their longevity

approaches 20 years (Clapp et al. 1982). They nest in colonies of 10 to 1,500

pairs, though colonies usually average several hundred pairs (Schreiber 1978).

The nesting season can vary by more than a month from year to year and probably is related to patterns of unseasonably high or low temperatures (Schreiber 1980a). Brown pelicans often begin nesting in February on Florida's west

coast and in December on the east coast and Flori da Keys. Nesti ng in North

and South Carolina and in Texas often begins in March (Schreiber 1980a).

2
Transplanted colony offspring in Louisiana have retained the nesting season

timing of the source population from Florida. They nest several months

earlier than the native population that was extirpated in Louisiana (Portnoy

1977).

Although most eggs are laid during the season's first 3 months, egglaying can span 6 months with both fledglings and eggs present in mid- season

(Schreiber 1979). The usual clutch size is three eggs. Production of young

fledglings requires about 18 weeks, including 1 to 2 weeks for nest building.

Pelicans begin a 3D-day incubation period after laying the first egg, resulting in asynchronous hatching (Schreiber 1979) and a greater chance of fledging

for the first hatchling (Schreiber 1976a). Both sexes attend the altricial

young for 10 to 12 weeks (Schreiber 1979). Breeding success is dependent upon

the foraging success of the adults and varies greatly from year to year

(Schreiber 1979; Anderson et al . 1982). Factors, in addition to starvation,

that cause reduced breeding success include flooding of nests, nest desertion

due to heavy tick infestation, egg breakage caused by adult birds' flushing in

response to human di sturbance, and predati on of disturbed, unattended nests

(reviewed by Clapp et al . 1982). Survival of nestlings and fledglings, not

clutch size or hatching success, is the major source of variation in annual

productivity of brown pelicans. Highest nestling mortality occurs during the

first 30 days after hatching (Schreiber 1979). Captive brown pelicans have

re-layed up to three times in a season and within 1 to 3 months after the

previous loss. Schreiber (1979) found that re-laying occurred in as many as

26% (N=23) of nests in wild colonies. Later attempts had lower hatching

success but were more likely to fledge hatchlings (85% success, N=39) than

nests with only initial clutches (52% success, N=61D) (Schreiber 1979).

Postfledging mortality for the first year averages 69% to 76% and then

declines to an annual mortality of 16% as the birds become more proficient at

foraging (Henny 1972; Schreiber 1976b, 1978). After the nesting season, birds

along the Atlantic coast disperse to the south along the Florida east coast to

the Keys (Schrei ber 1976b). Pel i cans on the gulf coast also disperse southward, and many probably winter south of the United States (Schreiber and

Schreiber 1983).

SPECIFIC HABITAT REQUIREMENTS

Food

Eastern brown pelican food habits vary within its breeding range. In

South Carolina, brown pelicans feed almost exclusively on young Atlantic

menhaden (Brevoortia tyrannus) found in coastal estuaries (Blus et al. 1979b).

In Louisiana and Texas, 90% to 95% of the diet (weight or volume not specified) consists of gulf menhaden (B. patronus), mullet (MU9V sp.), and other

species not considered sportfish [pearson 1921; Krantz 1968. Fogarty et al.

(1981) found that regurgitated food boluses of Florida nestlings consisted of

14% menhaden by weight, with the remainder comprising 28% Atlantic threadfin

(Polydactylus octonemus), 17% mullet, 11% spot (Leiostomus xanthurus), and 8%

pinfish (Lagodon rhomboides). Adults must supply about 57 kg (125 16) of fish

3
to each young before fledging and require about 90 kg (198 lb) for themselves

during nesting (Schreiber 1976a, 1982). Indirect evidence from parasitological studies indicates that nestlings are fed progressively larger fish of

greater diversity as they grow older and that fledglings along the Florida

coast are heavily dependent on mullet while learning to feed (Humphrey et al.

1978).

