Biological Services Programand

Division of Ecological ServicesFWS/OBS·82/10.18JULY 1982

e'- e

u.evorde L .sionc 70506,

HABITAT SUITABILITY INDEX MODELS:FOX SQUIRREL

Fish and Wildlife Service

u.s. Department of the Interior

The 8iological Services Program was established within the U.S. Fishand Wildlife Service to supply scientific information and methodologies onkey environmental issues that impact fish and wildlife resources and theirsupporting ecosystems. The mission of the program is as follows:

• To strengthen the Fish and Wildlife Service in its role asa primary source of information on "4tiona1 fish and wild­life resources. particularly in respect to environmentalimpact assessment.

• To gather, analyze, and present information that will aiddecisiOMlakers in the identification and resolution ofproblems associated with major changes in land and wateruse.

• To provide better ecological information and evaluationfor Department of the Interior development programs. suchas those relating to energy development.

Information developed by the 8iological Services Program is intendedfor use in the planning and decisionmaking process to prevent or minimizethe impact of development on fish and wl1dlife. Research activities andtechnical assistance services are based on an analysis of the issues, adetermination of the decisionmakers involved and their information needs,and an evaluation of the state of the art to identify information gapsand to determine priorities. This is a strategy that will ensure thatthe products produced and disseminated are timely and useful.

Projects have been initiated in the following areas: coal extractionand conversion; po~r plants; geothermal, mineral and oil shale develop­ment; water resource analysis, including stream alterations and westernwater allocation; coastal ecosystems and Outer Continental Shelf develop­ment; and systems inventory, including National Wetland Inventory.habitat classification and analysis. and information tnnsfer.

The Biological Services Prognm consists of the Office of BiologicalServices in Washington, D.C .• which is resp,onsible for overall planning andmanagement; National Teams. which pro'vide the Program's central scientificand technical expertise and arrange for contracting biolo~ical servicesstudies with states, ~niversities, consulting firms. and others; RegionalStaffs, who provide a link to problems at the operating level; and staffs atcertain Fish and Wildlife Service research fac11ities, who conduct in-houseresearch studies.

This model ;s designed to be used by the Division of Ecological Servicesin conjunction with the Habitat Evaluation Procedures.

FWS/OBS-82/10.18July 1982

HABITAT SUITABILITY INDEX MODELS: FOX SQUIRREL

by

Arthur W. AllenHabitat Evaluation Procedures GroupWestern Energy and Land Use Team

U.S. Fish and Wildlife ServiceDrake Creekside Building One

2625 Redwing RoadFort Collins, CO 80526

Western Energy and Land Use TeamOffice of Biological Services

Fish and Wildlife ServiceU.S. Department of the Interior

Washington, DC 20240

This report should be cited as:

Allen, A. W. 1982. Habitat suitability index models: fox squirrel. U.S.Dept. Int., Fish Wildl. Servo FWS/OBS-82/10.18. 11 pp.

PREFACE

This document is part of the Habitat Suitability Index (HSI) Model Series(FWS/OBS-82/l0) , which provides habitat information useful for impact assess­ment and habitat management. Several types of habitat information areprovided. The Habitat Use Information Section is largely constrained to thosedata that can be used to derive quantitative relationships between key environ­mental variables and habitat suitability. The habitat use information providesthe foundation for HSI models that follow. In addition, this same informationmay be useful in the development of other models more appropriate to specificassessment or evaluation needs.

The HSI Model Section documents a habitat model and information pertinentto its application. The model synthesizes the habitat use information into aframework appropriate for field application and is scaled to produce an indexvalue between 0.0 (unsuitable habitat) and 1.0 (optimum habitat). The applica­tion information includes descriptions of the geographic ranges and seasonalapp1i cat i on of the mode 1, its current verifi cat i on status, and ali st i ng ofmodel variables with recommended measurement techniques for each variable.

