Biological Services Program

and

Division of Ecological Services

FWS/OBS-8211 0.19

JULY 1982

HABITAT SUITABILITY INDEX MODELS:

GRAY SQUIRREL

___ish and Wildlife Service

SK .8. Department of the Interior

361

.U54

10.19
The Biological Services Program was established within the U.S. Fish

and Wildlife Service to supply scientific information and methodologies on

key environmental issues that impact fish and wildlife resources and their

supporting ecosystems. The mission of the program is as follows:

• To strengthen the Fish and Wildlife Service in its role as

a primary source of information on national fish and Wildlife resources, particularly in respect to environmental

impact assessment.

• To gather, analyze, and present information that will aid

decisionnakers in the ide·ntification and resolution of

problems associated with major changes in land and water

use.

• To provide better ecological information and evaluation

for Department of the Interior development programs, such

as those relating to energy development.

Information developed by the Biological Services Program is intended

for use in the planning and decisionmaking process to prevent or minimize

the impact of development on fish and wildlife. Research activities and

technical assistance services are based on an analysis of the issues, a

determination of the decisionmakers involved and their information needs,

and an evaluation of the state of the art to identify information ~aps

and to determine priorities. This is a strategy that wll1 ensure that

the products produced and disseminated are timely and useful.

Projects have been initiated in the following areas: coal extraction

and conversion; power plants; geothermal, mineral and oil shale development; water resource analysis, including stream alterations and western

water allocation; coastal ecosystems and Outer Continental Shelf development; and systems inventory, including National Wetland Inventory, habitat classification and analysis, and information transfer.

The Biological Services Progra.m consists of the Office of Biological Services in Washington, p.e., which is responsible for overall planning and

management; National Teams, which provide the Program's central scientific

and technical expertise and arrange for contracting biolo~ical services

studies with states, universities, consulting firms, and others; Regional Staffs, who provide a 1ink to problems at the operating level; and staffs at

certain Fish and Wildlife Service research facilities, who conduct in-house

research studies.

This model is designed to be used by the Division of Ecological Services in conjunction with the Habitat Evaluation Procedures.
FWS/OBS-82/10.19

July 1982

HABITAT SUITABILITY INDEX MODELS: GRAY SQUIRREL

by

Arthur W. Allen

Habitat Evaluation Procedures Group

Western Energy and Land Use Team

U.S. Fish and Wildlife Service

Drake Creekside Building One

2625 Redwing Road

Fort Collins, CO 80526

Western Energy and Land Use Team

Office of Biological Services

Fish and Wildlife Service

U.S. Department of the Interior

Washington, DC 20240
This report should be cited as:

Allen, A. W. 1982. Habitat suitability index models: gray squirrel. U.S.

Dept. Int., Fish Wildl. Servo FWS/OBS-82/10.19. 11 pp.
PREFACE

This document is part of the Habitat Suitability Index (HSI) Model Series

(FWS/OBS-82/10), 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. The habitat use information provides

the foundation for HSI models that follow. In addition, this same information

may be useful in the development of other models more appropriate to specific

assessment or evaluation needs.

The HSI Model Section documents a habitat model and 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 application information includes descriptions of the geographic ranges and seasonal

application of the model, its current verification status, and a listing of

model variables with recommended measurement techniques for each variable.

In essence, the model presented herein is a hypothesis of species-habitat

relationships and not a statement of proven cause and effect relationships.

Results of model performance tests, when available, are referenced. However,

models that have demonstrated reliability in specific situations may prove

unre 1i ab1e in others. For thi s rea son, feedback is encouraged from users of

this model concerning improvements and other suggestions that may increase the

utility and effectiveness of this habitat-based approach to fish and wildlife

planning. Please send suggestions to:

