Variable (definition

Number of snags 225 cm dbh
per ha [actual or estimated
number of standing dead

trees 225 cm dbh and 21.8 m
tall. Trees in which 250%

of the branches have fallen,
or are present but no longer

bear foliage, are to be
considered snags].

Mean dbh of overstory
trees [the mean diam-
eter at breast height
(1.4 m) above the ground
of those trees that are
280% of the height of
the tallest tree in the
stand].

Percent canopy cover of
trees [the percent of the
ground surface that is
shaded by a vertical pro-
jection of all woody
vegetation >6.0 m tall].

Percent overstory pine
canopy closure [the
percent of the ground
surface that is shaded by
a vertical projection of
all pines (Pinus spp.)
>6.0 m tall and 280% of
the height of the tallest
tree in the stand; re-
commended for use in
eastern U.S. forests only

(see text for explanation)].

Cover types

OF, EF ,DFW,
EFW

OF,EF,DFW,
EFW

OF ,EF,DFW,
EFW

OF EF DFW,
EFW

Suggested technique

Quadrat, remote sensing

Diameter tape

Line intercept, remote
sensing

Line intercept, remote
sensing

Figure 4. Definitions of variables and suggested measuring techniques.

13


Dr. F.J. Alsop, III, East Tennessee State University, Johnson City
Dr. C.E. Bock, University of Colorado, Boulder

Dr. R.N. Conner, U.S. Forest Service, Nacogdoches, TX

Dr. J.A. Jackson, Box Z, Mississippi State, MS

Dr. F.C. James, Florida State University, Tallahassee

Dr. B.J. Schardien Jackson, Mississippi State, MS

Initial results indicated that outputs from the earlier model were poorly
correlated (r=0.07, P>0.50) with habitat ratings by experts for 40 sites in
eastern Tennessee (O'Neil et al. 1988). Important habitat criteria identified
by the experts were used to modify the model in an attempt to more closely
mimic the procedures used by experts to rate habitats. The major changes to
the model as a result of the field evaluation were (1) optimum suitability for
the average diameter of overstory trees was changed from 25 to 38 cm; (2) snags
were assigned greater importance than live trees for nesting; (3) the variable
"bercent canopy cover of pines" was added to reflect a strong negative correla-
tion (r=-0.91, P<0.001) between this variable and habitat ratings by species
authorities; (4) the mathematical function used to calculate the cover
suitability index was changed from a geometric mean to a multiplicative
function; and (5) the suitability relationship for tree canopy closure was
changed from a preference for moderate canopy closure to a preference for
dense forest canopy. Correlation of outputs from the modified model to habitat
ratings by species authorities improved considerably (r=0.82, P<0.001) (O'Neil
et al. 1988).

All of the changes to the model as a result of the field evaluation were
based on input from species experts and reflect hairy woodpecker ecology in
forests in the eastern United States. The variable “percent canopy cover of
pines" is not recommended as an appropriate variable in western forests; use
of the model in western vs. eastern forests is described below. The current
model is the direct result of the field evaluation; it has not been field
tested.

Model Description

Overview. The hairy woodpecker can satisfy all of its habitat require-
ments within any one of the forested cover types listed above. Reproductive
and cover needs are evaluated in this model. Although sufficient food is an
obvious life requisite of the hairy woodpecker, I assume in this model that
food will never be more limiting than cover and reproductive requirements and
that water is not a limiting factor.

The following sections identify important habitat variables, describe
suitability levels of the variables, and describe the relationships between
variables.


Graber, J.W., R.R. Graber, and E.L. Kirk. 1977. Illinois birds: Picidae.
Illinois Nat. Hist. Surv. Biol. Notes 102. 73 pp.

Haapanen, A. 1965. Bird fauna of the Finnish forests in relation to forest
succession. I. Ann. Zool. Fenn. 2:154-196. [Cited by Smith (1980).]

Hardin, K.I., and K.E. Evans. 1977. Cavity nesting bird habitat in the
oak-hickory forest ... a review. U.S. For. Serv. Gen. Tech. Rep. NC-30.
23 pp.

Hays, R.L., C. Summers, and W. Seitz. 1981. Estimating wildlife habitat
variables. U.S. Fish Wild]. Serv. FWS/OBS-81/47. 111 pp.

Jackman, $.M. 1975. Woodpeckers of the Pacific Northwest: their character-
istics and their role in the forests. M.S. Thesis. Oregon State University,
Corvallis. 147 pp.

Kilham, L. 1968. Reproductive behavior of hairy woodpeckers. II. Nesting
and habitat. Wilson Bull. 80(3):286-305.

Kisiel, D.S. 1972. Foraging behavior of Dendrocopus villosus and 0. pubescens
in eastern New York state. Condor 74(4):393-398.

Koplin, J.R. 1967. Predatory and energetic relations of woodpeckers to the
Engelmann spruce beetle. Ph.D. Dissertation. Colorado State University,
Ft. Collins, 187 pp.

Kroll, J.C., and R.R. Fleet. 1979. Impact of woodpecker predation on over-
wintering within-tree populations of the Southern pine beetle (Dendroctonus
frontalis). Pages 269-281 in J.G. Dickson, R.N. Conner, R.R. Fleet, J.C.
Kroll, and J.A. Jackson, eds. The role of insectivorous birds in forest
ecosystems. Academic Press, New York.

Larrison, E.J., and K.G. Sonnenberg. 1968. Washington birds: their location
and identification. Seattle Audubon Society, Seattle. 258 pp.

Lawrence, L. Dek. 1966. A comparative life-history study of four species of
woodpeckers. Ornithol. Monogr. No. 5, American Ornithologists’ Union.
156 pp.