In essence, the model presented herein is a hypothesis of species-habitatrelationships 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 proveunreliable in others. For this reason, feedback is encouraged from users ofthis model concerning improvements and other suggestions that may increase theutility and effectiveness of this habitat-based approach to fish and wildlifeplanning. Please send suggestions to:

Habitat Evaluation Procedures GroupWestern Energy and Land Use TeamU.S. Fish and Wildlife Service2625 Redwing RoadFt. Collins, CO 80526

iii

CONTENTS

Page

PREFACE iiiACKNOWLEDGMENTS v

HABITAT USE INFORMATION 1Genera 1 1Food ............................................................•. 1Water 1Cover 1Reproduct ion 2Interspersion..................................................... 2Special Considerations............................................ 2

HABITAT SUITABILITY INDEX (HSI) MODEL 3Model Applicability 3Model Description................................................. 3Model Relationships 6Appl ication of the Model 8

SOURCES OF OTHER MODELS 9

REFERENCES 9

iv

ACKNOWLEDGMENTS

We gratefully acknowledge F. S. Barkalow and C. M. Nixon for their reviewof this habitat model. Word processing was provided by Carolyn Gulzow andDora Ibarra. Cover ill ustrat ion is by Larry We 10 and ori gi nally appeared ; nMount Rainier's Mammals.

v

FOX SQUIRREL (Sciurus niger)

HABITAT USE INFORMATION

General

The fox squirrel (Sciurus niger) is the largest of the North Americantree squirrels. The species is widely distributed throughout eastern NorthAmerican and has been introduced in many portions of the West (Wright 1979).Fox squirrels also have expanded their range westward through utilization ofgallery forest habitats along major river drainages (Armstrong 1972; Wright1979).

Food

Foods consumed by the fox squirrel include mast, tree buds, insects,tubers, bulbs, roots, pird eggs, and the seeds of spring fruiting trees (Lowery1974). Winter foods are chiefly mast produced by oaks (Quercus spp.),hickories (Carya spp.), American beech (Fagus grandifolia), magnolias(Magnoliaceae spp.), gums (Hamamelidaceae spp.), and dogwoods (Cornus spp.).Agricul tura 1 crops such as corn, soybeans, oats, wheat, and frui t crops arealso readily eaten by the fox squirrel (Brown and Yeager 1945).

Water

Succulent vegetation normally satisfies the moisture requirements of foxsquirrels (Allen 1943; McConnell, pers. comm.). Water may be utilized whenpresent; however, the lack of it is not a limiting habitat factor for the foxsquirrel (U.S. Forest Service 1971).

Cover

Although fox squirrels inhabitat a wide variety of forest types, they aremost abundant in open forest stands with little understory vegetation (Taylor1974). Ideal habitat is comprised of small stands of large trees interspersedwith agricultural lands. Optimal fox squirrel habitat in Michigan was smallunits of mature oak-hickory woodland connected by small wooded strips thatserved as travel lanes for squirrels (Allen 1943). Fox squirrel habitat inOhio consisted of small, 2 to 121.4 ha (5 to 300 acres) farm woodlots(Baumgartner 1943).

Fox squirrels use leaf nests or tree cavities for shelter and litterrearing (Baumgartner 1943). However, they appear to use leaf nests more often

1

than do gray squirrels (S. carolinensis) (Bakken 1952 cited by Taylor 1974;Donohoe and Beal 1972). Fox squirrels in Ohio utilized one to three sheltersin their territory, at least one of which was a tree cavity (Donohoe and Beal1972).

Hickories, white oak (Quercus alba), scarlet oak (Q. coccinea), and beechwere the most frequently selected trees for construction of leaf nests in WestVirginia, Ohio, and Illinois (Sanderson et al. 1980). The presence of grape­vines (Vitus spp.) in a tree increased the likelihood of the trees beingselected----as-a leaf nest site. Based on the average number of leaf nestsconstructed by a fox squirrel per year, it appears that four to six canopy­reaching grapevines per hectare (1.5 to 2.3/acre) provide an adequate numberof leaf nest anchorages. Trees containing summer and winter leaf nests inOhio averaged 37.8 cm (15.1 inches) dbh and 32.8 cm (13.1 inches) dbh, respec­tively (Baumgartner 1939).

Sassafras (Sassafras albidum), sugar maple (Acer saccharum), elm (Ulmusspp.), and beech contained a significantly greater proportion of suitablecavities than expected on the basis of their abundance in Illinois (Nixonet al. 1980). In contrast, walnut (Juglans spp.) and white oak containedsignificantly fewer cavities than expected. Den trees in Ohio had an averagedbh of 53 cm (21.2 inches) and were an average of 50.9 m (58.6 yd) from thenearest woodland border (Baumgartner 1939). Eighty-eight percent of the dentrees in eastern Texas had an average dbh of 30 cm (12 inches) or more (Baker1944) .

Reproduction

The reproductive requirements of the fox squirrel are assumed to beidentical with cover requirements, as described above.