Habitat Evaluation Procedures Group

Western Energy and Land Use Team

U.S. Fish and Wildlife Service

2625 Redwing Road

Ft. Collins, CO 80526

iii
CONTENTS

Page

PREFACE iii

ACKNOWLEDGMENTS v

HABITAT USE INFORMATION 1

Genera 1 1

Food 1

Water 2

Cover 2

Reproduct ion 3

Interspersion..................................................... 3

Special Considerations............................................ 3

HABITAT SUITABILITY INDEX (HSI) MODEL.................................. 3

Model Applicability..... 3

Model Description................................................. 4

Model Relationships............................................... 6

Appl ication of the Model 8

SOURCES OF OTHER MODELS 10

REFERENCES .. ,.......................................................... 10

iv
ACKNOWLEDGMENTS

We gratefully acknowledge F. S. Barkalow and C. M. Nixon for their review

of this habitat model. The cover of this document was illustrated by Jennifer

Shoemaker. Word processing was provided by Carolyn Gulzow and Dora Ibarra.
GRAY SQUIRREL (Sciurus carolinensis)

HABITAT USE INFORMATION

General

The gray squirrel (Sciurus carolinensis)inhabits hardwood and mixed

hardwood-coniferous forests (Uhlig 1955; Golley 1962). Although they may

occur in a variety of forested habitat types, large, densely forested areas

are preferred (Taylor 1974).

Food

Fruits, floral parts, buds, bark, roots, fungi, and animal matter are

seasonally important foods for the gray squirrel (U.S. Forest Service 1971).

The annual diet of the gray squirrel in Missouri included 97 plant and 47

animal foods (Korschgen 1981). Eighteen of the plant items contributed 86.8%

of the total food volume. Mast was the principle food item during the winter

months. Hickories (Carya spp.), pecan (~. illinoensis), black walnut (Juglans

nigra), and red mulberry (Morus rubra) were used to a much greater extent than

indicated by their percentage of the forest composition. Hickory mast was

selected most often by squirrels in Ohio (Nixon et al. 1968).

A significant relationship existed between the annual seed crop and

subsequent squirrel densities in an Ohio study (Nixon et al. 1975). The

survival of summer-born juvenile squirrels was drastically reduced when the

seed crop fell below 145.7 kg of sound seed per ha (130 lb/acres), because of

the increased competition for mast from older individuals and other wildlife

species. A mast production greater than 168 kg/ha (150 lb/acres) is needed to

sustain reasonably high squirrel densities. Approximately 8.5 m2 (71.8 f t ")

of basal area in trees of seed producing size [~ 25.4 cm (10 in)] will produce

this amount of seed.

A variety of mast produci ng species should be present over a range of

sites in order to minimize the effect of crop failure (Nixon et al. 1975).

Mast crops vary by species, age of tree, soil and weather influences and seed

production by individual trees (Spurr and Barnes 1980). Weather is unlikely

to have a major impact on seed production ina forest that conta ins several

tree species because the time of flowering will vary by species.

Large, dominant trees with exposed, sunlit crowns are the primary seed

producers in closed stands (Spurr and Barnes 1980). Smaller trees with shaded

crowns will produce few, if any, seeds.

1
Water

Eastern gray squirrels can satisfy water needs from free water or succulent plant materials (U.S. Forest Service 1971). However, pregnant and lactating females often use free water (Barkalow pers. comm.). Therefore, free

water should be available within the normal home range.

Cover

Optimum gray squirrel habitat in Illinois was a closed canopy forest with

a well developed understory (Nixon et al. 1978). The squirrels were most

often associated with extensive, ungrazed forests with a predominance of trees

in the sawtimber size class [dbh 22.8 cm (9 inches)]. Important tree species

were sugar maple (Acer saccharum), white oak (Quercus alba), elm (Ulmus spp.),

and black oak (Q. YelUtina). These species indicate climax, or near climax,

conditions on upland sites in Illinois. Gray squirrels were absent from

forests in early successional stages containing tree species such as osage

orange (Maclura pomifera), shagbark hickory (~. ovata), hackberry (Celtis

occidental is), and hawthorn (Crataegus spp).

Tree cavities are almost always used by gray squirrels for rearing their

winter litters (Barkalow pers. comm.). Although leaf nests are often used by

fox squirrels, they are seldom used by gray squirrels (Nixon pers. comm.).