Mannan, R.W. 1977. Use of snags by birds, Douglas-fir region, western Oregon.
M.S. Thesis. Oregon State University, Corvallis. 114 pp.

Mannan, R.W., E.C. Meslow, and H.M. Wight. 1980. Use of snags by birds in
Douglas-fir forests, western Oregon. J. Wildl. Manage. 44(4) : 787-797.

Massey, C.L., and N.D. Wygant. 1973. Woodpeckers: most important predators
of the spruce beetle. Colorado Field Ornithol. 16:4-8.

17




Model assumptions. A number of assumptions were made in the development
of this HSI model.

1.

The criteria identified for evaluation of hairy woodpecker habitat
are generally assumed to be appropriate throughout the range of the
species. Many of the variables and variable relationships identified
in the model resulted from a field test of an earlier HSI model in
eastern Tennessee. As a result, the model is probably best suited
for application in the southeastern United States. No information
is available to indicate the model's applicability to other parts of
the United States, except there is adequate information that the
presumed negative influence of pines does not apply to western U.S.
forests (see number 7 below).

Nest sites can be provided by a combination of snags and live trees,
but live trees in the absence of snags cannot provide optimal nesting
habitat.

A measure of the average diameter at breast height of overstory
trees is assumed to be an adequate estimator of the suitability of
live trees for nesting. An adequate number of trees in suitable
condition (i.e., with decayed heartwood) is assumed to be present as
long as the cover type is classified as a forest (i.e., has >25%
canopy cover) and tree diameter is suitable.

All tree species are assumed to be available for excavation by hairy
woodpeckers. It is possible that some: species may not typically
have decayed heartwood and, therefore, will be unsuitable for
excavation. It is also possible that some tree species will be
unsuitable for excavation because of resins or the density of the
wood. Little definitive evidence is available, however, to determine
whether some tree species are absolutely unsuitable for excavation
by hairy woodpeckers.

Hairy woodpeckers can inhabit a variety of forested habitats, but
potential nesting in live trees will only be provided by older
forest stands with large trees.

Hairy woodpeckers prefer forest stands with a dense canopy. This
assumption may be valid in the southeastern United States but may be
invalid in the western United States, where the forest canopy is
generally less dense than in the east. The relationships described
for percent canopy cover of trees and habitat suitability (Figure 2b)
may need to be redefined for use in western forest habitat if the
standard of comparison in such applications is intended to be the
best regional habitat. Use of the model without modification will
yield outputs based on a standard of comparison developed in the
southeastern United States.

14


$0272-101

REPORT DOCUMENTATION
PAGE

1, REPORT NO. 2

Biological Report 82(10.146)

3. Recipient's Accession No.

‘4 Title and Subtitie

Habitat Suitability Index Models: Hairy Woodpecker

5. Report Date

September 1987

6

@

7. Author(s)
P. J. Sousa

8. Performing Organization Rept. No.

% Performing Organization Name ang Address National Ecology Research Center

U.S. Fish and Wildlife Service
Drake Creekside One Bldg.

2627 Redwing Rd.

Fort Collins, CO 80526-2899

10. Project/Task/Work Unit No.

11, Contract(C) or Grant(G) No.
©

s)

12. Sponsoring Organization Name and Address National Ecology Research Center
Research and Development
Fish and Wildlife Service
Department of the Interior
Washington, DC 20240

13. Type of Report & Period Covered

14.

15. Supplementary Notes

16. Abstract (Limit: 200 words)

habitat).

Previously developed by the U.S. Fish and Wildlife Service,

A review and synthesis of existing information were used to develop a Habitat
Suitability Index (HSI) model for the hairy woodpecker (Picoides villosus).
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

HSI models are designed to be used with Habitat Evaluation Procedures

The model

e

17. Document Analysis a. Descriptors

Birds
Wildlife
Habitability
Mathematical models
b. Identifiers/Open-Ended Terms
Hairy woodpecker
Picoides villosus
Habitat suitability

¢ COSATI Fleld/Group

1. Availability Statement 19. Security Class (This Report) 21. No. of Pages
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Bull, E.L. 1978. Specialized habitat requirements of birds: snag management,
old growth, and riparian habitat. Pages 74-82 in R.M. DeGraaf, tech. coord.
Proceedings of the workshop on nongame bird habitat management in the
coniferous forests of the western United States. U.S. For. Serv. Gen. Tech.
Rep. PNW-64.

Calef, R.T. 1953. Ecological analysis of the flora and vertebrate fauna of
Funks Forest National Area, McClean Co., I1]. M.S. Thesis. University of
Illinois. 85 pp. [Cited by Graber et al. (1977).]

Conner, R.N. 1980. Foraging habitats of woodpeckers in southwestern Virginia.
J. Field Ornith. 51(2):119-127.

Conner, R.N., and C.S. Adkisson. 1976. Discriminant function analysis: a
possible aid in determining the impact of forest management on woodpecker
nesting habitat. Forest Sci. 22(2):122-127.

Conner, R.N., and C.S. Adkisson. 1977. Principal component analysis of
woodpecker nesting habitat. Wilson Bull. 89(1):122-129.

Conner, R.N., and H.S. Crawford. 1974. Woodpecker foraging in Appalachian
clearcuts. J. For. 72:564-566.

Conner, R.N., R.G. Hooper, H.S. Crawford, and H.S. Mosby. 1975. Woodpecker
nesting habitat in cut and uncut woodlands in Virginia. J. Wildl. Manage.
39(1):144-150.

Conner, R.N., O.K. Miller, Jr., and C.S. Adkisson. 1976. Woodpecker
dependence on trees infected by fungal heart rots. Wilson Bull.
88(4) :575-581.