Brown pelicans plunge-dive from heights of up to 20 m (66 ft) to capture

prey with their bill and pouch (Schreiber et ale 1975). Percentage estimates

of successful plunge-dives have ranged from 30% (Gunter 1958) to 84% (Schnell

et ale 1983). The lowest estimate includes data from immatures, which tend to

be less successful (10% to 20% less) than adults (Orians 1969; Schnell et ale

1983). Pelicans usually capture prey items less than 25 cm (10 inches) long,

and most captures occur in the top 1 m (3.3 ft) of water (Krantz 1968; Schreiber 1979; Schnell et ale 1983). These birds are not suited-for underwater

pursuit of prey (Sivak et ale 1977) but can capture fish by scooping them up while swimming at the surface (Dinsmore 1974; Rodgers 1978). Brown pelicans

will scavenge offal thrown from boats or fishing piers (Sefton 1950; Schreiber

1978).

Eastern brown pelicans forage primarily in shallow estuarine waters

(Schreiber 1978) and in marine waters within 32 km (20 mi) of shore (Williams

1979). The western subspecies may feed regularly up to 175 km (105 mi)

offshore and 75 km (45 mi) from the nearest island (Briggs et al. 1981).

California brown pelicans may forage at distances up to 75 km (45 mi) from

their nesting colonies (Shannon 1933; Clapp et ale 1982), although most

foraging occurs within 20 km (12 mi) of the nest site (Briggs et ale 1981).

Water

The dietary water requirements of brown pelicans can be satisfied by

consumption of seawater (Schmidt-Nielsen and Fange 1958).

Nesting, Loafing, and Roosting Cover

Eastern brown pelican nesting colonies occur on coastal islands small

enough to be free from human habitation and recreation and far enough from the

mainland to be inaccessible to potential mammalian predators (Schreiber 1979;

Williams 1979). Nesting colonies may abandon islands accessible to mammalian

predators (Schreiber 1979).

Brown pelicans use both natural and man-made islands for nesting. In

Florida, 20% of the breeding population nests on dredged-material islands

(Schreiber and Schreiber 1978), reaching densities of 105 nests/ha (42

nests/acre) (Maxwell and Kale 1974). In addition, birds make extensive use of

undisturbed dredged-material islands and sandbars for loafing and roosting

(Schreiber and Schreiber 1982). Natural islands may be avoided because of

their use by humans for recreation. Colony size (number of nests) is related

to the amount of suitable nesting habitat. In areas where there are fewer

islands with suitable nesting habitat, the average number of nests per colony

is larger (Williams and Martin 1968).

4
Brown pelicans in the Carolinas and Texas nest on the ground or in small

shrubs (Mendenhall and Prouty 1979; Clapp et al. 1982). In Louisiana, nests

are built in black mangroves (Avicennia ,erminans) and on the ground (Blus et

al . 1979a). Nests in Florida are usua ly constructed on open branches of

mangrove trees (A. Serminans, Rhizophora mangle, La~uncularia racemosa) 0.6 to

10 m (2 to 35 ftT a ove the ground, with the exceptlon of one colony along the

east coast consisting entirely of ground nests (Williams and Martin 1968;

Schreiber 1978). Along the Florida gulf coast, nests are occasionally constructed in southern redcedar (Juniperus silicicola), redbay (Persea

borbonia), seagrape (Coccoloba uvifera), and 1ive oak (Quercus virginiana)

(Williams and Martin 1970; Lovett E. Williams, Jr., Florida Game and Fresh

Water Fish Commission; pers. comm.).

Brown pelicans nesting in trees are less vulnerable to flooding, human

disturbance, and opportunistic predators than those nesting on the ground

(Schreiber 1979; Lovett E. Williams, Jr., pers. comm.). When ground nesting

occurs within the mangrove range, it is often on deteriorating islands where

birds previously nested in trees (Schreiber and Schreiber 1978). Island

elevation is important for nesting colonies outside the range of mangroves,

where nesting is usually on the ground or in small shrubs. Nests on a colony·s periphery are often flooded (Blus and Keahey 1978; Mendenhall and Prouty

1979). Potential nesting cover must be able to support a nest from 0.6 m (2

ft) to 10.7 m (35 ft) above the ground or high tide (Schreiber 1978).

