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BIOLOGICAL REPORT 82(10.140)

JUNE 1987

HABITAT SUITABILITY INDEX MODELS:

GREATER SANDHILL CRANE

; i 1 .:

L:~h and Wildlife Service i

SK ). Department of the Interior

361

. U54

no . 82 -

10. 140
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. However, it is impossible to develop a model that

performs equally well in all situations. Assistance from users and

researchers is an important part of the model improvement process. Each

model is published individually to facilitate updating and reprinting as

new information becomes available. User feedback on model performance

will assist in improving habitat models for future applications. 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:

Habitat Evaluation Procedures Group

U.S. Fish and Wildlife Service

2627 Redwing Road, Creekside One

Fort Collins, CO 80526-2899

Thank you for your assistance.

Species _

Habitat or Cover Type(s)

Geographic

Location

Type of Application: Impact Analysis Management Action Analysis __ Baseline Other -------------------------

Variables Measured or Evaluated --------------------

Was the species information 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? Yes No

Clearly defined? Yes No

Easily applied? Yes No

If not, what other data collection techniques are needed?

Were the model equations logical? Yes No

Appropriate? Yes No

How were or could they be improved?

Other suggestions for modification or improvement (attach curves,

equations, graphs, or other appropriate information)

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

Model Evaluator or Reviewer Date ------------

Agency _

Address ------------------------------

Telephone Number Comm:----------- FTS _
Biological Report 82(10.140)

June 1987

HABITAT SUITABILITY INDEX MODELS: GREATER SANDHILL CRANE

by

Michael J. Armbruster

National Ecology Center

U.S. Fish and Wildlife Service

Drake Creekside Building One

2627 Redwing Road

Fort Collins, CO 80526-2899

National Ecology Center

Fish and Wildlife Service

U.S. Department of the Interior

Washington, DC 20240
This report should be cited as:

Armbruster, M.J. 1987. Habitat suitability index models: greater sandhill

crane. U.S. Fish Wildl. Servo Biol. Rep. 82(10.140). 26 pp.
PREFACE

This document is part of the Habitat Suitability Index (HSI) model series

[Biological Report 82(10)J, which provides habitat information useful for

impact assessment and habitat management. Several types of habitat information

are provided. The Habitat Use Information section is largely constrained to

those data that can be used to derive quantitative relationships between key

environmental variables and habitat suitability. This information provides

the foundation for the HSI model and may be useful in the development of other

models more appropriate to specific assessment or evaluation needs.

The HSI Model section documents the habitat model and includes information

pertinent to its application. The model synthesizes the habitat use information into a framework appropriate for field application and is scaled to

produce an index value between 0.0 (unsuitable habitat) and 1.0 (optimum

habitat). The HSI Model section includes information about the geographic

range and seasonal application of the model, its current verification status,

and a list of the model variables with recommended measurement techniques for

each variable.

The model is a formalized synthesis of biological and habitat information

published in the scientific literature and may include unpublished information

refl ect i ng the opi ni ons of i dent ifi ed experts. Habi tat i nformat i on about

wil dl ife speci es frequently is represented by scattered data sets co" ected

during different seasons and years and from different sites throughout the

range of a species. The model presents this broad data base in a formal,

logical, and simplified manner. The assumptions necessary for organizing and

synthesizing the species-habitat information into the model are discussed.

The model should be regarded as a hypothesis of species-habitat relationships

and not as a statement of proven cause and effect relationships. The model

may have merit in planning wildlife habitat research studies about a species,

as well as in providing an estimate of the relative suitability of habitat for

that species. User feedback concerning model improvements and other suggestions that may increase the utility and effectiveness of this habitat-based

approach to fish and wildlife planning are encouraged. Please send suggestions

to:

Resource Evaluation and Modeling Section

National Ecology Center

U.S. Fish and Wildlife Service

2627 Redwing Road

Ft. Collins, CO 80526-2899

iii
iv
CONTENTS

PREFACE iii

FIGURES vi

ACKNOWLEDGMENTS vi i

HABITAT USE INFORMATION 1

Genera 1 1

Food 2

Water 3

Cover 3

Reproduct i on 4

Interspersion and Composition........................................ 5

Special Considerations............................................... 6

HABITAT SUITABILITY INDEX (HSI) MODEL ,. 7

Model Applicability.................................................. 7

Model Description.................................................... 10

Appl ication of the Model 19

SOURCES OF OTHER MODELS 22

REFERENCES 23

v
Number

1

2

3

4

5

6

7

FIGURES

Approximate geographic area of applicability for the greater

sandhill crane HSI model in the contiguous United States .....

Relationship between classification of wetlands (Cowardin

et al. 1979) on the evaluation area and their respective

suitability indices .

Relationship between water regimes of wetlands (Cowardin

et al. 1979) located on the evaluation area and suitability

indices .

Relationship between the percent of the evaluation area

in wetland and the suitability index .

Relationship between the size of an evaluation area

and its suitability index ..

Relationships of habitat variables, cover types, and life

requisites to the HSI for greater sandhill crane habitat

Definitions of variables and suggested measurement

techn i ques .

vi

8

13

14

15

17

20

20
ACKNOWLEDGMENTS

I gratefully acknowledge the constructive reviews of Jerry Bartelt, Alan

Bennett, David Best, Jeff DiMatteo, Roderick Drewien, Donald Frickie, Ronald

Hoffman, Richard Hunt, James Kesel, James Lewis, Carroll Littlefield, Janet

Smith, Scott Swengel, and Lawrence Walkinshaw. Several of these individuals

also contributed reprints and/or unpublished information. The assistance of

these individuals contributed greatly to the improvement of this model and is

sincerely appreciated.

Thi s document was ill ustrated by Jenni fer Shoemaker and Susan Strawn.

Word processing was provided by Carolyn Gulzow, Dora Ibarra, Elizabeth Graf,

and Patricia Gillis.

vii
GREATER SANDHILL CRANE (Grus canadensis tabida)

HABITAT USE INFORMATION

General

Six subspecies of sandhill cranes (Grus canadensis) are currently

recognized (Lewis 1977). There are three nonmigratory forms: the Florida (G.

~. pratensis), the rare Cuban (9. ~. nesiotes), and the endangered Mississippi

sandhill crane (9. ~. pulla) (King 1981). The lesser (g. ~. canadensis) and

the Canadi an sandhi 11 cranes (G. c. rowani) are the most abundant of the

mi gratory subspeci es. Thi s model attempts to cha racteri ze the reproductive

habitat requirements of the greater sandhill crane (G. c. tabida), a subspecies

that nests from latitude 40 degrees in the northern-United States to 50 degrees

north in southern Canada (Walkinshaw 1973).

Four distinct populations of greater sandhill cranes have been identified

(Lewis 1977). The Eastern population nests in parts of Michigan, Wisconsin,

Minnesota, Ontario, Manitoba (Lovvorn and Kirkpatrick 1981a), Illinois

(Greenberg 1980), and Indiana (R.H. Hoffman, 6142 Territorial Road, Pleasant

Lake, MI; 1etter dated September 7, 1985) and winters in Florida. The Rocky

Mountain population nests in northwestern Colorado; northeastern Utah, western

Wyomi ng, southern Montana, and southea stern Idaho (Drewi en and Bizeau 1974)

and winters in New Mexi co, southeastern Ari zona, and northern Mexi co. The

Colorado River Valley population nests in northeastern Nevada and probably

southwestern Idaho and winters along the Colorado River in Arizona and southern

California (Drewien et al. 1976). The Central Valley population nests

primarily in Oregon and northeast California, but there is an undetermined

number of cranes nest i ng in southern Bri t ish Col umbi a and Washington (C. D.