Diem, K.L., and S.I. Zeveloff. 1980. Ponderosa pine bird communities.
Pages 170-197 in R.M. DeGraaf and N.G. Tilghman, compilers. Management of
western forests and grasslands for nongame birds. U.S. For. Serv. Gen.
Tech. Rep. INT-86.

Evans, K.E., and R.N. Conner. 1979. Snag management. Pages 214-225 in
R.M. DeGraaf and K.E. Evans, compilers. Management of northcentral and
northeastern forests for nongame birds. U.S. For. Serv. Gen. Tech. Rep.
NC-51.

Fitch, H.S. 1958. Home ranges, territories, and seasonal movements of
vertebrates of the Natural History Reservation. Univ. Kansas Publ. Mus.
Nat. Hist. 11(3):63-326.

Galli, A.E., C.F. Leck, and T.T. Forman. 1976. Avian distribution patterns
in forest islands of different sizes in central New Jersey. Auk
93(2) :356-364.

Gamboa, G.J., and K.M. Brown. 1976. Comparative foraging behavior of six
sympatric woodpecker species. Proc. Iowa Acad. Sci. 82:179-181.

16


Suitability Index (SIV3)

1.0 L 1 : = 1.0 1 1 \
=
0.8 4 L 2 0.84 7
x
ov
0.6 4 L = 0.64 L
0.44 L Pod L
0.24 L 8 0.24 L
8
0.0 7 , : 0.0 Renn r
0 10 20 30 40+ (cm) 0 2 50 75 100

0 4 8 12 16+ (inches)
Mean dbh of overstory trees

Percent canopy cover of trees

c

—~ 1.0 coe

wo

=

2 0.8 4 b
<

o

So. 4 L
Poa L
8 0.2 4 .
5

? 0.0 T — T

0 25 50 75 100

Percent overstory pine
canopy closure

Figure 2. Relationships between variables used to evaluate cover for the
hairy woodpecker and suitability levels for the variables.

ll


are relatively soft-wooded trees (compared to oaks) that can be easily
excavated by some species of woodpeckers. He suggests that the lack of use
may be due to the absence of heartwood decay or to resin produced by spruce
rather than to the density of the spruce wood. Whatever the reason for the
observed lack of use, Conner believes that insufficient data exist to
categorically classify live spruces as unsuitable for excavation by hairy
woodpeckers.

Preferred nesting areas of hairy woodpeckers in east Tennessee were
characterized by a large number of trees >23 cm dbh and associated high canopy
biomass (Anderson and Shugart 1974). Hairy woodpeckers in Virginia apparently
preferred areas with high stem density, but nested in areas with a wide range
of basal areas, canopy heights, stem densities, and distances from cleared
areas (Conner and Adkisson 1977). In northwestern Washington, hairy woodpecker
nests were found in a variety of successional stages, though most were in, or
at the edge of, old-growth forests (Zarnowitz and Manuwal 1985). Hairy wood-
peckers in Washington are found in open rather than dense stands of timber
(Larrison and Sonnenberg 1968), and in California's Sierra Nevada they prefer
forests of low to moderate canopy closure (</0%) (Verner 1980). Both under-
stocked and fully stocked stands in Virginia were suitable nesting areas as
long as decayed trees were present (Conner et al. 1975). Hairy woodpeckers
have even been reported nesting in the grass-forb stage of mixed coniferous
forest regeneration by using stumps <1.5 m tall (Verner 1980).

Hairy woodpeckers require trees with a minimum dbh of 25 cm and a minimum
height of 4.6 m for nesting (Thomas et al. 1979). Raphael and White (1984:24)
found that "...diameter was the tree characteristic most closely correlated
with nesting use" for 17 cavity-nesting birds. Conner and Adkisson (1976)
found that canopy height had a greater influence on distinguishing between
"possible nesting habitat" and "not nesting habitat" than did either basal
area or stem density. In Vermont, no significant difference in mean tree
height was detected between nest trees and adjacent non-nest trees (Runde and
Capen 1987). Diameter at breast height (dbh) and diameter at nest height
(dnh) were significantly greater for nest trees than mon-nest trees
(® dbh:27.141.3 cm vs. 23.940.7 cm, P<0.05; X dnh:22.441.1 cm vs. 13.249.6 cm,
P<0.01). The probable optimum diameter range for hairy woodpecker nest trees
is 25 to 35 cm dbh, and the probable optimum height range for nest trees is 6
to 12m (Evans and Conner 1979). In Douglas-fir forests, however, hairy
woodpeckers nest in older second-growth (41 to 120 yr) and mature (120+ yr)
forests (Meslow and Wight 1975); these age classes are presumably taller than
the optimum range suggested by Evans and Conner (1979). The average height of
eight trees used for nesting in a Colorado aspen forest was 18 m, and ranged
from about 11 to 21.3 m (Scott et al. 1980). Ten trees used for nesting in
Virginia averaged 13.0 m tall and ranged from 4 to 26.5 m (Conner et al.
1975). The diameter of the tree at the cavity level in these 10 trees averaged
25.2 cm and ranged from 20 to 46 cm. In California, 19 nest trees averaged
13.7 m tall with an average diameter at the cavity level of 36.342.09 cm
(Raphael and White 1984). Table 1 summarizes tree condition, nest heights,
and nest tree diameter from several studies.