Suitable branches for perching are important in nest site selection in

mangroves (Schreiber 1977). Branches used for perching are usually within 1.2

m (3.9 ft) of the nest. Mangrove branches are also used in nest construction

and are usually gathered from trees away from the nesting site. This results

in areas of defoliation away from the colony but on the same island (Schreiber

1977). Distances between nests in mangroves are not less than 103 m (4.3 ft)

or the distance neighboring pairs can reach while on the nest (Schreiber

1977). The number of active nests in colonies reported to the Colonial Bird

Regi ster (unpub1i shed data) averaged 204 ± 32 nests per colony (Mean ± SE,

N=99).

In Florida, Schreiber and Schreiber (1982) found that nesting adults may

spend all of their nonforaging time on the colony island (Schreiber and

Schreiber 1982). When not on the nests, they make use of sandbars and spits for loafing and roosting. These areas are essential drying sites for pelicans

that become waterlogged after more than an hour on the water (Schreiber and

Schreiber 1982). Older nestlings use vegetation and rocks on the island for

shade during the hottest part of the day (Bartholomew and Dawson 1954), and

new fled~lings use the island for loafing and roosting (Schreiber and Schreiber 1982). Sandbars and spits are especially important to new fledglings that

have not developed the coordination necessary to land on branches.

Although brown pelicans tend to use the same colony islands from one year

to the next, factors such as proximi ty to food resources, human disturbance,

predation, ectoparasites (see Special Considerations), and defoliation due to

nesting activities may cause birds to shift breeding sites on a particular

5
island as well as between islands from year to year (Williams and Martin 1968;

Maxwell and Kale 1974; Schreiber and Schreiber 1982; Anderson and Gress 1983).

Establishment of a new colony on an island is preceded by use of that

island for non-nestin~ activities (Schreiber and Schreiber 1982). Birds first

use an island for loafing during the non-nesting season, then for roosting and

loafing year-round, and then as a colony site. This progression of use may

occur over a 3- to 4-year period (Lovett E. Williams, Jr., pers. comm.).

Whether previous use is a necessary condition for establ ishment of a new

colony has not been determined. Potential nesting habitat previously used for

roosting and loafing is assumed to be more suitable than unused habitat.

Special Considerations

Severa 1 sources of human-i nduced stress can 1imit the producti vity of

brown pelicans. Organochlorines introduced into the food chain result in

eggshell thinning (Blus et al . 1971; Blus et al. 1977; Mendenhall and Prouty

1979). Eggshell thickness was log-linearly related to DOE concentrations in

eggs (Blus et a1. 1972). Fat in starvati on-stressed bi rds contained the

highest levels of pesticide (Thompson et al. 1977). Some California colonies

exposed to DDT-related compounds in food fish at concentrations of 4.3 parts

per million have produced almost no young during the nesting season (Anderson

et al. 1975). Organochlorines, particularly endrin, also have been implicated

in the 1975 die-off of 150 adult birds (40% of the population) in Louisiana

(Blus et al. 1979a).

The principal source of eastern brown pelican nesting failure is direct

and indirect human interference with nesting colonies (Clapp et al , 1982).

California brown pelican productivity (young per nest) may decline 52% to

100% as a result of one disturbance at the beginning of the nesting season

(Anderson and Keith 1980). Eastern brown pelican nests disturbed two or more

times per week have fewer eggs laid and reduced hatching success compared to

nests disturbed once per week (Schreiber 1979). Flushing birds from nests

allows avian predators like the fish crow (Corvus ossifragus) to destroy many

eggs and young (Schreiber and Risebrough 1972). In addition, adults may not

take time to step off the nest before flushing, resulting in crushed or

displaced eggs or young. Nesting brown pelicans become alert to human

presence within 100 m (328 f t ) of the colony (Schreiber 1979), and loafing

pelicans on colony islands prefer sandbars that are undisturbed by human

acti vity.

Brown pelicans often scavenge food from fish-cleaning areas at marinas.