Interspersion

The home range of the fox squirrel in the Southeast is normally from 2 to4 ha (5 to 10 acres) (U.S. Forest Service 1971). The mean home range size formale and female fox squirrels in Nebraska was 7.56 ha (18.7 acres) and 3.55 ha(8.8 acres), respectively (Adams 1976). A positive relationship exists betweenfox squirrel home range size and the area of the inhabited woodlot or foreststand (Adams 1976; Nixon pers. comm.). Adult female fox squirrels are moresedentary than are adult males or subadults (Nixon et al. 1980). Therefore,adult females are more susceptible to habitat changes that affect the avail­ability of denning sites and food.

Special Considerations

Fox and gray squi rre 1 ranges overl ap throughout most of the easternUnited States (Bakken 1952 cited by Taylor 1974). Coexi stence of the twospecies is most evident in the western and northern portions of the ranges ofboth species (Bakken 1952 cited by Taylor 1974). Although the two species mayinhabit the same general area, they tend to concentrate in slightly differenthabi tats. Fox squi rre 1s prefer open woodl and habitats; gray squi rre1s typi­cally inhabit large dense stands of hardwoods with dense understory cover

2

(Taylor 1974). Gray squirrels in Texas were more common in poorly drained1owl and areas, whereas fox squi rre1s were more frequently associ ated withupland and well drained bottomland habitats (Goodrum 1938). Differences inhabitat preference and foraging behavior are reflected in foods eaten. Foxsquirrels in Missouri commonly inhabit open forests, forest edges, woodlots,and fence rows, where oak-hickory mast (52.2% of the annual diet) is supple­mented wi th corn and other foods common 1y associ ated with these habitats(Korschgen 1981). Gray squirrels occupy dense forests with nearly closedcanopies and abundant ground cover and rely more heavily on oak-hickory mast(73.3% of annual diet) than do fox squirrels.

HABITAT SUITABILITY INDEX (HSI) MODEL

Model Applicability

Geographic area. This model appears to be most applicable in the rangesof the following subspecies of the fox squirrel: s.n. rufiuenter, s.n.vu1pinus, ~.!!. 1udovicianus, and ~.!!. 1imitis (Barka1ow-pers. comm.). Sub­species inhabiting the Outer Coastal Plain Forest and Southeastern MixedForest Provi nces (Bai1 ey 1980) appear to have suffi ci ent1y different habitatrequirements to justify separate or modified habitat mode1(s).

Season. This model will produce HSI values for year-round habitat needsof the fox squirrel.

Cover types. This model is intended to evaluate fox squirrel habitat inthe following cover types (terminology follows that of U.S. Fish and WildlifeService 1981): Deciduous Forest (OF); Deciduous Tree Savanna (DTS); andDeciduous Forested Wetland (DFW).

Minimum habitat area. Minimum habitat area is defined as the minimumamount of contiguous habitat that is required before an area will be occupiedby a species. This information, as it pertains to the fox squirrel, was notfound in the literature. The home range of the fox squirrel has been reportedto range from 2 to 8 ha (5 to 20 acres). It is assumed that, if less than2 ha (5 acres) of potentially suitable habitat is available, the HSI willequal 0.0.

Verification level. This model was reviewed by F.S. Barkalow, NorthCarolina State University, and C.M. Nixon, Illinois Institute of NaturalResources. Improvements suggested by these revi ewers were incorporated intothis model.

Model Description

Overview. This HSI model for the fox squirrel considers the quality oflife requisites for the species in each cover type. Winter food and Cover/reproduction are the only life requisites considered in this model.

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

3

used in the HSI model. Specifically, these sections cover: (1) identificationof 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 fox squirrel.

Food component. A wide variety of vegetative and animal materials may beconsumed by the fox squirrel during the spring, summer, and fall. Winterfoods are comprised almost wholly of hard mast and grain. It is assumed thatthe availability of winter food will be the most limiting component of thefood requirements of the fox squirrel.