ACKNOWLEDGMENTS

A field validation of an earlier version of the HSI model for the hairy
woodpecker was conducted under the direction of Ms. L. Jean O'Neil, U.S. Army
Corps of Engineers, Waterways Experiment Station, Vicksburg, MS. The field
validation was based on habitat evaluation by the following individuals:

Dr. F.J. Alsop, III, East Tennessee State University, Johnson City

Dr. C.E. Bock, University of Colorado, Boulder

Dr. R.N. Conner, U.S. Forest Service, Nacogdoches, TX

Dr. J.A. Jackson, Box Z, Mississippi State, MS

Dr. F.C. James, Florida State University, Tallahassee

Dr. B.J. Schardien Jackson, Mississippi State, MS

Mr. J. Teaford and Dr. T. Roberts, Waterways Experiment Station, and
Dr. J. Wakeley, Pennsylvania State University, assisted in the study design,
data collection, data analysis, and model modification. The field validation
resulted in several improvements in the model. The efforts of all of those
involved in the field validation are very much appreciated.

Earlier drafts of the model were reviewed by Dr. R.N. Conner and Dr. C.E.
Bock. Their review comments led to significant improvements in the model and
are appreciated.

Word processing of this document was provided by C. Guizow, D. Ibarra,
P. Gillis, and E. Barstow. The cover was illustrated by J. Shoemaker.

vi


CONTENTS

PREFACE ........
ACKNOWLEDGMENTS

HABITAT USE INFORMATION 20... 0... ccc cece eee eee cee eee e teenie eene
General ...........0.0.
Food ....
Water
Cover
Reproduction ..............4..
Interspersion and Composition
Special Considerations .............
HABITAT SUITABILITY INDEX (HSI) MODEL
Model Applicability .............00.
Model Description .......
Application of the Model .
SOURCES OF OTHER MODELS ........... cece cece cece cence eee e nee

REFERENCES 20... cece ec cece cece cent e eee n eee e tenet eens 15


HSI determination. The suitability index for the cover component is
assumed to directly modify the suitability index for the reproduction component ¢
(Equation 3) to yield an overall HSI value for the hairy woodpecker in the
habitat being evaluated. At optimal cover component conditions (i.e.,
SIC=1.0), the reproduction component will determine the habitat suitability

index. If cover conditions are anything less than optimum, then the
reproduction value will be reduced based on the quality of the cover
conditions.

HSI = SIN x SIC, or
HSI = [SIV1 + (0.75 x SIV2)] x (SIV3 x SIV4 x SIV5) (3)

[Note: In instances where SIN >1.0, it should be set equal to 1.0 prior
to using Equation 3.]

Application of the Model

Summary of model variables. Several habitat variables are used in this
model to evaluate habitat suitability for the hairy woodpecker. The relation~
ships between habitat variables, life requisites, cover types, and an HSI are
summarized in Figure 3. The definitions and suggested measurement techniques

(Hays et al. 1981) for the variables used in this model are listed in Figure 4. C
Habitat variable Life requisite Cover types
Number of snags
225 cm dbh/ha
Reproduction—

Mean dbh of Deciduous Forest
overstory trees Evergreen Forest

Deciduous Forest-

ed Wetland HST
Mean dbh of ——————— Evergreen Forest-
overstory trees ed Wetland
Percent canopy cover —
of trees Cover

Percent overstory pine—
canopy closure

Figure 3. Relationships of habitat variables, life requisites, and cover types
to the HSI for the hairy woodpecker.

e

12


Hairy woodpeckers in southwestern Virginia foraged in"... habitats with
relatively dense vegetation near the ground" (Conner 1980:121) in comparison
to foraging habitat selected by other species of woodpeckers, especially the
downy woodpecker (P. pubescens).

Water

No specific information on water requirements of the hairy woodpecker was
found in the literature.

Cover

Hairy woodpeckers inhabit a wide variety of forest cover types. For
example, they inhabit Douglas-fir forests (Mannan et al. 1980), ponderosa pine
forests (Diem and Zeveloff 1980), pinyon-juniper (Pinus edulis - Juniperus
spp.) woodlands (Balda and Masters 1980), eastern deciduous forests (Conner
et al. 1975), and riparian communities (Stauffer and Best 1980). Winter
population densities of hairy woodpeckers in Illinois were positively cor-
related with the number of trees >56 cm dbh and with a diversity of genera and
species of large trees (Graber et al. 1977). Hairy woodpeckers in Oregon use
the shrub/sapling (8 to 15 yr) and second-growth (16 to 40 yr) stages of
Douglas-fir forests, but they do not nest in these younger stages (Meslow and
Wight 1975). Jackman (1975) stated that hairy woodpeckers inhabit second-
growth, partially thinned, and other altered forest types; however, hairy
woodpeckers were reported more frequently (95% of 40 breeding bird censuses)
in mature undisturbed habitats in the northern hardwoods region than in
disturbed and successional habitats (43% of 30 censuses) (Noon et al. 1979).

Hairy woodpeckers use tree cavities for roosting and winter cover, as
well as for nesting and rearing young (Thomas et al. 1979), and they will
excavate new cavities in the fall to be used for roosting (Jackman 1975).