Lincer et al . (1979) suggested that this unusual prey may have higher pesticide levels than the natural prey, which are fish lower in the food chain.

Another hazard around marinas is entanglement in fishing lines, accounting for

the deaths of more than 700 birds annually (Schreiber 1980b).

Oil spill s cause an undetermi ned amount of mortality (Stevenson 1970).

Adul t marta 1i ty may occur at the time of the spi 11 or after resuspens i on of

oil accumulated in sediment (King et al. 1979). Hatching success may be

reduced by oil contamination of eggs. Following an oil spill in North

6
Carolina, Parnell et ale (1983) found that 66% of the oil-contaminated eggs

hatched, compared to 84% of unoiled eggs.

Another 1imiting factor to successful reproduction is ectoparasite load

at the nest site. Excessive tick infestation in nesting areas has been

implicated in the desertion of eggs and young by adult birds in Texas, California, and Peru (King et ale 1977b, 1977c; Duffy 1983). Ticks can number

more than 700 per nest in severe infestations, can carry pathogenic viruses,

and may cause birds to avoid the nesting area the following year.

HABITAT SUITABILITY INDEX (HSI) MODEL

Model Applicability

This model can be used to evaluate estuarine island habitat (Cowardin et

ale 1979), natural islands, and dredge islands within the eastern brown

pelican breeding range (Figure 1). The minimum habitat area required for

breeding has not been established.

Figure 1. Breeding range of the eastern brown pelican and regions (shaded) of

model applicability (Clapp et al. 1982).

7
Season. Eastern brown pelican breeding season can be year-round in

southern Florida but tends to be late winter, spring, and/or early summer at

more northern latitudes. The model should be used to evaluate breeding

habitat at the beginning of the breeding season.

Verification level. The acceptable model output is an index value

between 0.0 and 1.0 that reflects the habitat potential for eastern brown

pelican nesting. A value of 1.0 indicates optimal suitability and 0.0 indicates unsuitability. The model has not been field-tested. Hypothetical data

sets were used to verify that the mode 1 output was reasonable. Revi ewersf

comments have been incorporated, but the authors are responsible for the final

version of this model.

Model Description

Overview. Components of the eastern brown pel ican breeding habitat are

nesting, roosting, loafing, and foraging sites. The quality of feeding sites

around a colony may account for year-to-year variation in colony use and may

limit the use of potential nesting habitat. Although the breeding success of

California brown pelicans is dependent on food resources around their colony islands (Anderson et al. 1982), food distribution has not been incorporated as

a variable in the eastern brown pelican habitat evaluation model because of

lack of knowledge about the seasonal distributions of surface fish schools

(see Schreiber and Schreiber 1983). Nesting, roosting, and loafing sites are

evaluated by measuring habitat variables for the single life requisite of

nesting/loafing cover (Figure 2). Use of this model assumes that the nesting

habitat under evaluation comprises estuarine islands that do not support known

populations of quadruped predators.

Nesting/loafing cover. Habitat variables in the model related to breeding habitat quality of an estuarine island are island surface area, distance

from mainland, distance from human activity centers, and relative coverage of

nesting vegetation.

The island surface area (VI) and its distance from mainland (V2) are

assumed to be indications of its accessibility to quadruped predators.

Islands larger than 8 ha (20 acres) may be able to support resident popula- tions of predators (Landin 1978). Because brown pelicans are colonial nesters

and mean colony size is probably 100 nests or more (Colonial Bird Register,

unpubl ished data), the minimum area of highest suitabil ity is assumed to be 2

ha (5 acres). This includes 1 ha (2.5 acres) of nesting area required by

colonies of about 100 pairs at a density of 105 nests/ha (42 nests/acre), and

1 ha (2.5 acres) for loafing and drying.