The most critical need for dens is for rearing litters and winter shelter

(Nixon et al. 1968). At least one den per 0.8 ha (2 acres) was recommended as

necessary to provide enough winter shelter for gray squirrels (Sanderson

1975). Two to five den trees per 0.4 ha (2 to 5/acre) are optimum (Brown and

Yeager 1945; U.S. Forest Service 1971). Forest stands occupied by gray

squirrels in Illinois never averaged less than 6 cavities/ha (2.4/acre) (Nixon

et al. 1978). The average number of cavities was twice the number available

in stands that were not occupied by gray squirrels.

Even-aged stands of hardwoods less than 30 to 40 years old do not produce

sufficient mast or cavities to support gray squirrel populations (U.S. Forest

Service 1971). Hardwood stands more than 60 years old are optimum gray

squirrel habitat.

Ash (Frax i nus spp.), elm, oaks, hi ckori es, beech (Fagus spp.), cypress

(Taxodium distichum), sycamore (Platanus occidentalis), sassafras (Sassafras

albidum), and basswood (Tilia spp.) are most often used as den trees by gray

squirrels in the eastern United States (Goodrum 1937; Nixon 1968). Blackgum

(Nyssa sylvatica), beech, and maple (Acer spp.) produced most of the cavities

suitable for gray squirrels in Georgia~though oaks, which are more common,

may be the most important trees in terms of providing shelter (Golley 1962).

Sassafras, elm, beech, and sugar maple in Illinois contained more cavities

than expected based on their relative abundance (Nixon et al. 1980). White

oak and black walnut contained significantly fewer cavities than expected.

Gray squirrels in West Virginia usually nested in live trees with a dbh

of at least 40.0 cm (15.7 inches) (Sanderson et al. 1975). Eighty-eight

percent of gray squirrel dens in eastern Texas were in trees with a dbh of at

least 30.5 cm (12 inches) (Baker 1944).

2
Reproduction

The reproductive requirements of the gray squirrel are assumed to be

identical with the cover requirements described above.

Interspersion

The home range of the gray squirrel in Missouri was from 4 to 16 ha (10

to 40 acres) (Schwartz and Schwartz 1959). The mean mi ni mum home range for

gray squirrels in Virginia was 0.49 ha (1.2 acres) (Doebel and McGinnes 1974).

Male gray squirrels generally have a larger range than do females, and their

range often overlaps with those of other adult squirrels (Bakken 1959; Cordes

and Barkalow 1972). Breeding females defend their territory against other

female gray squirrel s (Nixon et al. 1975) and are more sedentary than adult

males or subadults (Nixon et al. 1980). Therefore, they are more susceptible

to habitat changes that affect the availability of denning sites and food.

Areas occupied by gray squirrels in northern and central Illinois were at

least 20% forested (Nixon et al. 1978).

Special Considerations

The ranges of fox and gray squirrels overlap through most of the eastern

United States (Bakken 1952 cited by Taylor 1974). Coexistence of the two

species occurs mostly in the western and northern portions of the ranges of

both species (Bakken 1952, cited by Taylor 1974). Although the two species

may inhabit the same general area, they tend to concentrate in slightly different habitats. Gray squirrels prefer large dense stands of hardwoods with a

dense understory, whereas fox squirrels generally prefer open woodland habitats

with little understory vegetation (Taylor 1974). Gray squirrels in Texas were

more common in poorly drained lowland areas, while fox squirrels were more

frequent in upland and well drained bottomland habitats (Goodrum 1937).

Differences in habitat preference and foraging behavior are reflected in the

foods eaten. Fox squirrels in Missouri commonly inhabit open forests, forest

edges, woodlots, and fence rows where oak-hickory mast (52.2% of the annual

diet) is supplemented with corn and other foods associated with these habitats

(Korschgen 1981). Gray squi rrel s occupy dense forests with nearly closed

canopies and abundant ground cover, and rely more on oak-hickory mast (73.3%

of the annual diet).

HABITAT SUITABILITY INDEX (HSI) MODEL

Mode 1 App 1i cabi 1ity

Geographic area. This model is applicable throughout the geographic

range of the species.

Season. This model will produce HSI values for year-round habitat needs

of the gray squirrel.