Littlefield, Malheur Field Station, Princeton, OR; letter dated February 24,

1986). This population winters in the Central Valley of California

(Littlefield and Thompson 1979).

Greater sandhill cranes occur in North Dakota during fall migration

(Johnson and Stewart 1973) and in southern Texas during the winter (Guthery

and Lewis 1979; Tacha et al. 1986), but have not been associated with any of

the four populations described above. A possible breeding area for these

birds is the Interlake region of southcentral Manitoba (Lewis 1977; Melvin and

Temple 1983). It is likely that the greater sandhill cranes breeding in and

around Agassiz National Wildl ife Refuge (NWR) in northwestern Minnesota and

wintering near the Texas coast are members of this population (J. DiMatteo,

Department of Biological Sciences, St. Cloud State University, St. Cloud, MN;

letter dated February 27, 1986).

1
Greater sandhill cranes were officially listed as rare by the U.S.

Department of the Interior in 1966 (U.S. Fish and Wildlife Service 1966), but

were delisted in 1973 (U.S. Fish and Wildlife Service 1973). The Conservation

Committee of the Wilson Ornithological Society estimated population size and

status in 1975 as: Eastern, approximately 7,000 birds with population increasing; Rocky Mountain, 10,000-15,000 birds and increasing; Colorado River Valley,

1,000 birds with population status unknown; and Central Valley, approximately

3,500 birds and stable (Drewien et al. 1975). Since 1975, portions of the

Central Valley population have been declining because of low annual recruitment

(Littlefield and Thompson 1979; Stern et al. 1987). The size of the Eastern

population was more recently estimated at approximately 15,000 birds (Lovvorn

and Kirkpatrick 1981b); however, >6,000 cranes were surveyed in Wisconsin

alone in 1985 (R.A. Hunt, Wisconsin Department of Natural Resources, Horicon

Area Headquarters, Horicon, WI; unpubl.). Guthery and Lewis (1979) estimated

that approximately 2,000 greater sandhill cranes wintered in south Texas in

the early 1970's (Interlake population?), but the current size and status of

this population is unknown.

Food

Sandhill cranes feed on a variety of plant and animal foods (Walkinshaw

1949) and can be categorized as opportunistic omnivores (Mullins and Bizeau

1978). Young cranes (colts) are fed by the pair for the first few days of

life (Walkinshaw 1973) and then feed almost exclusively on animal food during

the preflight period (Lewis 1977). Cranes nesting at Grays Lake, Idaho,

confined their foraging activities to the nesting territory in good food years

until the young were old enough to fly (Drewien 1973). In years of limited

food, crane families leave their territories to search for food (R.C. Drewien,

Grays Lake National Wildlife Refuge, Wayan, ID; letter dated September 27,

1985). Marsh-nesting cranes in Michigan also used their territories for

feeding (Walkinshaw 1973). Cranes in Colorado, however, moved away from

streambank nests after their eggs hatched and foraged in surrounding uplands

supporting sagebrush (Artemisia spp.) and aspen (Populus tremuloides) stands

(Bieniasz 1979). Greater sandhill cranes nesting in the Upper Peninsula of

Michigan foraged in forest openings away from their bog nest sites (Taylor

1976).

Food items taken by marsh-nesting cranes include roots, browsed vegetation, snails (Helisoma spp.), crayfish (Cambarus spp.), small mammals, birds,

frogs (Hyla crucifer, Rana pipiens), snakes, toads (Bufo spp.), and various

insects (Walkinshaw 1973). Cranes will apparently attempt to take any potential food item of the proper size, including waterfowl eggs (Bennett 1978;

Hoffman 1980) and ducklings (Littlefield 1976b). Large food items such as

garter snakes (Thamnophis sirtalis) are torn apart by the adults before being

fed to the chick (Bennett 1978).

Cranes nesting on small wetlands in southern Wisconsin made extensive use

of uplands as feeding sites after their chicks hatched (Bennett 1978). Adults

remained close to the nest for the first 2 days after hatching but then moved

colts to upland feeding sites at 3-4 days of age. Cattle pastures that were

heavi ly grazed seemed to be preferred by feedi ng cranes. Sites with short

vegetation permitted easy movement for colts searching for the abundant soil

2
invertebrates associated with moist depressions and cattle manure. The use of

upland sites continued until the colts were approximately 5 weeks of age, at

which time family groups shifted feeding activities back to wetlands (Bennett

1978).

Cranes often feed in grain fields in the spring before nest sites thaw

and again in 1ate summer after the young reach fl i ght stage. Heavi ly used

grains include barley (Hordeum vulgare) in Idaho (Drewien 1973), wheat

(Triticum aestivum) in Colorado (Bieniasz 1979), and corn (Zea mays), wheat,

and other crops in Michigan (Hoffman 1976; Taylor 1976) and Wisconsin (Bennett

1978). Hamerstrom (1938) felt that grain fields of buckwheat (Fagopyrum

escul entum), corn, and oats (Avena sativa) were an important food source in

areas of small marshes and interspersed agriculture.

Water

Cranes drink water and seem to prefer a pH range from 4.5 to 7.6 for

their aquatic activities in the upper midwest (Walkinshaw 1973); however,

western populations may tolerate more alkaline conditions (Drewien, unpubl.).

Food, cover, and nesting requi rements for sandhi 11 cranes are i nt imate ly

associated with water in the form of some type of wetland. Water requirements

are di ffi cul t to separate i ndi vi dually and are di scussed under the habi tat

component supplied.

Cover

A roost site is synonymous wi th nocturnal securi ty cover for cranes.

Many authors have alluded to the importance of roost sites within the nesting

terri tory, but 1itt1equanti tati ve i nformat i on has been presented for the

greater sandhill crane. Walkinshaw (1973) characterized roosting sites in

Mi chi gan as standi ng water 10 to 30 cm deep surrounded by deeper water or

large expanses of marsh. The mean distance from roost sites to a nest site

was 140 m. Cranes nesting in the Hiawatha National Forest in Michigan roosted

within 3 km of the nest site (Taylor 1976). Hamerstrom (1938) and Crete and

Grewe (1981) felt that ice formation and the resulting absence of open water

for night roosting was the causal factor initiating fall migration from

Wisconsin staging areas.

Bennett (1978) characterized 10 roost sites in southeastern Wisconsin.

The actual roost sites were small (1.4 ha), but were all centered in large

wetlands >300 ha in size. Cranes roosted in the open-water zone (5 to 15 cm

deep) beyond the edge of emergent vegetation. Vegetation surrounding the

roost site varied from aquatic emergents, such as cattails and American lotus

(Nelumbo lutea), to oak (Quercus spp.) forest.

The characteristics of roost sites used during migration are better

documented than are breedi ng season roosts. Greater sandhi 11 cranes of the

Eastern population selected roosts in northwestern Indiana with water <20 cm

deep and free from human disturbance (Lovvorn and Kirkpatrick 1981a). Stable,

uniformly shallow water conditions are important, and bare or sparsely

vegetated mud flats surrounding the site seem to be preferred. Cranes avoid

disturbance by maximizing either distance or visual isolation from human

3
activity. For example; the average mt mmum distance from human activities in

Indi ana was 140 m for roosts surrounded by woody vegetation and 380 m for

roosts visible from a road (Lovvorn and Kirkpatrick 1981a).