Optimal distance from the mainland (V2) is assumed to be 0.4 km (0.25 mi)

or more, and suitability increases to a maximum at that distance (see Lewis

1983). Distance of islands from human activity centers (V 3 ) also influences

habitat quality for nesting brown pelicans. Islands that have permanent human

inhabitants or are visited by humans for recreational or commercial purposes

during the breeding season are less suitable for nesting. Islands that are

at least 100 m (328 f t ) from areas of human activity may be used by brown

pelicans for nesting, but suitability increases with distance to an optimum of

8
Habitat variable

Life

requi site Habitat

VI Island surface area

V2 Distance from mainland

V4 Pelative coverage of

nesting vegetation

------~lNesting/loafing Estuarine (island) HSI

cover

Distance from human

activity center

V

3

Figure 2. Relationships of habitat variables, life requisite, and habitat type in the HSI model for

the eastern brown pelican.
0.4 km (0.25 mi) or more. This distance was chosen because it minimi zes

spurious visits by humans or their domestic animals.

Nesting cover (V,+) is identified differently for Florida, Alabama, and

Louisiana than for Texas and the Carolinas. Where mangroves occur (FL, AL,

LA), tree or shrub nesting is considered optimal for brown pelicans because

nests can be constructed above high tide on low elevation islands, and pelicans are less vulnerable to human disturbance and opportunistic predators.

Eastern brown pelicans nesting outside the mangrove range, including eastern

Texas and the Carolinas, usually nest on the ground or in small shrubs.

Island elevation is important for these colonies. Therefore, island surface

and shrubs that are potential nesting cover must be at least 0.6 m (2 f t )

above high tide. Nesting vegetation covering 50% or more of an island is

considered optimal.

Suitability Index (SI) Graphs for Model Variables

The re 1ati onshi ps between the habitat vari ab1es and breedi ng habitat

suitability for brown pelicans are presented graphically in this section. The

assumptions necessary to construct the model are summarized in Table 1. The

SI values on the ordinate axis range from optimal habitat (1.0) to unsuitable

habitat (0.0).

Habitat Variable Description Suitability Graph

I-

-

. -

E Island surface area 1.0

1) Less than 2 ha

(4.9 acres) )( 0.8

2) 2 to 8 ha (4.9 to CD

19.8 acres) c

- 0.6 3) Greater than 8 ha )i,

(19.8 acres). 5

,g 0.4 as

::

en 0.2

0.0

10

1 2

Class

3
Habitat Variable Description Suitability Graph

E V2 Straight-line distance of 1.0

island from mainland.

)( 0.8

CD

1:J

.5 0.6

>-

.c 0.4 as

:!:

en 0.2

0.0

0.0 0.2 0.4 '0.6 0.8

Distance (krn)

1.0

E V3 Straight-line distance of

island from nearest human

activity center. )( 0.8

CD

1:J

.5 0.6

>- :!:

.-.c 0.4 as

:!:

en 0.2

0.0

0.0 0.2 0.4 0.6 0.8

Distance (km)

1.0 E V4 Relative coverage of nesting vegetation.

Within the range of )( 0.8

mangrove (FL, AL, LA), CD

1:J

relative coverage is .5 0.6 the percentage of the >-

island supporting woody

vegetation 0.6 to 10.7 m .Q 0.4 as

(2 to 35 ft) in height. :!:

Outside this range (NC, en 0.2

SC, TX), relative coverage is the percentage of the 0.0 island surface area at

least 0.6 m (2 ft) in 0 20 40 60 80 100

elevation. %

11
Table 1. Sources of information and assumptions regarding breeding habitat

variables used to calculate the HSI for eastern brown pelicans.

Variable and sources

Landin 1978

Schreiber 1977

Colonial Bird Register,

unpublished data

Schreiber 1979

Buckley and Buckley 1980

Briggs et ale 1981

Williams and Martin 1970

Jehl 1973

Schreiber 1979

Schreiber and Schreiber 1982

Nesbitt et ale 1977

Schreiber 1977, 1978

Blus and Keahey 1978

Schreiber and Schreiber 1978

Blus et ale 1979a

Assumptions

Islands that are 8 ha (20 acres) or

larger are most likely to support

resident populations of quadruped predators. Average colonies require at

least 1.0 ha (2.5 acres) of nesting cover

and a similar size sandy area for drying and loafing.