3
Cover types. This model is intended to evaluate gray squirrel habitat in

the following cover types (terminology follows that of U.S. Fish and Wildlife

Service 1981): Deciduous Forest (OF) and Deciduous Forested Wetland (DFW).

Minimum habitat area. Minimum habitat area is defined as the minimum

amount of contiguous habitat that is required before an area will be occupied

by a species. The mean minimum home range for the gray squirrel is at least

0.49 ha (1.2 acres). For purposes of this model, it is assumed that a habitat

of less than 0.4 ha (1 acre) will provide no suitability; the HSI will equal

0.0 in such areas.

Verification level. This model was reviewed by F. S. Barkalow, North

Carolina State University, and C. M. Nixon, Illinois Institute of Natural

Resources. Improvements suggested by these revi ewers were incorporated into

this model.

Model Description

Overview. All habitat requirements of the gray squirrel can be satisfied

wi thi n deci duous forests or deci duous forested wetlands. Therefore, thi s

model treats the gray squirrel as using only these cover types, and habitat

evaluation based on this model only considers the quality of life requisites

provided by deciduous forested cover types. The cover and reproductive needs

of the gray squirrel are assumed to be identical. It also is assumed that the

availability of water will never be more limiting than the winter food or

cover/reproduction potential of the site.

The following sections document the logic and assumptions used to translate habitat information for the gray squirrel to the variables and equations

used in the HSI model. Specifically, these sections cover: (1) identification

of variables used in the model; (2) definition and justification of the suitability levels of each variable; and (3) description of the assumed relationships between variables.

Figure 1 illustrates the relationships of habitat variables, life

requisites, and cover types for the gray squirrel.

Winter food component. A wide variety of vegetative food is consumed by

the gray squirrel during the spring and summer. The late summer, fall, and

winter diet consists mainly of hickory, beech, and oak mast. It is assumed

that the availability of fall and winter food will always be more critical

than the avail abi 1i ty of spri ng and summer food. Mi xed forest stands wi11

provide a more stable winter food supply than stands that consist of only one

mast producing species. A forest stand should have at least 8.5 m2 per hectare

(36 ft 2/acre) of basal area of seed producing trees [z 25.4 cm (10 inches)

dbh] . It is assumed that the optimum dens i ty of mast trees is between 40 to

60% canopy closure. When tree canopy closure is greater than 60% mast quality

and quantity decreases because tree crowns are shaded by adjacent trees.

Winter food quality is a function of the density and species diversity of

mast producing trees of the proper size in the stand. Habitats which lack

trees that produce hard mast will have no winter food for gray squirrels.

4
Habitat variables Life requisites Cover types

Percent canopy closure of trees that

p roduce mast (e.g., oak, hickory, walnut, pecan, and beech) which are greater than 25.4 cm (10 inches)

dbh.

Diversity of trees that produce hard mast

Winter food

Deciduous forest

Deciduous forested

wetland

____ HSI

Cover/reproduction

Percent shrub crown coverPecceot tcee c,oopy Clo,uce~

Average dbh of overstory trees

en

Figure 1. Relationship of habitat variables, life requisites, and cover types in the

gray squirrel HSI model.
Species diversity in a forest contributes to a stable food supply. Optimum

conditions are assumed to exist when the forest stand contains at least four

species of trees that produce hard mast.

Cover/reproduction component. Dense forest stands that have overstory

trees with large diameter, and a moderately dense understory provide optimum

cover for gray squirrels. Gray squirrels are almost entirely dependent on

tree cavities for winter cover and litter rearing. Forest stands dominated by

mature to overmature trees are assumed to contain enough cavities to meet the

cover requirements of the gray squirrel. Optimum conditions are believed to

occur when tree canopy closure ranges from 40 to 75% and the average dbh of

overstory trees is at least 38.1 cm (15 inches). Overstory trees with an

average dbh of 12.7 cm (5 inches) or less indicate a forest stand that is too

young to contain the cavities required by gray squirrels.