Reproduction

Most authors identify the primary components of greater sandhill crane

reproductive habitat as a nest site, roosting area, feeding area, and isolation. These components can be supplied by large marsh complexes (Littlefield

and Ryder 1968; Drewien 1973); smaller, scattered marshes (Hamerstrom 1938;

Walkinshaw 1973; Hoffman 1983); bogs in northern boreal forests (Taylor 1976);

intermittent streams in sagebrush parklands (Bieniasz 1979); and mountain

meadows, beaver (Castor canadensis) ponds, and subirrigated wet meadows along

riparian zones (Drewien and Bizeau 1974). The specific identity of the cover

type does not appear to be as important as is the juxtaposition of water

(supplying a nest and roosting site) and a food source, in an isolated

situation.

Cranes mate for life (Walkinshaw 1949) and return to the same territory

each year (Drewien 1973). Both members of the pair participate in defense of

the territory, nest building, and incubation (Littlefield and Ryder 1968;

'Drewien 1973; Walkinshaw 1973). The male is the most active in territory

defense. Littlefield and Ryder (1968) reported that, under crowded conditions

(six nests in close proximity), males became preoccupied with territorial

defense and failed to relieve their incubating mates. Five of six nests were

lost to predators when the female finally left the nest to feed.

Nests are usually constructed from residual vegetation from the previous

growing season (Littlefield and Ryder 1968; Drewien 1973; Walkinshaw 1973).

Of 174 nests found in southern Mi chi gan, 38~~ were buil tin cattails (Typha

latifolia, I. angustifolia), 35~~ in sedges (Carex spp.), 17% in bulrushes

(Scirpus validus), 6% in water willow (Decodon verticillatus), and 4% in

mi sce 11 aneous plants (Walkinshaw 1973). Fifty-four percent of 113 nests were

found in burreed (Sparganium eurycarpum) on Malheur NWR, Oregon, while 24.8%

were located in hardstem bulrush (S. acutus), 9.7% in cattail (T. latifolia),

and 11.5% in miscellaneous grasses, forbs, and willows -(Salix spp.)

(Littlefield and Ryder 1968). ------

Marsh vegetation occurred in a heterogeneous mixture at Grays Lake NWR,

Idaho, and cranes appeared to use whatever was encountered for nesting (Drewien

1973). Dominant vegetation at 26.5% of nest sites was rush (Juncus balticus),

23.7% sedges, 12.2% hard stem bulrush, and 19.7% in three other genera accounting for >5% canopy coverage. Limited use of muskrat (Ondatra zibethica)

lodges (Drewien 1973; Walkinshaw 1973), dikes and islands in deep marshes

(Drewien 1973), and beaver dams (Bieniasz 1979), as nest sites, has been

reported. Nests located in pastures near water at Grays Lake were constructed

of cattle manure (Drewien 1973). Cranes nesting along small streams in

Colorado used grasses and willow twigs remaining from beaver cuttings for nest

materials (Bieniasz 1979).

4
Water depth, or proximity to water, may be more critical to nest placement

than is vegetation type. Nests are usually located in, or next to, shallow

water, and may require from 1 day to over a week to construct (Littlefield and

Ryder 1968; Drewien 1973). Although wetland Types 1-8 (Shaw and Fredine 1956)

were available in a Waterloo Township, Michigan, study area, only Types 3

(shallow marsh) and 4 (deep marsh) were used for nesting (Hoffman 1983). (A

comparison between this wetland classification and a more recent system devised

by Cowardin et al. 1979 is presented later in the model.) Sixty-five percent

of these wetlands contained open water or were associated with a lake.

Seventy-five percent of 377 nests located at Grays Lake NWR were situated in ~25 cm of water or built on dry ground within 4.6 m of water (Drewien 1973).

Nests were usually built around the periphery of the hardstem-bulrush-dominated

marsh, with many cranes avoiding the deeper water dominated by bulrush and

cattail. Grays Lake is actually a 8,900 ha Type 3 marsh. with some areas that

could be classified as Type 4. At lower water levels. cranes do use the

bulrush and cattail-dominated areas. indicating a selection for water depth

and not plant cover type (Drewien, unpubl.). Crane nests at Malheur NWR were

located in, or very near. standing water averaging 16.8 cm in depth

(Littlefield and Ryder 1968). The average water depth around 144 nests in

southern Michigan was 25.3 cm (Wal kinshaw 1973). Nests found in northern

Colorado sagebrush parks were always situated along willow-lined streams

within 1 m of slow-moving water 15 to 16 cm deep (Bieniasz 1979).

Isolation from human activity appears to be an important criterion for

se 1ect i on and use of nest i ng territori es by cranes. Severa 1 authors have

commented on the propensity of cranes to desert their nests due to human

disturbances (Littlefield and Ryder 1968; Drewien 1973; Walkinshaw 1973;

Bieniasz 1979). Drewien (1973) noted the absence of nesting in a section of

Grays Lake marsh located close to roads and cultivated fields. The few nests

located <400 m from roads were screened by tall vegetation. Marshes (n =26)

used for nesting in Mi chi gan were an average 320 m from cul t i vated fi e1ds ,

431 m from roads. and 476 m from residences (Hoffman 1983). Cranes nesting in

the Upper Peninsula of Michigan occupied remote bogs (wetland Type 8 of Sha~

and Fredine 1956) located in extensive forest stands (Taylor 1976). Vegetation

associated with these wetlands included sphagnum moss (Sphagnum spp.). leatherleaf (Chamaedaphne calyculata). cottonsedge (Eriophorum spp.). black spruce

(Picea mariana), and jack pine (Pinus banksiana). Type 8 wetlands composed

32% of 113 wetlands surveyed on the Manistee National Forest in Michigan. but

accounted for 74% of 31 wetlands judged as good or excellent crane habitat

(L.H. Walkinshaw. 915 North Onondaga Road, Holt. MI; unpubl.). Cranes nesting

in northern Colorado utilized small willow-lined drainages separated by

sagebrush-covered ridges (Bieniasz 1979). Poor vehicular access to this high

mountain park usually afforded isolation to nesting cranes until midincubation.

Interspersion and Composition

Drewien (1973) and Walkinshaw (1973) both believed that most greater

sandhill cranes maintain a classic Type A territory (Hinde 1956) that supplies

all courtship, mating, nesting. and food requirements; however. both of these

researchers worked in very productive marshes. For example. Grays Lake may

well offer close to ideal conditions for nesting cranes by supplying a

5
diversity of cover types, from upland meadow to bulrush-cattail marsh, in

close proximity around the periphery of a 8,900 ha marsh. Cranes can therefore

maintain a breeding space in a fairly small physical area. Indeed, crane

breeding densities at Grays Lake are the highest reported anywhere (Drewien

1973).

Food availability influences local movements and the duration of crane

occupancy on the defended territory (Drewien 1973). Five territories at Grays

Lake averaged 17 ha, and most families remained on site until young fledged.

Drewien (1973) felt that 5 to 8 ha would be the minimum area required to

support a nesting pair at Grays Lake. Eight territories at Malheur NWR averaged 25 ha (L itt1efi e 1d and Ryder 1968), and territory size for 76 Mi chi gan

(Lower Peninsula) nests averaged 53 ha (Walkinshaw 1973). In the latter

study, however, cranes apparently fed in fields located some distance from the

defended nest site. Colorado cranes moved up to 0.8 km to sagebrush and aspen

feeding areas (Bieniasz 1979), and bog nesting cranes in the Upper Peninsula

of Michigan foraged in forest openings within a 3-km radius of the nest site

(Taylor 1976). Drewien (unpubl.) has observed crane families searching for

food >5 km from nesting territories during years of food shortages.