The winter food value for the fox squirrel is a funttion of hard mastproduction and, to a lesser extent, the availability of grain. Optimum foodcan be supplied by hard mast; however, grain availability may be extremelyimportant during years of little or no mast production. It is assumed thatthe potential for optimum mast production will occur where a mix of white andred oaks, hickories, walnuts, and other mast producing trees comprise at least40% of the total canopy cover of the forest or stand. Mast produci ng treesshould equal or exceed 25.4 cm (10 inches) dbh to provide optimum mast produc­tion. As tree canopy closure increases above 60%, mast quality and quantityis reduced due to suppressi on and shadi ng of tree crowns by adjacent trees.It also is assumed that grain within 200 m (220 yds) of a forest or stand willhave optimal value as a supplement to the winter diet of the fox squirrel.Available grain in excess of 200 m (220 yds) will have a lower potential as asupplement. The winter diet of fox squirrels will never be completely limitedby the absence of a source of grain. It is assumed that potential mast produc­tion is at least three times as important in supplying winter food for the foxsquirrel as is the availability of grain.

Cover and Reproductive Component. Fox squirrels inhabitat a variety offorest types. However, they are most abundant in open forest stands withsparse understory vegetation.

Although fox squirrels commonly utiliz~ leaf nests for shelter and litterrearing, the presence of tree cavities will increase the quality of thehabitat. It is assumed that the physical structure of a forest stand is ani ndi cat i on of the avail abil i ty of tree cavi ties. Forest stands domi nated bymature to overmature trees are assumed to provide cavities and a sufficientnumber of sites for leaf nests to meet the cover requirements of the species.Overstory trees which have an average dbh of 38.1 cm (15 inches) or larger areassumed to provide adequate cover and reproductive habitat. Optimum treecanopy closure is assumed to range from 20 to 60%. A canopy closure of lessthan 20% will indicate less suitable habitat, as will tree density exceeding60%. Understory vegetation comprised of shrubs may decrease habitat qual ityfor the fox squirrel. Optimum conditions are assumed to occur whenihe shrubcrown closure is 30% or less. Habitat quality will decrease as the shrubdensity increases above 30%, regardless of tree canopy closure and overstorysize. A shrub density of 100% is assumed to be indicative of habitat with nosuitability for fox squirrels.

4

Habitat variables Li fe regu i sites Cover tYpes

Distance to available grain

Percent canopy closure of treesthat produce hard mast (e.g.,oak, hickory, walnut, pecan,beech) which are greaterthan or equal to 25.4 cm(10 inches) dbh

-------HSI

Deciduous ForestDeciduous Tree

SavannaDeciduous Forested

Wet Iand

Wi nter food

Cover and reproduction

dbh of overstory t~re::

tree canopy closure ----------:::::~

shrub crown coverPe rcent

Average

Percent

U1

Figure 1. The relationship of habitat variables, life requisites,and cover types to the HSI for the fox squirrel.

Model Relationships

Suitability Index (SI) curves for habitat variables. This sectioncontains suitability index graphs that illustrate the habitat relationshipsdescribed in the previous section.

Cover~

DF,DTS,DFW

Variable

Percent canopy closureof trees that producehard mast (e.g., oak,hickory, walnut, pecan,beech) ~ 25.4 cm(10 inches) dbh.

><OJ

"'0.= 0.8

~.... 0.6.........0

~0.4....::::l

V) 0.2

25 50

%

75 100

DF, DTS ,DFW Distance to availablegrain.

6

1. 0 -t---.+-...........-..---L-..........+

><OJ-g 0.8

.....

~0.6..............010 0.4~....::::lV) 0.2

200 400 600 800 (m)220 440 660 880 (yd)

DF,DTS,DFW

DF,DTS,DFW

Average dbh ofoverstory trees.

Percent tree canopyclosure.

1.0XQJ

-g 0.8......

~.,.. 0.6,....,...0s 0.4.,..:::s(/) 0.2

1.0XQJ

-g 0.8......

~0.6.,..,....,...0~ 0.4

12.5 25.0 37.5 50.8 (em)5 10 15 20 (in)

25 50

%

75 100

DF,DTS,DFW

Percent shrub crowncover.

1.0

~-g 0.8......

~0.6.,..,....,...0ltl 0.4~.,..:::s(/)0.2

7

25 50%

75 100

Equations. In order to obtain life requisite values for the fox squirrel,the SI values for appropriate variables must be combined with the use ofequations. A discussion and explanation of the assumed relationships betweenvariables was included under Model Description. The suggested equations forobtaining the food and cover/reproduction values are presented in Figure 2.

Li fe requi sHe

Winter food

Cover/reproduction

Cover type

DF ,DTS ,DFW

DF ,DTS ,DFW

Equations

Figure 2. Equations for determining life requisite valuesby cover type for the fox squirrel.