Colony islands close to mainland are more

accessible to mammalian predators.

Islands that are 0.4 km (0.25 mi) or

more from the mainland are virtually

inaccessible. Island is assumed to be

initially free of quadruped predators.

Brown pelicans respond to human activity within 100 m (330 ft) of nesting colonies.

One disturbance can disrupt production.

Islands that are 0.4 km (0.25 mi) from

the nearest center of human activity have

less chance of being disturbed.

Tree heights of 0.6 to 10.7 m (2 to 35 ft)

are optimal for nesting within the range of

mangroves. Outside that range, ground

nests higher than 0.6 m (2 ft) have a low

risk of flooding.

Component Index (CI) Equation and HSI Determination

Nesting/loafing cover is the only life requisite considered in this

model. Therefore, the HSI value equals the component index (cr) for cover.

We suggest the following equation to obtain the CI and HSI values.

Component

Cover (C)

HSI = C

Equation

(SIV1 X SIV2 X SIV3 X SIV4)1/4

12
The output of the model is demonstrated for hypothetical data in Table 2.

The first data set represents a situation where cover is limiting, while the

second and third data sets represent situations where colonies are more

vulnerable to predation and human disturbance.

Field Use of the Model

Suggested methods for measuring habitat variables are presented in Table

3. These methods were chosen for their efficient use of time and resources.

If neither of these is limiting, methods producing a larger, more comprehensive data base may not only increase the precision of the model but may also

provide information leading to its improvement.

Interpreting Model Output

When areas with similar HSI values are compared, an area previously used

by pelicans for roosting and loafing is more likely to be used for nesting in

the near future than an unused area. As with other HSI models, the HSI value

obtained may have no relationship to nesting population size but indicates the

potential of an area as nesting habitat.

Further studies of brown pelican ecology are necessary to provide information for model improvement. Especially needed are studies on nesting colony distribution relative to food fish distribution in surface waters, the effect

of vegetation characteristics on nesting success, and the development of new

colonies. Modifications and improvements should be incorporated as new data

are collected.

Table 2. Model output of the component index (CI) and habitat suitabil ity

index (HSI) for three hypothetical data sets with their corresponding

sui tabi 1ity index (SI) values.

Model Data set 1 Data set 2 Data set 3

component Data sl Data 51 Data 51

VI 2 ha 1. 00 17 ha 0.40 4 ha 1. 00

V2 0.5 km 1. 00 0.1 km 0.25 0.4 km 1. 00

V3 0.5 km 1. 00 0.1 km 0 0.2 km 0.33

V4 40% 0.80 50% 1. 00 25% 0.50

C 0.95 0 0.64

HSI 0.95 0 0.64

13
Table 3. Suggested techniques for measuring breeding habitat variables for

the brown pelican HSI model.

Habitat variable

VI Island surface

area

V2 Distance from

mainland

V3 Distance from

nearest human

activity center

V4 Relative cover

of nesting

vegetation

Technique

Measure area of the island on a topographic map or

aerial photo taken at high tide.

Measure straight-line distance from mainland shore to

island shore at low tide.

Measure straight-line distance from closest area of

any center of human activity to colony island. Identify

the closest area of current human activity or projected

human activity during the nesting season, whichever is

the shorter distance.

Use aerial photos and topographic maps of estuarine

islands to measure coverage of trees and shrubs 0.6 m

(2 ft) to 10.7 m (35 ft) high (FL, AL, LA) or the area

of island surface at least 0.6 m (2 ft) in elevation

(NC, SC, TX). Visit islands to confirm vegetation

physiognomy. Branches should provide nonsagging support

of 6.5 kg (14 lb) (weight of two adults) at least 0.6 m

(2 ft) above the ground.

14
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15
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16
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17
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18
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20
50272 -101

REPORT DOCUMENTATION [_I. R.EPORT ':fO. Report 82{10.90) 1

2

•

J. Rec's»I.nt'. Acc •••lon No.

PAGE ]lologlcal I --I--- 4. Tltlo ond Subtltlo S. Roport ooto

Habi tat Su i tabil ity Index Models: Eastern Brown Pelican May 1985 6.