The density of shrubby understory vegetation in a forest will influence

the cover/reproduction value for gray squirrels. Optimum understory shrub

crown cover is assumed to range from 20 to 30%. Forest stands that do not

have a shrub understory will be of slightly less value than stands with optimum

shrub density. When shrub density increases above 30%, the cover/reproduction

value of the stand will decrease, regardless of the percent closure or size of

overstory trees. It is assumed that, although understory shrub density may

greatly reduce the value of a stand value as gray squirrel cover/reproduction

habitat, it will never completely limit the ability of the stand to provide

cover.

Model Relationships

Suitability Index (SI) graphs for habitat variables. This

tains suitability index graphs that illustrate the habitat

described in the previous section.

section conrelationships

Cover

type

DF,DFW

Variable

Percent canopy closure

of trees that produce

hard mast (e.g., oak,

hickory, walnut, pecan,

and beech) which are

25.4 cm (10 inches)

dbh.

6

x

(1)

-g 0.8 ......

......

~06

.....

.0

co 0.4

+J

.....

::l

(/}0.2

25 50

%

75 100
1.0

DF,DFW V2 Diversity of tree species

that produce hard mast. x

0.8 - s:::

A) None present .......

B) 1 species present ~0.6 -

C) 2 species present

D) 3 species present 0.4 - E) 4 or more species +J

present .,....

::::l

VlO.2

A B c o E

DF,DFW Percent tree canopy

closure.

Tree Species Diversity

X

OJ

-g 0.8

>,

.~ 0.6

.,....

.0

.B 0.4 .,....

::::l

Vl 0.2

25 50

%

75 100

DF,DFW Average dbh of overstory

trees.

1. 0 +-0-..............................-....-......................-+-0------1-

X

OJ

-g 0.8

.,....

~0.6

-e--

.0.B 0.4 'r-

::::l

Vl 0.2

7

12.7

5

25.4

10

38.1

15

50.8

20

(cm)

(inch)
DF,DFW Percent shrub crown

cover. X

<LJ

-g 0.8 .......

.....

~0.6 r--

.....

..0

.;:l0.4

.....

::5

(/)0.2

25 50

%

75 100

Equations. In order to obtain life requisite values for the gray

squirrel, the 5I values for appropriate variables must be combined through the

use of equations. A discussion and explanation of the assumed relationships

between variables was included under Model Description, and the specific

equations in this model were chosen to mimic these perceived biological relationships as closely as possible. The suggested equations for obtaining life

requisite values for the gray squirrel are presented Figure 2.

Life Requisite

Winter food

Cover/reproduction

Cover Type

DF,DFW

DF,DFW

Equations

Figure 2. Equations for determining life requisite values by

cover type for the gray squirrel.

H5I determination. The H5I for the gray squirrel will equal the lowest

of the values obtained for Winter Food or Cover/reproduction.

Application of the Model

Definitions of variables and suggested field measurement techniques (Hays

et al. 1981) are presented in Figure 3.

8
Variable (definition)

Percent canopy closure

of trees that produce

hard mast (e.g., oak,

hickory, walnut, pecan,

and beech) which are

25.4 cm (10 inches)

dbh [the percent of the

ground that is shaded by

a vertical projection of

the canopies of trees which

produce a hard shelled fruit

and have a dbh of at least

25.4 cm (10 inches)].

Diversity of tree species

that produce hard mast

(the number of tree

species present in the

stand or sample site

that produce hard mast).

Percent tree canopy

closure [the percent of

the ground surface that

is shaded by a vertical

projection of the canopies

of all woody vegetation

> 5.0 m (16.5 ft) tall].

Average dbh of overstory

trees [the average diameter

at breast height (1.4 m;

4.5 ft) above the ground

of those trees that are

80 percent of the height

of the tallest tree in the

stand].

Percent shrub crown cover

[the percent of the ground

surface that is shaded by a

vertical projection of the

canopies of woody vegetation

< 5 m (16.5 ft) tall].

Cover types

DF,DFW

DF,DFW

OF ,DFW

DF,DFW

DF,DFW

Suggested technique

Calculated area of

plant using crown

diameter on strip

quadrat

Transect, tally

Transect, line intercept, remote sensing

Cruise for tallest

tree, sample with

optical range finder

and Biltmore stick on

strip quadrat

Transect, line intercept

Figure 3. Definitions of variables and suggested measurement

techniques.