Hoffman (1983) calculated and compared the density of pairs in terms of

'total area used in several studies (Table 1). Density is dependent on area

coverage and other, nonhabitat-related, variables that may not be comparable

between studies, but the data presented in Table 1 should give some indication

of relative trends among different local populations of cranes. Densities on

breeding marshes in Marquette and Green Lake counties of Wisconsin (a subset

of Bennett's 1978 study area) now exceed 2.0 pa t r-s/km" (S. Swengel,

International Crane Foundation, Baraboo, WI; letter dated September 11, 1985).

The above discussion indicates a behavioral flexibility of cranes to

exploit food resources well removed from the defended area. In fact, the only

critical habitat component common to all studies is a secure (isolated) nest

site that is almost always associated with water. Size of wetland seems

irrelevant as long as security is provided. Hamerstrom (1938:180) found

cranes nesting in shallow water marshes of at least 16 ha in size, but

additional security was provided to this II sma11 nuc l eus" by a larger zone of

aspen and grass marsh of at least 400 ha. Cranes nested on bogs as small as

0.2 ha in northern Michigan but never near human activities (Taylor 1976).

Cranes will nest on beaver ponds as small as 0.04 to 0.08 ha, and Drewien

(unpubl.) found several nests around wet seeps or springs in aspen-mountain

shrub cover types. Cranes nesting on dry land at Grays Lake may be indicative

of the 1i mited exposure to nest predation experi enced by thi s popul ation

(Drewien 1973).

Special Considerations

Adult cranes are long lived, but mortality can be high for eggs and

young. Ravens (Corvus corax), raccoons (Procyon lotor), and coyotes (Canis

latrans) destroyed eggs and killed young at Malheur NWR (Littlefield 1976b;

Littlefield and Thompson 1987). Coyotes, common ravens, and California gulls

(Larus californicus) were identified egg predators at Sycan Marsh, Oregon

6
Table 1. Comparison of greater sandhill crane densities from studies

reporting use of both wetlands and uplands (from Hoffman 1983).

Pairs/km2

Investigator Location (wetland and upland)

Drewien (1973) Idaho 2.00

Littlefield (1976a) Oregon 0.30

Hoffman (1983) Michigan (1982) 0.30

(1970) 0.20

Halbeisen (1980) Michigan 0.10

Bennett (1978) Wisconsin ( 1977) 0.03

(1976 ) 0.02

(Stern et al. 1987). Raccoons were also important nest predators in Michigan

(Walkinshaw 1973). Striped skunks (Mephitis mephitis), crows (Corvus

brachyrhynchos), and ravens were the pri nci pa1 egg predators at Grays Lake,

and a golden eagle (Aguila chrysaetos) killed and devoured an adult male crane

incubating eggs (Drewien 1973). Bieniasz (1978) observed two adult cranes

drive a swift fox (Vulpes velox) away from their colt, but Drieslein and

Bennett (1979) believed red foxes (y. vulpes) can be an important predator on

chicks up to 1 week of age. Littlefield and Ryder (1968) and Drewien (1973)

reported adult mortalities resulting from collisions with powerlines anq

barbed-wire fences.

Cranes can cause serious crop damage. Wheat, both the kernels and new

growth 5 to 10 cm ta 11, seems to be preferred, with corn a close second

(Hoffman 1976). Cranes in the Upper Peninsula of Michigan caused some crop

damage at fall staging areas (Taylor 1976) and to recently planted wheat

(fall) and corn (spring) in southern Michigan (Hoffman 1976) and Wisconsin

(Hunt and Gluesing 1976). Barley has been heavily damaged by cranes at the

Grays Lake staging area (Drewien 1973). Some damage to wheat during staging

periods has been reported from northern Colorado (Bieniasz 1979).

HABITAT SUITABILITY INDEX (HSI) MODEL

Model Applicability

Geographic area. This model was developed for application within the

breeding range of the five extant populations of greater sandhill cranes in

the United States (Figure 1). Figure 1 should not be interpreted as an attempt

7
Figure 1. Approximate geographic area of applicability for the greater

sandhill crane HSI model in the contiguous United States. Shading does

not imply continuous current distribution, or that adjacent areas are

unsuitable. For example, some nesting occurs in Washington, but the

locations and magnitude are unknown (Littlefield, unpubl.).

to define specific areas currently occupied by breeding greater sandhill

cranes. Rather, Figure 1 identifies the general locations presently used by

the five crane populations described in this report, as well as intervening

and surrounding areas that may be appropriate for model appl ication. The

distribution of greater sandhill cranes in southern Canada is not well known

(Tebbel and Ankney 1979).

Season. The model was developed for application during the breeding

season, from first arrival on site in late March-early April, until approximately mid-September, when young can fly.

Cover types. Thi s model focuses on wetlands and can be app 1i ed to

Forested Wetland (FW), Scrub-shrub Wetland (SW), Herbaceous Wetland (HW),

Ri veri ne (R), and Lacustri ne (L) types (termi no logy follows U. S. Fi sh and

Wildlife Service 1981). The model also requires the application of the wetland

class and water regime descriptors of Cowardin et al. (1979). Surrounding

uplands considered in this model include Cropland (C), Grassland (G), Pasturel

Hayland (P/H), Deciduous Forest (OF), and Evergreen Forest (EF). All other

types can be classified as nonforested uplands.

8
Minimum habitat area. Minimum habitat area is defined as the mi mmum

amount of contiguous habitat that is required before a species will occupy an

area. The smallest area used for nesting by greater sandhill cranes was a

0.2 ha bog in northern Michigan (Taylor 1976). It is unclear, however, whether

or not the pair obtained all their food requirements from this area, or if

they nested successfully. Most studies stress the importance of isolation of

the nest site rather than the specific size or type of wetland used. For

these .reasons, no particular minimum size limit for a wetland is defined here.

It is the responsibility of the user to determine if a wetland is large enough

to support crane nesting.

Verification level. This model provides information useful for baseline

assessments and habitat management. The potential of an area to support

nesting greater sandhill cranes is described. The model is intended for

planning applications over large geographic areas using good quality aerial

photography. The model is a set of hypotheses describing assumed crane-habitat

relationships and does not reflect proven cause and effect. The model should

rank the qual ity of potential nesting areas as would an expert thoroughly

familiar with the reproductive requirements of greater sandhill cranes.

Earlier drafts of this model were reviewed by:

Jerry Ba rte It, Department of Natura 1 Resources, Horicon Area Headquarters,

Horicon, Wisconsin.

Alan Bennett, Okefenokee National Wildlife Refuge, Fo'lkston, Georgia.

David Best, U.S. Fish and Wildlife Service, East Lansing, Michigan.

Jeff DiMatteo, Department of Biological Sciences, St. Cloud State University,

St. Cloud, Minnesota.

Roderick Drewien, Idaho Cooperative Wildlife Research Unit, University of

Idaho, Moscow, Idaho.

Donald Frickie, Seney National Wildlife Refuge, Seney, Michigan.

Ronald Hoffman, 6142 Territorial Road, Pleasant Lake, Michigan.

Richard Hunt, Department of Natural Resources, Horicon Area Headquarters,

Horicon, Wisconsin.

James Kesel, Seney National Wildlife Refuge, Seney, Michigan.

James Lewis, U.S. Fish and Wildlife Service, Albuquerque, New Mexico.