--~~-

7. Autho,(o) 8. Performln. Or••nlz8tion Rept. No.

T M Hinataen Rosemarie Mulholland. and Alexander V. Zale

9. Performln. O,...nization Name and Addr.ss 10. Project/T••k/Work Unit No.

-~

Florida Cooperative Fish and Wil dl ife Research Uni t

School of Forest Resou rces and Conservation 11. Contr.ctCC) or Grant(G) No.

ll? Newins-Ziegler Hall. University of Florida «»

Gainesville. FL 32611 (G)

12. Spon$orina: Or.8"lz8tlon H.me and Address 13. Type of Report & Period Coyered

National Coastal Ecosystems Team Fish and Wil dl ife Service

Division of Biological Services U.S. Department of Interior

Resea rch and Development Wa shi nqton, DC 20240 -------~--------~

14.

15. Supplementary Notes

16. Abstract (Limit: 200 words)

A review and synthesis of existing information were used to develop a habitat model

for the eastern brown pelican (Pelecanus occidentalis carolinensis). The model is

sea1ed to produce an index of habitat sui tabil i ty between 0 (unsuitable habitat)

and 1.0 (optimal habitat) for coastal areas within the eastern brown pelican's

breeding range. Habitat sui tabi 1i ty indices are designed for use with the Habitat

Eval uati on Procedures previously developed by the U.S. Fish and Wildlife Service.

Guidelines for application of the eastern brown pelican habitat model and techni ques

for measuring model variables are described.

------_. --- --.. -----,-._--------_..._------- 17. Document Analysis 8. Descriptors

Mathematical models

Wildlife

Birds

b. Identifiers/Open-Ended Terms

Habitat Habitat suitability index

Impact assessment Eastern brown pelican

Pelecanus occidentalis carol inensi s

c. eOSATI Field/Group

._-------------~-----.= 1& Ay. ilabillty Statement I 19. Security Class (This Report) 21. No. of Po.e>

Unl imited Uncl assi fi ed 20 ---- ~--- ----- 20. Security Class (This Page) 22. Price

Unclassified

(See ANSI-239.IS)

*U.S. GOVERNMENT PRINTING OFFICE: 1985- 573-260

OPTIONAL FORM 272 (4-77)

(Former-ly NTIS-35)

Department of Commerce
.. .... ...

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*Headquarters. Division of BloiOOic..

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)( E..lem Energy and Land Use Team

u..lown. WV

• Nallonal Co..tal Ecosystems Team Slidell, LA

• Weslern Energy and Land Use Team FI. Collins, CO

• Locations of Regional Offices

REGION 1

Regional Director

U.S. Fish and Wildlife Service

Lloyd Five Hundred Building, Suite 1692

500 N.E. Multnomah Street

Portland, Oregon 97232

REGION 4

Regional Director

U.S. Fish and Wildlife Service

Richard B. Russell Building

75 Spring Street, S.W.

Atlanta, Georgia 30303

I

J- - - - - - -

6 1

,-- ~-

L , --J

I : -~ --- I {

•

REGION 2

Regional Director

U.S. Fish and Wildlife Service

P.O. Box 1306

Albuquerque, New Mexico 87103

REGION S

Regional Director

U.S. Fish and Wildlife Service

One Gateway Center

Newton Corner, Massachusetts 02158

REGION 7

Regional Director

U.S. Fish and Wildlife Service

1011 E. Tudor Road

Anchorage, Alaska 99503

Habitat suitability index roodels. 19518

Hingtgen, Terrence H. SKlil .U54 00.82

IIIII ~~~ll~l~1

. .,'

REGION 3

Regional Director

U;S. Fish and Wildlife Service

Federal Building, Fort Snelling

Twin Cities, Minnesota 55 IJI

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Regional Director

us. Fish and Wildlife Service

P.O. Box 25486

Denver Federal Center

Denver, Colorado 80225
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