9
SOURCES OF OTHER MODELS

No other habitat models for the gray squirrel were located.

REFERENCES

Baker, R. H. 1944. An ecological study of tree squirrels in eastern Texas.

J. Mammal. 25(1):8-24.

Bakken, A. 1952. Interrelationships of Sciurus carolinensis (Gmelin) and

Sciurus niger (Linneaus) in mixed populations. Ph.D. Diss., Univ. Wise.,

Madison. 188 pp. Cited by Taylor 1974.

1959. Behavi or of gray squi rre 1s . Proc. Southeastern Assoc.

Game and Fish Commissioners 13:393-407.

Barkalow, F. S., Jr. Personnal communication. Zoology Dept., North Carolina

St. Univ., Raleigh.

Brown, L. G., and L. E. Yeager. 1945. Fox squirrels and gray squirrels in

Illinois. Illinois Nat. Hist. Surv. Bull. 23(5):449-536.

Cordes, C. L., and F. S. Barkalow. 1972.

Car 0 1ina gray squi r r e 1 popu1at ion .

Fish Commissioners 26:124-135.

Home range and dispersal in a North

Proc. Southeastern Assoc. Game and

Doebel, J. H., and B. S. McGinnes. 1974. Home range and activity of a gray

squirrel population. J. Wildl. Manage. 38(4):860-867.

Golley, F. B. 1962. Mammals of Georgia, a study of their distribution and

functional role in the ecosystem. Univ. Georgia Press, Athens. 218 pp.

Goodrum, P. 1937. Notes on gray and fox squirrels of eastern Texas. Trans.

N. Am. Wildl. Conf. 2:449-504.

Hays, R. L., C. S. Summers, and W. Seitz. 1981. Estimating wildlife habitat

variables. U.S.D.l. Fish and Wildlife Service. FWS/OBS-81/47. 173 pp.

Korschgen, L. J. 1981. Foods of fox and gray squirrels in Missouri. J.

Wildl. Manage 45(1):260-266.

Nixon, C. M. Personnal communication (letter dated 2 October 1981). Illinois

Inst. Nat. Resour., Champaign, IL.

1968. Squirrel management guidelines for wildlife areas. Ohio

Dept. Nat. Resour., Div. Wildl. Inservice Document 55. 8 pp.

Nixon, C. M., S. P. Havera, and R. E. Greenberg.

abundance of the gray squirrel in Illinois.

Biol. Notes 105. 55 pp.

10

1978. Di stribution and

Illinois Nat. Hist. Surv.
Nixon, C. M., S. P. Havera, and L. P. Hansen. 1980. Initial response of

squirrels to forest changes associated with selection cutting. Wildl.

Soc. Bull. 8(4):298-306.

Nixon, C. M., M. W. McClain, and R. W. Donohoe. 1975. Effects of hunting and

mast crops on a squirrel population. J. Wildl. Manage. 39(1):1-25.

Nixon, C. M., D. M. Worley, and M. W. McClain. 1968. Food habits of squirrels

in southeast Ohio. J. Wildl. Manage. 32(2):294-304.

Sanderson, H. R. 1975. Den-tree management for tree squirrels. Wildl. Soc.

Bull. 3(3):125-131.

Sanderson, H. R., W. M. Healy, J. C. Po"lk, J. D. Gill, and J. W. Thomas.

1975. Gray squirrel habitat and nest-tree preference. Proc. Southeastern

Assoc. Game and Fish Commissioners 29:609-616.

Schwartz, C. W., and E. R. Schwartz. 1959. The wild mammals of Missouri.

Univ. Missouri Press and Missouri Dept. of Conserv., Columbia. 341 pp.

Spurr, S. H., and B. V. Barnes. 1980. Forest ecology. John Wiley and Sons.

New York, New York. 687 pp.

Taylor, G. J. 1974. Present status and habitat survey of the Delmarva fox

squirrel (Sciurus niger cinereus) with a discussion of reasons for its

decline. Proc. Southeastern Assoc. Game and Fish Commissioners

27:278-289.