Carroll Littlefield, Malheur National Wildlife Refuge, Burns, Oregon.

Janet Smith, U.S. Fish and Wildlife Service, Green Bay, Wisconsin.

9
Scott Swengel, International Crane Foundation, Baraboo, Wisconsin.

Lawrence Walkinshaw, 915 North Onondaga Road, Holt, Michigan.

Modifications suggested by these individuals have been incorporated into the

model where possible. Use of the reviewers· names, however, does not necessarily imply that they concur with each section of the model, or the model in its

entirety.

Model Description

Overview. The model is designed to evaluate a site's potential to support

nesting greater sandhill cranes. The model identifies a range of suitability

in terms of the assumed requirements supplied for each variable used to characterize habitat potential. Suitability is defined in terms of the assumed

relationships between optimum conditions and the opposite extreme of no

resources available. Conditions identified as optimum are often a compromise

between biological and management considerations. For example, present

critical habitat components appear to be met by wetland/upland complexes

.isolated from human disturbances during the March-June nesting period. From a

practical standpoint, nest sites, roosting areas, and food can be most

efficiently provided by large areas intensively managed for nesting sandhill

cranes.

Optimum habitat conditions are assumed to exist when all requirements

occur in close proximi ty over 1arge contiguous areas, such as the marshes

and/or wet meadows, and adjacent uplands at Grays Lake and Malheur NWR ' s.

Wilson (1983) developed a greater sandhill crane pattern recognition model for

southeastern Idaho and assumed that cranes could reach a nesti ng density of

6.2 pai rs./km! under optimum conditions. This is similar to a density of 6

pairs/km2 estimated from Drewien's (1973) data from Grays Lake. Other areas

support nesting cranes but in lower densities. Although no data are presented

for crane nesting densities in Colorado (Bieniasz 1979) or northern Michigan

(Taylor 1976), descriptive information indicates densities of <0.1 pairs/km2 •

These areas will receive some value as nesting habitat when evaluated with

this model. However, it is assumed that other types of smaller wetlands and

associated uplands cannot physically provide the optimum habitat conditions

that will support crane-nest densities occurring on large marsh/upland

complexes used as the standard of comparison in this model. This model assumes

that the habitat potential of a site can be characterized by the identity of

the wetland class(es), water regime(s), percent of the area in wetlands, and

the size of the site.

Food/reproduction component. Habitat-use patterns differ between the

various segments of the five extant populations (including Interlake population) of greater sandhill cranes nesting in the United States and parts of

southern Canada. Two factors, however, are shared by all segments: association

of the nest site with some type of wetland and isolation from human activities.

Because large wetland complexes that can supply secure nest and roost sites

10
also have the potential of supplying all food requirements, food and reproduction needs are considered together as the critical habitat component of this

model. Water, cover, and spatial requirements are assumed to be synonymous

with, or never more limiting than, the minimum requirements for food and

reproduction as defined in this model.

The most commonly cited criterion used to describe crane habitat is the

presence of some type of wetland. Wetland definitions abound, but for the

purposes of this model:

WETLANDS are lands transitional between terrestrial and aquatic

systems where the water table is usually at or near the surface or

the land is covered by shallow water .... wetlands must have one or

more of the following three attributes: (1) at least periodically,

the land supports predominantly hydrophytes; (2) the substrate is

predominantly undrained hydric soil; and (3) the substrate is nonsoil

and is saturated with water or covered by shallow water at some time

during the growing season of each year (Cowardin et al . 1979:3).

Much of the crane literature that identifies wetland use is founded on

the classification system of Shaw and Fredine (1956). In contrast, most of

the current wetland inventory work underway by the U. S. Fi sh and Wildl ife

Service's National Wetland Inventory Project utilizes the classification

system of Cowardin et al. (1979). This model will follow the latter system.

Persons with data in the format of Shaw and Fredine (1956) should refer to

Table 2 for comparisons with the Cowardin et al. (1979) system. The following

variables are used to determine the quality of an evaluation site in terms of

the wetland(s) it supports and the assumed value to greater sandhill cranes.

Optimum conditions for food and reproduction are assumed to exist in

emergent wetlands (SIV1, Figure 2) supporting erect, rooted, herbaceous hydrophytes such as cattails, bulrushes, sedges, and other plants commonly used for

nest building. Emergent wetlands (a class level descriptor in Cowardin et al.

1979) are also assumed to provide a more diverse and abundant potential food

supply than exists in other wetland classes. Cranes do use scrub-shrub

(Walkinshaw 1965; Littlefield and Ryder 1968; Bennett 1978; Bieniasz 1979) and

forested wetlands (Taylor 1976), but their relative value as nesting cover is

unclear. Bennett (1978) found several thousand hectares of shrub swamp in

southeastern Wisconsin that received no crane use, but tamarack (Larix

1ari ci na) swamps conta i ni ng openi ngs domi nated by catta il s and sedges were

consistently used by nesting cranes (A. Bennett, Okefenokee National Wildlife

Refuge, Folkston, GA; letter dated January 23, 1986). In fact, townships

supporti ng the hi ghest ratio of shrub swamps had the small est crane popul ations. It is unclear, however, whether cranes were responding to the presence

of shrubs, or to lowered water levels resulting from attempts at wetland

dra i nage. Because of these uncerta i nti es, scrub-shrub, forested, and mosslichen wetlands are assigned rather low values (relative to emergent wetlands).

I have assumed that wetlands classified as unconsolidated bottom or aquatic

bed are characterized by water levels too deep to support emergent vegetation

or crane use.

11
Table 2. Comparison of the wetland types of Shaw and Fredine (19S6) with the wetland classes and water

regime modifiers of Cowardin et al. (1979).

Shaw and Fredine (1956) Cowardin et al. (1979)

a We t Ia nd type We t Iand c Iass Water regime Water regime definitions

1. Seasonally flooded

basins or flats

Emergent wetland

Forested wet land

Temporari Iy flooded Surface water present for brief periods during growing season, but water table usually lies

wei I below soil surface for most of season

2. Inland fresh meadows Erne rgent wet Iand

Intermittently

flooded

Saturated

Substrate usually exposed, but surface water

is present for variable periods without

detectable seasonal periodicity

Substrate saturated to surface for extended

periods during growing season, but surface

water seldom present

.....

N

3. Inland shallow fresh

rna rshe s

Emergent wetland Semipermanently

flooded

Seasonally flooded

Surface water persists throughout growing

season in most years

Surface water present for extended periods, especially early in growing season, but

absent by end of season in most years

II. In Iand deep fresh

rna rshes

[me rgent wet Iand Permanently flooded Water covers land surface throughout year in

a I I yea rs

Aqua t ic bed Intermittently

exposed

Surface water present throughout year except in years of extreme drought

Semipermanently

flooded

(As defined above)

5. Inland open fresh

water

Aqua tic bed Permanently flooded (As defined above)

AI I water regimes defined here except permanently flooded

(As defined above)

Sa tu ra ted (AS defined above)

Intermittently

exposed

All water regimes defined here except permanently flooded

Forested wetland

Unconso I ida ted

bottom

Scrub-shrub wetland

Scrub-shrub

6. Shrub swamps

7. Wooded swamps

8. Bogs

Forested wetland

Moss-lichen wetland

aCrane use has been reported only from wetland types 1-8; therefore, types 9-20 are not addressed.

- -
1.0 .--.

-:>

.......

V') 0.8

x

Q)

"0 0.6 c

.......

>,

-+J 0.4

..0 0.2 ttl

-+J

:::::l

V') 0.0 ..