Reproduction

The hairy woodpecker is a primary cavity nester that is able to adapt to
a wide variety of habitats (Kilham 1968). In the Pacific Northwest, hairy
woodpeckers require standing dead trees and live trees with rotted heartwood
(Jackman 1975). Similarly, hairy woodpeckers in Virginia exhibited a definite
preference for trees with heartrot (Conner et al. 1975; Conner et al. 1976).
Thomas et al. (1979), however, listed the hairy woodpecker as a species that
usually excavates in sound wood. Runde and Capen (1987) found that the amount
of sound wood varied widely (based on a visual estimate) in live trees used
for nesting by hairy woodpeckers; 11 of 21 nests were in live trees. A
possible exception to the apparently general use of live or dead trees for
nest sites is that hairy woodpeckers do not nest in Engelmann spruce (Picea
engelmannii) forests in the Pacific Northwest (Jackman 1975). Haapanen (1965
cited by Smith 1980:264) found that “of all the woodpeckers found in spruce-fir
forests, apparently only the Northern 3-toed Woodpecker [Picoides tridactylus]
is capable of making holes in the dense wood of living spruce trees."
R.N. Conner (U.S. Forest Service, Nacogdoches, TX; letter dated February 19,
1986) suggests, however, that Engelmann spruce and other North American spruces



Meslow, E.C., and H.M. Wight. 1975. Avifauna and succession in Douglas-fir
forests of the Pacific Northwest. Pages 266-271 in D.R. Smith, tech. coord.
Management of forest and range habitats for nongame birds. U.S. For. Serv.
Gen. Tech. Rep. WO-1.

Noon, B.R., V.P. Bingham, and J.P. Noon. 1979. The effects of changes in
habitat on northern hardwood forest bird communities. Pages 33-48 in R.M.
DeGraaf and K.E. Evans, compilers. Management of northcentral and north-
eastern forests for nongame birds. U.S. For. Serv. Gen. Tech. Rep. NC~51.

O'Neil, L.J., T.H. Roberts, J.S. Wakeley, and J.W. Teaford. 1988. A procedure
to modify Habitat Suitability Index models. Wildl. Soc. Bull. 16(4):In
press.

Raphael, M.G., and M. White. 1984. Use of snags by cavity-nesting birds in
the Sierra Nevada. Wildl. Ménogr. 86. 66 pp.

Robbins, C.S. 1979. Effects of forest fragmentation on bird populations.
Pages 199-212 in R.M. DeGraaf and K.E. Evans, compilers. Management of
northcentral and northeastern forests for nongame birds. U.S. For. Serv.
Gen. Tech. Rep. NC-51.

Runde, D.E., and D.E. Capen. 1987. Characteristics of northern hardwood
trees used by cavity-nesting birds. J. Wild]. Manage. 51(1):217-223.

Scott, V.E., J.A. Whelan, and P.L. Svoboda. 1980. Cavity-nesting birds and
forest management. Pages 311-324 in R.M. OeGraaf and N.G. Tilghman,
compilers. Management of western forests and grasslands for nongame birds.
U.S. For. Serv. Gen. Tech. Rep. INT-86.

Smith, K.G. 1980. Nongame birds of the Rocky Mountain spruce-fir forests and
their management. Pages 258-279 in R.M. DeGraaf and N.G. Tilghman,
compilers. Management of western forests and grasslands for nongame birds.
U.S. For. Serv. Gen. Tech. Rep. INT-86.

Stallcup, P.L. 1966. Spatio-temporal relationships of nuthatches and wood-
peckers in northern Colorado. Ph.D. Dissertation. Colorado State
University, Ft. Collins. 111 pp.

Stauffer, D.F., and L.B. Best. 1980. Habitat selection by birds of riparian
communities: evaluating effects of habitat alterations. J. Wildl. Manage.
44(1):1-15.

Thomas, J.W., R.G. Anderson, C. Maser, and €.L. Bull. 1979. Snags.
Pages 60-77 in J.W. Thomas, tech. ed. Wildlife habitats in managed forests:
the Blue Mountains of Oregon and Washington. U.S. For. Serv. Agric.
Handb. 553.

U.S. Fish and Wildlife Service. 1981. Standards for the development of

Habitat Suitability Index models. 103 ESM. U.S. Fish Wildl. Serv., Div.
Ecol. Serv. n.p.

18


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SEPTEMBER 1987 National Wetlands Research Center

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Ae

HABITAT SUITABILITY INDEX MODELS:
HAIRY WOODPECKER

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

yA


Hairy woodpeckers will excavate in both hard and soft snags (Evans and
Conner 1979); however, hairy woodpecker breeding densities were significantly
positively correlated (Ps0.01) with soft snags in Iowa riparian forests
(Stauffer and Best 1980). The hairy woodpecker was categorized as a soft snag
excavator in Sierra Nevada forests (Raphael and White 1984). Evans and Conner
(1979) estimated that 200 snags were necessary in order to support the maximum
population of hairy woodpeckers on 40 ha of forest. Their estimate was based
on a minimum annual need of four cavities per pair, and an assumption that
only 10% of the available snags would be suitable for use. Snag density
requirements decreased in direct proportion to the percentage of maximum
population desired; e.g., 160 snags are required to support 80% of the maximum
population, and 100 snags would support 50% of the maximum population. A
similar estimate for the Blue Mountains of Oregon and Washington was that
180 snags/40 ha are necessary to support maximum populations of hairy wood-
peckers (Thomas et al. 1979). Raphael and White (1984) distinguished between
hard and soft snags in estimating the density of snags required to support the
maximum density of hairy woodpeckers. They assumed a maximum density of
16 pairs/40 ha, an annual rate of excavation of 4 cavities/pair, and a reserve
of 3 suitable cavities per pair to arrive at an estimate of 192 suitable
snags/40 ha to support the maximum density. They further estimated that
4 hard snags are required to produce 1 soft snag, resulting in an estimate of
768 “hard snag equivalents" (Raphael and White 1984:56) per 40 ha. Although
low numbers of snags can, in theory, support low-density woodpecker popula-
tions, enough snags to support 40% of the maximum population was assumed to be
the minimum that will support a self-sustaining population of hairy woodpeckers
in the Pacific Northwest (Bull 1978).