Uhlig, H. G. 1955. The gray squirrel, its life history, ecology, and population characteristics in West Virginia. West Virginia Conserv. Comm.

182 pp.

U.S. Fish and Wildlife Service. 1981.

habitat suitability index models.

Div. Ecol. Servo n.p.

Standa rd s for the deve 1opment of

103 ESM. U.S.D.l. Fish Wildl. Serv.,

U.S. Forest Service. 1971. Wildlife habitat management handbook. U.S.D.A.

For. Serv., Southern Region. FSH 2609.23R. n.p.

11
5027'2 101 .

REPORT DOCUMENTATION I 1. REPORT NO. I 2. I 3. Recipient's AccRslon No.

PAGE i FWS/OBS-82/10.19 I

I I

•• Title and Subtitle i 5. Report Date

Habitat Suitabi 1i ty Index Models: Gray Squirre1 Julv 1982

6.

7. Author(

Arthur

s)

W. Allen 8. Performinll O,.anizatlon Rept. No.

•

9. Performinll O,.anization Name and Address Habitat Evaluation Procedures Group 1 10• Project/Task/Work Unit No.

Western Energy and Land Use Team I

I

U.S. Fish and Wildlife Service r11. Contraet(C) or Grant(Gl No.

Drake Creekside Building One I (el

2625 Redwing Road , (Gl

Fort. rollins rolorado RO!)~fi

12. Sponsorinll Organization Name and Address Western Energy and Land Use Team 13. Type of ReQQrt & Period Covered

Office of Biological Services

Fish and Wildlife Service

U.S. Department of the Interior I 14. I

Washington, DC 20240 I 15. Supplementary Notes

·11i. Abstract (Limit: 200 words)

Habitat preferences and species characteristics of the gray squirrel (Sciurus carolinensis) are described in this publication. It is one of a series of Habitat Suitability Index (HSI) models and was developed through an analysis of available scientific data

on the species-habitat requirements of the gray squirrel. Habitat use information is

presented in a review of the literature, followed by the development of a HSI model.

The model is presen ted in three forma ts: graph i c. word. and rna themati ca 1. Suita bi 1ity ,

index graphs quantify the species-habitat relationship. These data are then synthesized

into a model which is designed to provide information for use in impact assessment and

habitat management activities.

I

17. Document Analysis a. Descriptors

ltJi 1dl ife Mathematical models 

Anima1 behavior Mammals

Animal ecology Squirrels

Habitabi 1ity 

O. Identlfiers/OQen-Ended Terms 

Gray squirrel Habitat management Impact assessment

Sciurus carolinensis Habitat suitability index models

Habitat suitability Habitat requirements Habitat preference Species-habitat relationships 

c. COSATI Field/Group

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Uoyd FiveHundred Building, Suite 1692

500 N.E. Multnomah Street

Portland, Oregon 97232

REGION 2

Regional Director

U.S. Fish and Wildlife Service

P.O. Box 1306

Albuquerque, ew Mexico 87103

REGION 3

Regional Director

U.S. Fish and Wildlife Service

Federal Building, Fort Snelling

TwinCities,M~ta SU 1'1

U.S. FISH AND WILDLIFE SERVICE

REGIONAL OFFICES

REGION 4

Regional Director

U.S. Fish and Wildlife Service

Richard B. Russell Building

15 SpringStreet, S.W.

Atlanta, Georgia 30303

REGION S

Regional Director

U.S. Fish and Wildlife Service

One Gateway Center

NewtonCorner, Massachusetts 02158

REGION 6

Repmal DiJ8Ctor

u.s. fitb and Wildlife Serviet

P.O. Box25486

DenverFtd.eral Center

Denver. Colorado 80225

REGION 7

Regional Director

U.S. Fish and Wildlife Semce

1011 E. Tudor Road

Anchorl., Alaska 99503
DEPARTMENT OF THE INTERIOR

u.s. FISH AND WILDLIFE SERVICE

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

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

preserving th.environmental and cultural values of our national parks and historical places,

and providing for the enjoyment of life through outdoor recreation. The Department a.,

sesses 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.