Wetland class

1. Emergent wetland

2. Scrub-shrub wetland

3. Forested or mosslichen wetland

4. Unconsolidated bottom

or aquatic bed

1 2 3 4

Figure 2. Relationship between classification of wetlands (Cowardin

et al. 1979) on the evaluation area and their respective suitability

indices.

The presence of water, at 1east through hatchi ng, is assumed to be a

critical factor in determining the suitability of an area for greater sandhill

cranes. Cranes utilize relatively shallow water for their aquatic activities.

Recorded water depths for both roosting and nest site location usually fall

between 10 and 30 cm (Littlefield and Ryder 1968; Drewien 1973; Wa"lkinshaw

1973; Lovvorn and Kirkpatrick 1981a), although the use of mud flats for

roosting (Lovvorn and Kirkpatrick 1981a) and nests placed on bare ground in

close proximity to water (Drewien 1973; Bieniasz 1979) are not uncommon in

some situations. Deeper water interspersed with water 10 to 30 cm deep may

provide security from terrestrial predators (Walkinshaw 1973).

Water depths in wetlands used by greater sandhill cranes often fluctuate

during the breeding season in response to snow melt, irrigation drawdown,

natural evaporation, and other factors. Because of these fluctuations, an

estimate of relative water permanence is assumed to be a better indicator of

habi tat sui tabi 1ity than woul d be some estimate of mean depth. The water

regime descri ptors of Cowardi n et a 1. (1979) are used to rank the permanence

and timing of water availability for crane feeding, roosting, and nesting

activities (SIV2, Figure 3). The assigned ranks reflect the assumption that

13
1.0 N

:>

V) 0.8

x

Q)

-0 0.6 c

>,

+-' 0.4 .~

.0

ro 0.2

+-'

:::J

V) 0.0

· I--

· ,... - · I--

-

Water regime

1. Permanently flooded

2. Intermittently exposed

3. Semi permanently flooded

4. Seasonally flooded

5. Saturated

6. Temporarily flooded

7. Intermittently flooded

1234567

Figure 3. Relationship between water regimes of wetlands (Cowardin

et al. 1979) located on the evaluation area and suitability indices.

semipermanently and seasonally flooded wetlands will provide reliable water

sources but are still shallow enough to support emergent hydrophytes and crane

use. Using the same logic, intermittently flooded wetlands do not exhibit a

reliable water source and are of limited value, whereas wetlands permanently

flooded are probably too deep for crane use and emergent herbaceous hydrophyte

growth. Intermi ttently exposed, saturated, and temporari ly fl ooded wet1ands

are assigned ranks assumed to reflect water permanence and resultant suitability as crane habitat. Artificially flooded wetlands, or those sites where the

amount and duration of flooding is controlled by man, are not addressed in

Figure 3. Model users dealing with artificially flooded wetlands are encouraged to assign ranks that best approximate the definitions presented in Table 2.

The minimum amount or percent of the area required in wetland is unknown,

but for some areas in southern Idaho, Orewien believes that a direct relationship exists between the presence and the amount of wet meadow and the

occurrence and extent of crane nesting activity (R.C. Orewien, Idaho

Cooperative Wildlife Research Unit, Moscow, 10; pers. comm. in Wilson 1983).

The maximum amount or percent of wetland required in an area is also unknown.

14
Wilson (1983) indicated that the presence of some (minimum of 60.8 ha/km

segment) upland meadow adjacent to wet meadows along willow-lined streams

increased the probability of high densities of nesting cranes.

Uplands are also important crane-use areas around large marshes such as

Agassiz (J. DiMatteo, Agassiz National Wildlife Refuge, Middle River, MN;

letter dated September 12, 1985), Grays Lake (Drewien, unpubl.), Malheur (C.D.

Littlefield, Malheur National Wildlife Refuge, Burns, OR; letter dated

September 16, 1985), and Horicon NWR's (Swengel, unpubl.). Croplands adjacent

to wetlands are important food sources, and are more valuable to cranes than

forested wetlands of comparable size (DiMatteo, unpubl.; J. Bartelt, Wisconsin

Department of Natural Resources, Horicon Area Headquarters, Horicon, WI;

letter dated September 17, 1985).

I have assumed that a mixture of cover types that includes 40% to 60% of

the area in wetlands has the hi ghest potential suitabil i ty for supplyi ng the

food/reproduction needs of nesting sandhill cranes (SIV3, Figure 4). Although

some threshold response may occur as the percentage of wetlands in an area

increases (Swengel, unpubl.). I have elected to represent the relationship

between 0 to 40% wetland as linear. Areas supporting >60% wetlands are assumed

to decrease in value because of the reduced area of upland available, but I

....- 1.0 M

>.....

(/) 0.8

x

OJ

"'C

t: 0.6 .....

>,

+.> 0.4

..Cl

tU 0.2 +.>

(/) 0.0

0 25 50 75 100

Percent of area in wetland

Figure 4. Relationship between the percent of the evaluation area

in wetland and the suitability index.

15
have arbitrarily limited the reduction in value to a maximum of 0.25 (SIV3 =

0.75 at 100% wetland). It is further assumed that all uplands can be classified as agricultural (cropland, grassland, or hay/pasture), forested (deciduous

and/or evergreen), or nonforested (all other upland types) and assigned

suitability indices equal to emergent, forested, or scrub-shrub wetlands

(Figure 2), respectively.

An area free from human di sturbance is the second most commonly cited

criterion used to describe crane habitat. Human activities can take a variety

of forms and can occur at any time, but cranes are most intolerant of disturbance during the nest initiation-incubation period (Drewien, unpubl.;

Littlefield, unpubl.). For example, fishermen can cause cranes to desert

their nests (Bieniasz 1979; Drewien, unpubl.), and the presence of motorized

boats lowers the potential suitabil ity of wetlands as crane habitat (Swengel,

unpubl.). Road construction can be highly disruptive to nesting cranes

(Littlefield, unpubl.).

Thi s model does not attempt to address all potential di sturbances to

nesting cranes. Instead, I have assumed that the potential for human disturbance to nesting cranes can be represented by existing or proposed roadways.

Historically, cranes selected large marshes or isolated bogs for nest sites

and were intolerant of any human disturbance (Walkinshaw, unpub1.). Now,

however, many local populations are expanding and utilizing wetlands in close

proximity to human developments such as roadways. This is especially true for

the Eastern population where cranes now nest within 100 m of roadways in parts

of Minnesota (DiMatteo, unpubl.), Wisconsin (Bartelt, unpubl.; Hunt, unpubl.),

and Michigan (Hoffman, unpubl.). Crane response to roadways appears to depend

on the intensity and timing of vehicular and foot traffic (DiMatteo, unpubl.;

Drewien, unpub1.), the pair's prior experience with man (Hoffman, unpub1.;

Walkinshaw, unpubl.), the presence or absence of concealing vegetation

(Drewien, unpub1.), and probably numerous other considerations beyond the

scope of this model.

I have assumed that the potential for human disturbance to nesting cranes

can be represented in this model with a 100 m band on either side of existing

or proposed roadways. The area wi thi n thi s zone of i nfl uence should be

considered as unusable habitat during the period encompassing nest initiation

through hatching. This period will vary with location but usually occurs in

the months of April, May, and June. Users of this model are encouraged to

modify the width of the zone of influence around roadways if they do not feel

that 100 m adequately reflects local crane population response to human

activity.