HSI determination. A HSI value for a single cover type species is basedon the limiting factor concept and equals the lowest life requisite value.

Application of the Model

Definitions of variables and suggested field measurement techniques (Hayset al. 1981) are presented in Figure 3.

Variable [definition]

Percent canopy closureof trees that producehard mast (e.g., oak,hickory, walnut, pecan,beech) ~ 25.4 cm (10 inches)dbh [the percent of theground that is shadedby the vertical projec-tion of the canopies oftrees which produce ahard shelled fruit andhave a dbh of at least25.4 cm (10 inches)].

Cover types

DF ,DTS ,DFW

Suggested technique

Calculated area ofplant using crowndiameter on stripquadrat

Figure 3. Definitions of variables and suggested measurement techniques.

8

Variable [definition}

Distance to available grain[the linear distance fromsample point to grain cropsthat are available to foxsquirrels. Grain may beavailable as standing crop,waste, or stored grain].

Average dbh of overstorytrees [the averagediameter at breast height(1.4 m/4.5 ft) of thosetrees which are ~ 80percent of the heightof the tallest treein the stand.

Percent tree canopyclosure [the percentof the ground surfaceshaded by a verticalprojection of thecanopies of all woodyvegetation greaterthan 5.0 m (16.5 ft)ta11].

Percent shrub crowncover [the percent ofthe ground shaded bya vertical projec-tion of the canopiesof woody vegetationless than 5 m (16.5 ft)ta11] .

Cover types

DF,DTS,DFW

DF ,DTS ,DFW

DF,DTS,DFW

DF,DTS,DFW

Suggested technigue

On site inspection,remote sensing

Cruise for tallest treein stand. Sample withoptical range finderand Biltmore stick onstrip quadrat

Li ne intercept,remote sensing

Li ne intercept

Figure 3. (concluded)

SOURCES OF OTHER MODELS

Numerical habitat models by Flood et al. (1977) and Hallett (1980) werelocated in the literature.

REFERENCES

Adams, C. E. 1976. Measurements and characteristics of fox squirrel, Sciurusniger rufiventer, home ranges. Am. Midl. Nat. 95(1):211-215.

9

Allen, D. L. 1943. Michigan fox squirrel management. Michigan Dept. ofConserv., Game Div. Publ. 100. 404 pp.

Armstrong, D. M. 1972. Distribution of mammals in Colorado. University ofKansas. Lawrence, Kansas. 415 pp.

Bailey, R. G. 1980. Description of the ecoregions of the United States.U.S.D.A. For. Servo Misc. Publ. 1391. 77 pp.

Baker, R. H. 1944. An ecological study of tree squirrels in eastern Texas.J. Mammal. 25(1):8-24.

Bakken, A. 1952. Interre1atonships of Sciurus carolinensis (Gmelin) andSciurus niger (Linneaus) in mixed populations. Ph.D. Thesis., Univ.Wisc., . 188pp. Cited by Taylor 1974.

Barkalow, F. S., Jr. Personal communication. Zoology Dept., North Car~lina

State Univ., Raleigh.

Baumgartner, L. L. 1939. Fox squirrel dens. J. Mammal. 20(4):456-465.

1943. Fox squirrels in Ohio. J. Wi1d1. Manage. 7(2):193-202.

Brown, L. G., and L. E. Yeager. 1945. Fox and gray squirrels in Illinois.Illinois Nat. Hist. Surv. Bull. 23(5):449-532.

Donohoe, R. W., and R. O. Beal. 1972. Squirrel behavior determined by radiotelemetry. Ohio Dept. Nat. Resour., Fish and Wildl. Rep. 2. 20 pp.

Flood, B. S., M. E. Sangster, R. D. Sparrowe, and T. S. Baskett. 1977. Ahandbook for habitat evaluation procedures. U.S.D.I. Fish Wildl. ServoRes. Publ. 132. Washington, D.C. 77 pp.

Goodrum, P. 1938. Squirrel management in eastern Texas. Trans. N. Am.Wildl. Conf. 3:670-676.

Hays, R. L., C. Summers, and W. Seitz. 1981. Estimating wildlife habitatvariables. U.S.D.I. Fish and Wildl. Servo FWS/OBS-81/77. 111 pp.