Interspersion and Composition

Territory size in a mature bottomland forest in Illinois averaged 1.1 ha
and ranged from 0.6 to 1.5 ha (Calef 1953 cited by Graber et al. 1977).
Reported territory size of hairy woodpeckers in the Blue Mountains of
Washington and Oregon averaged 2.4 to 3.6 ha (Thomas et al. 1979). Evans and
Conner (1979), however, reported an average territory size of 8 ha based on
available literature, whereas territories reported for two hairy woodpeckers
in Kansas were 9 and 15 ha (Fitch 1958). Home range and territory size are
strongly influenced by habitat quality and, therefore, can be quite variable
(Conner, unpubl.).

In a study of bird use of various sized forested habitats in New Jersey,
hairy woodpeckers did not occur in areas of <2 ha (Galli et al. 1976). A
minimum width of riparian forest necessary to support breeding populations of
hairy woodpeckers in Iowa was 40 m (Stauffer and Best 1980). Robbins (1979)
compared frequency of occurrence of hairy woodpeckers at Breeding Bird Survey
stops in Maryland to the amount of contiguous forested area. The greatest
decrease in frequency of occurrence was recorded at 4 ha of contiguous forested
habitat, and Robbins (1979) proposed this value as a preliminary estimate of
the minimum area necessary to support a viable breeding population of hairy
woodpeckers. Conner (unpubl.), however, believes that 4 ha may represent the
minimal area that hairy woodpeckers will use, but that such a small area could
not support a viable breeding population, which he considers to be a minimum



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HAIRY WOODPECKER (Picoides villosus)

HABITAT USE INFORMATION
General

The hairy woodpecker (Picoides villosus) breeds and winters throughout
most of North America (American Ornithologists' Union 1983). The species is a
primary cavity nester in "deciduous or coniferous forest, well-wooded towns
and parks, and open situations with scattered trees ..." (American
Ornithologists’ Union 1983:391).

Food

Animal matter, such as beetle larvae (Coleoptera), ants (Hymenoptera),
caterpillars (Lepidoptera), and adult beetles, accounted for 78% of the hairy
woodpecker's annual diet, based on 382 stomachs collected throughout North
America (Beal 1911). The diet is supplemented by fruit and mast (Beal 1911;
Hardin and Evans 1977). Hairy woodpeckers forage extensively for seeds in
winter (Jackman 1975); in Colorado, they foraged extensively during the non-
reproductive season on the seeds of ponderosa pine (Pinus ponderosa) (Stallcup
1966). Hairy woodpeckers may concentrate in areas of insect outbreaks in
response to the increased food source (Koplin 1967; Massey and Wygant 1973).
The hairy woodpecker was considered to be a primary predator of the Southern
pine beetle (Dendroctonus frontalis) in east Texas (Kroll and Fleet 1979).

Hairy woodpeckers are considered opportunistic foragers (Raphael and
White 1984); they forage on a variety of substrates, including tree trunks,
stumps, exposed roots (Lawrence 1966), snags, downed logs, the ground (Mannan
et al. 1980), and logging debris in recent clearcuts (Conner and Crawford
1974). In California, hairy woodpeckers foraged on snags 51% of the time and
on live trees 47% of the time (Raphael and White 1984). During winter, hairy
woodpeckers in Virginia foraged most often on dead trees or dead parts of live
trees (Conner 1980). Hairy woodpeckers in New York exhibited a sexual
difference in the selection of winter foraging sites; males foraged on dead
trees significantly more often than females, and females foraged significantly
more often on live trees (Kisiel 1972). Both sexes used a variety of tree
species for foraging sites. A variety of tree species was also used for
foraging by hairy woodpeckers in Sierra Nevada forests (Raphael and White
1984). Snags used for foraging in Douglas-fir (Pseudotsuga menziesii) forests
in Oregon averaged 61 cm dbh and ranged from 13 to 173 cm dbh (Mannan 1977).
The average foraging height of hairy woodpeckers in Iowa was 8.8+1.55 m, and
the average diameter of limbs used for foraging was 6.52+1.04 cm (Gamboa and
Brown 1976). Hairy woodpeckers in New York typically foraged on limbs 5 to
10 cm in diameter (Kisiel 1972).


7. The presence of pines above a minimal level (10%) is considered to
be a negative factor in habitat suitability for the hairy woodpecker
in this model (Figure 2c). Pine and other coniferous forests in the
western United States, however, are regularly used by hairy wood-
peckers. I recommend that this variable be eliminated for
application in western coniferous forests.

8. The hairy woodpecker breeds and winters throughout most of North
America. I assume in this model that the year-round suitability of
a habitat is a function of the habitat suitability during both the
reproductive and nonreproductive seasons. Model users who wish to
evaluate either of the seasons rather than both can simply use the
appropriate portion of this model. Users should be aware that model
outputs in such instances will refer only to a portion of the year-
round needs of the hairy woodpecker.

SOURCES OF OTHER MODELS

Conner and Adkisson (1976) developed a model to distinguish between
"possible nesing habitat" and "not nesting habitat" for the hairy woodpecker
in oak-hickory forests of southwestern Virginia. Three variables were included
in the model: basal area (m?/ha), canopy height to crown cover (m), and stem
density (number/ha). The model includes coefficients for the three variables,
an aggregation function, and a linear decision scale. The model was applied
to two groups, the first consisting of stands containing hairy woodpecker
nests, and the second consisting of six random plots in each of five habitat
types; results of the analysis were significant (P=0.02).

REFERENCES

American Ornithologists’ Union. 1983. Check-list of North American birds.
6th ed. American Ornithologists’ Union. Washington, DC. 877 pp.

Anderson, S.H., and H.H. Shugart, Jr. 1974. Habitat selection of breeding
birds in an east Tennessee deciduous forest. Ecology 55(4) :828-837.