Inherent in the concept of a disturbance-free area is size. The smallest

reported wetland used for nesting by greater sandhill cranes is 0.2 ha in the

Hiawatha National Forest (Taylor 1976). An area of this size, however,

probably could not supply all the food/reproduction needs of the pair and

their colts. The minimum area assumed suitable for supplying food/

reproduction requirements in this model is 16 ha (Drewien 1973; Wilson 1983)

(Figure 5). Note that this assumption is not restricted to wetlands but

includes all cover types within the evaluation area. The size of an area

required to equate to optimum habitat conditions is unknown. For the purposes

16
1.0 0:;:1"

:::-

......

Vl 0.8

x

(lJ

"'0

t: 0.6 ......

>,

-+oJ 0.4

.0

10 0.2 -+oJ

Vl 0.0

0 50 100 150 200

Size of disturbance-free site (ha)

Figure 5. Relationship between the size of an evaluation area and

its suitability index.

of this model, a contiguous area of 200 ha or more was arbitrarily selected as

the minimum size capable of supplying optimum conditions for the food/

reproduct ion requi rements of nesting greater sandhi 11 cranes (Fi gure 5). Two

hundred hectares is the approximate area remaining after a 100 m zone of

influence is removed from around most standard (259 ha) sections.

HSI determination. The mathematical relationships between model variables

were selected to mimic the assumed range of conditions from marginal suitability to optimum habitat. The suitability indices of the variables evaluating wetland class (SIVl) and water regime (SIV2) are assumed to be

compensatory, with a high value for one variable compensating for a low value

in the other. The two remaining variables serve to modify this compensatory

relationship. Applications of this model that produce a 0.0 value for any of

the four variables should be interpreted as indicating that the evaluation

site is unsuitable for breeding greater sandhill cranes.

17
Determination of an HSI requires the del ineation on a cover map of the

area to be evaluated for crane use. The model assumes that a 100 m band along

both sides of active roadways is unusable to greater sandhill cranes. An

active road is defined as any mappable feature capable of supporting

terrestrial vehicular traffic from late March through June. This unusable

area should be identified and removed from consideration as crane habitat

before attempting to apply the model.

The eva 1uat ion site shoul d be stratifi ed into cover types defi ned by

wetland class (Figure 2) and water regime (Figure 3), or if upland, as cropland, grassland, hay/pasture, or as forested or nonforested. The area of each

cover type shoul d be determi ned and used to compute a wetland qual i ty index

(WQI) with equation 1:

WOI

n 1/2

L

i=l (SIVl i x SIV2 i) x WA i = ...:..........:=---------.:...,T=W-:-:A-----.:.------.:..

(1)

where n = the number of wetland cover types in the evaluation area

SIVI.

1

SIV2.

1

= the suitability index (SIV1) for wetland class of wetland

cover type i

= the suitability index (SIV2) for the water regime of wetland

cover type i

= the area in wetland cover type

TWA = the total area of all wetlands in the evaluation area

The WOI should then be adjusted to reflect the value of existing wetlands for

the total evaluation area (TWOI) using equation 2:

TWOI = WOI x SIV3 ( 2)

Assessment areas that are composed entirely of wetlands and are ~200 ha have

an HSI equal to TWOI. If uplands occur on site, however, or the usable area

is <200 ha, then additional steps are required to determine HSI.

18
Uplands are assumed to contribute to the overall food/reproduction

component of crane habitat suitability. The upland value (UV) for assessment

sites containing at least some upland area can be determined using equation 3:

UV =

n

E

i=l (UA i x Vi)

TUA (3)

where n = the number of upland cover types in the evaluation area

UA i = the area in upland cover type i

the index value for upland cover type

(cropland, grassland, or hay/pasture) = non forested = 0.4

where agricultural

1.0; forested = 0.1; or

TUA = the total area of all uplands in the evaluation area

The suitability of the food/reproduction component (SIFR) for the assessment

site is determined by combining the values for both wetlands and uplands using

equation 4:

SIFR = TWQI + UV

2 (4 )

Areas ~200 ha have an HSI equal to SIFR. For areas <200 ha, however, the

value should be reduced using equation 5:

Application of the Model

HSI = SIFR x SIV4 (5 )

Summary of model variables. Four habitat variables are used in this

model to estimate habitat suitability for breeding greater sandhill cranes.

The variables attempt to characterize the importance of an evaluation site in

terms of wetland classification, water regime, percent wetland coverage, and

size (Figure 6). Definition of habitat variables and suggested measurement

techniques (Hays et al. 1981) are presented in Figure 7. Estimates for all

four variables can be obtained from good qual ity aerial photographs that have

had their wetlands classified according to Cowardin et al. (1979).

19
Habitat variable Cover types Life requisite

Wetland class ---

Water regime ---- FW'SW,HW,R'L1ld Food/reproduction ----HSI

Percent of area in

wetland ----------Entire study

area

Size of disturbance- I

free site -----

Figure 6. Relationships of habitat variables, cover types, and life

requisites to the HSI for greater sandhill crane habitat.

Habitat variable

Wetland class (description

of the general appearance

of the wetland in terms of

either the dominant vegetation life form or the

physiography and composition

of the substrate as defined

by Cowardin et al. 1979).

Water regime (the permanence of water in a wetland as defined by

Cowardin et al. 1979).

Percent of area in wetland

land (the area of wetland

cover types in the evaluation area divided by the

total area).

Size of disturbance-free

site (the area of all

cover types potentially

usable by cranes that is

at least 100 m from any

existing or proposed roadway).

Cover types

FW, SW ,HW , R, L

FW,SW,HW,R,L

All

All

Suggested techniques

Remote sensing,

on-site inspection,

National Wetland

Inventory maps

Remote sensing,

on-site inspection,

National Wetland

Inventory maps

Remote sensing,

planimeter, dot grid,

on-site inspection,

National Wetland

Inventory maps

Remote sensing,

planimeter, dot grid,

on-site inspection,

National Wetland

Inventory maps

Figure 7. Definitions of variables and suggested measurement techniques.

20
Example application. Stern et al. (1987) recently presented data for

Sycan Marsh, Oregon, that I have modified to exemplify model application. The

example study area occupies approximately 9,300 ha that I have classified as

an emergent wetland/upland complex. Within the emergent wetland, I have

classified 1,395 ha as semipermanently flooded, 4,650 ha as seasonally flooded,

and 1,860 ha as temporarily flooded. There are 1,395 ha of upland designated

as agricultural (grassland) for this exercise. I have assumed that the entire

9,300 ha are usable by greater sandhi 11 cranes because no roads currently

exist 'in the study area.

The HSI for this example study area can be determined by incorporating

the above information into equations 1-4. Only one wetland class occurs on

the study area, emergent wetland (SIVI = 1.0), but three different water

regimes (SIV2) are represented. The wetland quality index (equation I),

therefore becomes [(1.0 x 1,395) + (0.89 x 4,650) + (0.45 x 1,860)J/7,905, or

WQI =0.81. Because some uplands occur on the study area, WQI is modified by

equation 2 to yield TWQI =0.69. The single upland cover type in this example

receives an upland value of 1.0 (equation 3); UV is then combined with TWQI in

equation 4 to obtain an estimate of study area suitability for food/

reproduction (SIFR =0.85). Because the study area is >200 ha, equation 5 is

not required; HSI = SIFR.