Hallett, D. L. 1980. Fox squirrel (Sciurus niger). Pages 42-48 i!! T. S.Baskett, D. A. Darrow, O. L. Hallett, M. J. Armbruster, J. A. Ellis, B.F. Sparrowe, and P. A. Koste, eds. A handbook for terrestrial habitatevaluation in central Missouri. U.S.D.l. Fish and Wildl. Servo Res.Publ. 133. Washington, D. C. 155 pp.

Korschgen, L. J. 1981. Foods of fox and gray squi rre1sin Mi ssouri. J.Wi1d1. Manage. 45(1):260-266.

Lowery, G. H., Jr. 1974. The mammals of Louisiana and its adjacent waters.Louisiana State Univ. Press, Baton Rouge. 565 pp.

10

MacClintock, D. 1970. Squirrels of North America. Van Nostrand ReinholdCo., New York. 184 pp.

McConnell, C. A. Personal communication (letter dated 21 November 1978),Wildlife Management Institute, Washington, D.C.

Nixon, C. M. Personal communication (letter dated 2 October 1981). IllinoisInst. Nat. Resour., Champaign, Ill.

Nixon, C. M., S. P. Havera, and L. P. Hansen. 1980. Initial response ofsquirrels to forest changes associated with selection cutting. Wildl.Soc. Bull. 8(4):298-306.

Sanderson, H. R., C. M. Nixon, R. W. Donohoe, and L. P. Hansen. 1980. Grape­vines - an important component of gray and fox squirrel habitat. Wildl.Soc. Bull. 8(4):307-310.

Taylor, G. J. 1974. Present status and habitat survey of the Delmarva foxsquirrel (Sciurus niger cinereus) with a discussion of reasons for itsdecline. Proc. Southeastern Assoc. Game and Fish Commissioners27:278-289.

u.S. Fish and Wildlife Service. 1981. Standards for the development ofhabitat suitability index models. 103 ESM. U.S.D.l. Fish Wildl. Serv.,Div. Ecol. Servo n.p.

U.S. Forest Service. 1971. Wildlife habitat management handbook. SouthernRegion. U.S.D.A. For. Servo FSH 2609.23. n.p.

Wright, G. M. 1979. Range extension of the fox squirrel in southeasternWashingtqn and into adjacent Idaho. Murrelet 60(2):73-75.

11

,I 3. Recipient's ACCHsion No.

I!5. RePOrt Dete

! July 1982

I~REPORT DOCUMENTATION 11. REPORT NO.

PAGE " - FWS/OBS-82/10. 18

7. ",uthor(s)Arthur W. A11 en

4. Title and SubtItle

50272 -, 01

Habitat Suitability Index Models: Fox Squirrel I~

1---------------------.------------ tl-------------1

11. Contnet(C) or Grsnt(G) No.

I (e)

I(a,I

113. Type of Report & Perlod Covered

I

Hab ita t Eva1uati on Procedures Group' 10. Praiec:t/T.sk/Worll Unit No.

Western Energy and Land Use TeamU.S. Fish and Wildlife ServiceDrake Creekside Building One2625 Redwing RoadFort Collins, Colorado 80526Western Energy and Land Use TeamOffice of Biological ServicesFish and Wildlife ServiceU.S. Department of the InteriorW~~h;nntnn nr. ?O?L1.0

1~ Spansorin. 0rKanizatlon Neme and Add.....

9. Performin. OrKenization Neme end Add,..••

15. Supplementary Notes

1~ Abstract (Limit: 200 words)

Habitat preferences and species characteristics of the fox squirrel (Sciurus niger)are described in this publication. It is one of a series of Habitat SuitabilityIndex (HSI) models and was developed through an analysis of available scientificdata on the species-habitat requirements of the fox squirrel. Habitat use infor- 41mation is presented in a review of the literature, followed by the development of ~

a HSI model. The model is presented in three formats: graphic, word, and mathe­matical. Suitability index graphs quantify the species-habitat relationship. Thesedata are then synthesized into a model which is designed to provide information foruse in impact assessment and habitat management activities.

17. Document An.lysis a. Deserlpto~

WildlifeAnimal behaviorAnimal ecologyHabi tabi 1i tyMathematical modelsb. Identifiers/Open·Ended Terms

Fox squi rrelSciurus nigerHabitat suitabilityHabitat preference

MammalsSquirrels

Habitat managementHabitat suitability index modelsHabitat requirementsSpecies-habitat relationships

Impact assessment

c. COSATI Field/Group

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I ', SotIMI ... "" 'IUM .•• ·• •

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