Bailey, A.M., and R.J. Niedrach. 1965. Birds of Colorado. 2 Vols. Denver
Mus. Nat. Hist., Denver, CO. 895 pp.

Balda, R.P., and N. Masters. 1980. Avian communities in the pinyon-juniper
woodland. Pages 146-169 in R.M. DeGraaf and N.G. Tilghman, compilers.
Management of western forests and grasslands for nongame birds. U.S. For.
Serv. Gen. Tech. Rep. INT-86.

Beal, F.E.L. 1911. Food of the woodpeckers of the United States. U.S. Dept.
Agric. Biol. Surv. Bull. 37. 64 pp.

15


PREFACE

This document is part of the Habitat Suitability Index (HSI) model series
[Biological Report 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. 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 informa-
tion 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
reflecting the opinions of identified experts. Habitat information about
wildlife species frequently is represented by scattered data sets collected
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 sugges-
tions 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
U.S. Fish and Wildlife Service

National Ecology Center

2627 Redwing Road

Ft. Collins, CO 80526-2899

iii


Reproduction component. The hairy woodpecker is able to adapt to a
variety of habitats, but suitable reproductive habitats must (1) be dominated ¢

by trees of sufficient size and decay for nesting, (2) have adequate snag
densities, or (3) have some combination of the two.

The number of snags 225.4 cm dbh necessary to support maximum densities
of hairy woodpeckers has been estimated to range from 180/40 ha (Thomas et al.
1979) to 200/40 ha (Evans and Conner 1979), or 4.5 to 5 snags/ha; a snag
density of 5/ha is assumed to represent optimal conditions for reproduction
(Figure la). This estimate refers specifically to nesting and roosting
requirements and may not adequately satisfy foraging needs (Conner, unpubl.).
Potential population density is assumed to decrease proportionally with a
decrease in snag density. Although I assume in this model that low snag
densities will support low woodpecker densities, Bull (1978) assumed that snag
densities <40% of those needed for maximum population density would not support
a self-sustaining population.

g

Suitability Index (SIV1)

1.0 4. 4. rn 1 o 1.0 4. 1 4
=
0.8 4 b 20.8 4 L
3
0.6 4 L 2064 L
0.4 4 L Poa 4 L
0.2 4 L g 0.24 L
3
0.0 ey ? 0.0 ; f r
0 1 2 3 4 5+ (#/ha) 0 10 20 30 40+ (cm)
0 1 2+ (#/acre) ) 4 8 12 16+ (inches)
Number of snags >25cm dbh Mean dbh of overstory trees

Figure 1. Relationships between variables used to evaluate reproductive
habitat for the hairy woodpecker and suitability levels for the variables.


A measure of the seral stage of a forest is the average diameter of the
overstory trees. Hairy woodpeckers may inhabit young forests, but at lower
densities than in older forests. Because they do inhabit forests in a variety
of seral stages, however, this habitat variable should not be strictly
limiting. I assume in this model that the optimal seral stage exists when the
average dbh of overstory trees is >25 cm (Figure 2a). When the average dbh of
overstory trees is <15 cm, suitability is assumed to be one-half of optimum,
j.e., a suitability index of 0.5.

The literature suggests that hairy woodpeckers apparently prefer forests
of moderate canopy cover. Habitat ratings by species experts in the field
test, however, tended to be higher in forest stands with a dense canopy,
except that closed canopy stands were generally rated lower than stands with
<100% canopy cover (O'Neil et al. 1988). I assume that optimal conditions for
this variable occur at 85% to 90% (Figure 2b) with complete canopy cover
representing less than optimal habitat. I further assume that canopy cover
<15% will provide unsuitable habitat conditions. Since the definition of a
forest is a cover type with at least 25% tree canopy cover, any forest wil]
have canopy conditions of some positive suitability level for hairy
woodpeckers.

Hairy woodpeckers inhabit a variety of deciduous, coniferous, and mixed
deciduous-coniferous habitats. Habitat ratings by experts were negatively
correlated (r=-0.91, P<0.001) with the percent canopy closure of pines; sites
completely dominated by pines received relatively low habitat ratings (O'Neil
et al. 1988). I assume in this model that an increase in the canopy cover of
pines in a stand will generally reflect a decrease in habitat suitability for
the hairy woodpecker, although a small amount of pines (<10% canopy cover) is
assumed to contribute to the diversity of cover and prey (Figure 2c). Sites
completely dominated by pines are assumed to have a suitability index for this
variable of 0.2. The apparent influence of pines on hairy woodpecker habitat
suitability described above probably does not apply in western coniferous
forests (C.E. Bock, Environmental, Population and Organismic Biology,
University of Colorado, Boulder; letter dated February 24, 1986). I recommend
that the variable "percent canopy cover of pines" be deleted from the model
for application in western coniferous forests. It is unclear whether a similar
negative relationship exists between other species of conifers in eastern
forests and perceived habitat suitability for the hairy woodpecker.

Results from the field test of the earlier model indicated that the
product of the suitability indices (Equation 2) for the cover component
variables most closely reflected habitat ratings by species experts (O'Neil
et al. 1988).

SIC = SIV3 x SIV4 x SIV5 (2)

As long as an area is classified as a forested type, all of the variables
in Equation 2 will be greater than zero, and the index value for the cover
component will likewise be greater than zero.

10


Suggested citation:

Sousa, P.J. 1987. Habitat suitability index models: hairy woodpecker. U.S.
Fish Wild). Serv. Biol. Rep. 82(10.146). 19 pp.