Model assumptions. This model was developed from information obtained

from the published literature, reports, and communications with professional

biologists familiar with the species and its habitat requirements. The model

attempts to identify those biological relationships assumed most important in

explaining habitat potential, and then attempts to convert those relationships

into algorithms that yield a single index of habitat suitability ranging in

value from 0.0 to 1.0. This index is intended for use in land-use planning

where the primary objective(s) involves comparisons of habitat potential

between sites at the same point in time, or for the same site at different

points in time. Correspondence between model output and short-term estimates

of density, productivity, or other population parameters dependent on factors

not addressed in this model should not be expected.

The model assumes that optimum habitat conditions for nesting can be

supplied by extensive wetland/upland complexes such as those presently existing

at Malheur, Grays Lake, and other large National Wildlife Refuges and State

Wildlife Management Areas throughout the current breeding range of the greater

sandhill crane. Optimum is defined by factors that attempt to maximize the

number of breeding pairs, and nests, per unit area under management.

A management strategy that attempts to maximize breeding pairs and nests,

however, may also increase the probability of predation, disease, or other

density dependent mortality factors detrimental to local crane populations.

Predation rates, for example, can be high in some local populations. A

composite nest success of 29.8% was estimated at Sycan Marsh, Oregon, over a

4-year period, but annual recruitment averaged only 4.5~~ (Stern et al. 1987).

This is the same marsh that was used to pattern the example model application

in the preceding section, which produced an HSI of 0.85. The model presented

in this report was developed to characterize habitat suitability in terms of

21
maximum numbers of nesting pairs on large contiguous wetland/upland complexes;

but it does not address nest success or recruitment, which are different

performance measures and management objectives. In fact, there appears to be

a positive correlation between territory size and the number of pairs successfully fledging two colts in the Great Lakes States (Crete and Grewe 1981).

Individual s interested in evaluating nest success or potential recruitment

should not expect relevant output when using this model.

The model assumes that large areas (~200 ha) supporting a mixture of

semi permanent ly fl ooded emergent wetlands and agri cultura1 1and possess the

potenti alto supply optimum 1eve1s of the food/reproduction requi rements for

greater sandhill cranes. The model addresses the influences of human activity

by excluding all cover types within 100 m on either side of existing or

proposed roadways from consideration as crane habitat. No allowances are made

for the potential screening effect of vegetation interposed between potential

crane-use areas and roadways. Users should note that cranes are adaptable

and, at least in the Great Lakes States, appear to be using smaller wetlands

and becoming more tolerant of human activities as the populations of both

species increase (Bennett and Nauman 1978; Hoffman 1983).

SOURCES OF OTHER MODELS

The Colorado Division of Wildlife has investigated the potential for

reintroduction of greater sandhill cranes into historic nesting areas within

the State (Geduldig 1979). The most important criteria identified from

occupied sites in northern Colorado were freedom from human disturbance,

elevation below 2,896 m, and potential food resources within 0.4 km of willowlined drainages carrying water through June (Bieniasz 1978). Some of the

habitat criteria used to evaluate introduction sites included elevation

«2,896 m), spring snow accumulation and distribution along willow-lined

drainages, habitat type (willows, wet meadows, marsh), size of area, adjacent

cover types (timber, sagebrush), and potential impact from fishing, hiking,

and livestock grazing [Bieniasz (1978) observed that cranes abandon sites used

by large flocks of sheep]. No numeric values were assigned to these criteria.

A pattern recognition model (Williams et al. 1977) developed for greater

sandhill cranes in southeastern Idaho uses conditional probabilities to relate

observed habitat patterns to the potential of a site to support high

(6.2 pairs/km2 ) or low (0.4 pairs/km2 ) breeding crane densities (Wilson 1983).

Evaluation criteria include the presence and size of both wet meadow and

upland dry meadow, the length of roadway within 400 m of wet meadow, and the

relative abundance of willow within the evaluation site. Wilson's (1983)

model permits the retention of some habitat value as the length of roadway

within 400 m of a wet meadow increases; the model presented in this document

assumes no habitat value within 100 m of any roadway.

22
REFERENCES

Bennett, A.J. 1978.

eastern Wisconsin.

Ecology and status of greater sandhill cranes in southM.S. Thesis, Univ. Wisconsin, Stevens Point. 110 pp.

Bennett, A.J., and L.E. Nauman. 1978. Summer populations of sandhill cranes

in southwestern Wisconsin, 1976-77. Passenger Pigeon 40(1):349-357.

Bieniasz, K.A. 1978. Biology of the greater sandhill crane in Routt County,

Colorado. M.A. Thesis, Univ. Northern Colorado, Greeley. 72 pp.

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of wet 1ands and deepwater habi tats of the Un i ted States. U. S. Fi sh Wi 1dl .

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23
Ha 1bei sen, M. R. 1980.' Numbers and habitat preferences of greater sandhill

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-----;;8=8"-;;(3'""')----;:5=0"3----;:-5 04.

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24
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26
50272 ·lftl

REPORT DOCUMENTATION II. REPORT NO. 12-

PAGE ~iological Report 82(10.140)

.. Title .nd Subtitle

t~Habitat Suitability Index Models: Greater Sandhill Crane

\.'\.

7. Author(.)

Michael J. Armbruster

t. Perform'n. Orpnlz.tlon N.me .nd Add,.•• Natlona I t.CO logy center

U.S. Fish and Wildlife Service

Drake Creekside One Bldg.

2627 Redwing Rd.

Fort Collins, CO 80526-2899

12. Sponsorln. Orpnlutlon N.me .nd Add,... Na tiona1 Ecology Center

Research and Development

Fish and Wildlife Service

Department of the Interior

Washinqton, DC 20240

15. Supplement.ry Not..

II. Abstract (limit: 200 _rdS)

3. Recipient". Acee..lon No.

5. Report Dete

June 1987

L Performln. O,..nlzetlon Rept. No.

10. Project/T••k/Work Unit No.

11. Contract(C) or Gntnt(G) No.

lc)

(G)

13. Type of Report .. Period Covered

14.

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

Suitability Index (HSI) model for the greater sandhill crane (Grus canadensis tabida).

The model consolidates habitat use information into a framework appropriate for field

application, and is scaled to produce an index between 0.0 (unsuitable habitat) and , 1.0 (optimum habitat). HSI models are designed to be used with Habitat Evaluation

Procedures previously developed by U.S. Fish and Wildlife Service.

17. Doc:ument An.lysls •• Dnc:rlptont

Birds

Wildlife

Habitabil ity

Mathematical models

II. Identlflers/Open·Ended Term.

Greater sandhill crane

Grus canadensis tabida

Habitat suitability

I -, Co COSATI Field/Group

• .L Avall.bllity St.tement

Release unlimited

(5. ANSI-Z39.18)

19. Security CI••• (This Report)

Unclassified

20. security CI••• (Thl. P••e)

Unclassified

S.. Instruction. on Reve,.e

21. No. of P....

26

22. Price

OPTIONAL FORM 272 (4-77)

(Formerly NTI~5)

Dep.rtment of Commerce
Take Pride in America

Preserve OurNatural Resources

DEPARTMENT OF THE INTERIOR

u.s. FISH AND WILDLIFE SERVICE

As the Nation's principal conservation agency, the Department of the Interior has responsibility for most of our .nat ionally owned public lands and natural resources. This includes

fostering the wisest use of our land and water resources, protecting our fish and wildlife,

preserving the-environmental and cuttural'values of our national parks and historical places,

and providing for the enjoyment of life through outdoor recreation. The Department assesses our energy and mineral resources and works to assure that their development is in

the best interests of all our people. The Department also has a major responsibility for

American Indian reservation communities and for people who live in island territories under

U.S. administration.