Verner, J. 1980. Bird communities of mixed-conifer forests of the Sierra
Nevada. Pages 198-223 in R.M. DeGraaf and N.G. Tilghman, compilers.
Management of western forests and grasslands for nongame birds. U.S. For.
Serv. Gen. Tech. Rep. INT-86.

Zarnowitz, J.E., and D.A. Manuwal. 1985. The effects of forest management on

cavity-nesting birds in northwestern Washington. J. Wildl. Manage.
49(1):255-263.

19


Biological Report 82(10.146)
September 1987

HABITAT SUITABILITY INDEX MODELS: HAIRY WOODPECKER

by

Patrick J. Sousa
U.S. Fish and Wildlife Service
National Ecology Center
Creekside One Building
2627 Redwing Road
Fort Collins, CO 80526-2899

U.S. Department of the Interior
Fish and Wildlife Service
Research and Development

Washington, DC 20240


of 250 pairs. He suggested a minimum habitat area of 12 ha to support several
breeding pairs of hairy woodpeckers (R.N° Conner, U.S. Forest Service,
Nacogdoches, TX; letter dated December 1, 1981).

Although the hairy woodpecker is considered a resident species throughout
its range, altitudinal migrations between mountainous areas and lower
elevations do occur (Bailey and Niedrach 1965).

Special Considerations

The hairy woodpecker has been classed as a "tolerant species" to habitat
alteration in Iowa (Stauffer and Best 1980), but also has been suggested as a
sensitive environmental indicator of the ponderosa pine community (Diem and
Zeveloff 1980).

HABITAT SUITABILITY INDEX (HSI) MODEL

Model Applicability

Geographic area. This model was developed for application within forested
habitat throughout the entire range of the hairy woodpecker. Use of the model
differs, however, between forests in the eastern United States and the western
United States. The differences in application are described in the model.

Season. This model was developed to evaluate the year-round habitat of
the hairy woodpecker.

Cover types. This model was developed to evaluate habitat in the follow-
ing forested cover types: Deciduous Forest (DF), Evergreen Forest (EF),
Deciduous Forested Wetland (DFW), and Evergreen Forested Wetland (EFW)
(terminology follows U.S. Fish and Wildlife Service 1981).

Minimum habitat area. A minimum of 4 ha of forested habitat has been
estimated to be necessary to support a viable breeding population of hairy
woodpeckers (Robbins 1979), although Conner (unpubl.) believes that such a
small area may represent the minimum needed to support one pair rather than a
viable breeding population. Conner (unpubl.) suggested 12 ha as a reasonable
estimate of the area needed to support several pairs of hairy woodpeckers.
Additionally, forested riparian zones should be at least 40m wide to be
considered as potential breeding habitat for hairy woodpeckers (Stauffer and
Best 1980).

Verification level. An earlier draft of the HSI model for the hairy
woodpecker was used in a field evaluation of model outputs compared to expert
opinion (O'Neil et al. 1988). The following species experts participated in
the field evaluation:


Hairy woodpeckers can excavate cavities in live trees provided that
heartrot is present, and thus may inhabit a forested area even in the absence
of snags. Runde and Capen (1987) believed that trees >30 cm dbh would be most
useful to hairy woodpeckers, downy woodpeckers, and yellow-bellied sapsuckers
(Syphrapicus varius). For this model, I assume that if the average dbh of
overstory trees is 238 cm, then trees will be of optimum size for nesting. I
assume that an adequate number of available (i.e., with heartrot) live trees
will be present if the average dbh of overstory trees is 238 cm. There is
little evidence correlating tree diameter and presence of heartrot, but the
alternative is to physically examine trees for heartrot; this level of detail
is presumed to be too great for the typical application of this model. Use of
the average dbh of overstory trees does not consider the absolute number of
available live trees. I assume that if an area meets the minimum requirements
to be classified as a forest and is >4 ha, then the total number of trees
available for potential nesting will be optimal. Assuming that adequate
numbers of trees are present, the size and condition of the trees will
determine whether the nesting potential will be low or high. The minimum
reported dbh of a tree used for nesting by hairy woodpeckers is 20.1 cm (Conner
et al. 1975). Thus, I assume that optimal conditions for this variable exist
when the average dbh of overstory trees is 238 cm, and that conditions are
unsuitable when the average dbh of overstory trees is <20 cm (Figure 1b). The
values defining optimum and suitable levels of this variable are based on
results of the field test mentioned earlier.

Overall nesting suitability is a function of the availability of snags or
live trees. In the field test, experts consistently rated habitats without
snags lower than habitats with snags (O'Neil et al. 1988), presumably because
hairy woodpeckers cannot excavate in undecayed trees and prefer to forage on
dead snags (Conner, unpubl.). Habitat suitability ratings in habitats without
snags that were otherwise suitable were generally between 0.7 and 0.8 (on a
0-1 scale). I assume, therefore, that habitats without snags (i.e., all
potential nest sites are in live trees) will have a maximum suitability rating
of 0.75. An overall suitability index for nesting (SIN), based on the
relationships described above, can be determined with Equation 1.

SIN = SIV1 + (0.75 x SIV2) Q)

[Note: If the value resulting from Equation 1 exceeds 1.0, it should be
set to 1.0.]

Cover component. Besides having sufficient potential nest sites, at
least three other habitat factors affect the overall suitability of a habitat
for hairy woodpeckers. These three factors are the seral stage of a forest
stand, the degree of canopy cover of the forest, and the proportion of pines
in the canopy. These variables are assumed to influence food availability,
foraging, nesting suitability, and cover, but are aggregated into a cover
component in this model. Because these factors affect overall habitat
suitability, they will be used in this model as modifiers of the reproductive
value.