BIOLOGICAL DATA AND HABITAT REQUIREMENTS
WILDLIFE SPECIES: Accipiter striatus | Sharp-Shinned Hawk 



TIMING OF MAJOR LIFE HISTORY EVENTS : 
Spring Migration:  In Maryland, spring migration occurs from February 25
to March 5, with peak activity from April 5 to May 5 [48].  In Oregon,
sharp-shinned hawks arrived on nesting grounds in late April, the latest
of the three accipiter species nesting in the area [42].

Nest Building:  In Maryland, nesting activities commence in early May.
Nesting is initiated until mid-July [48].  The sharp-shinned hawk nest
consists of sticks and twigs and is lined with strips of bark.  It is up
to 2 feet (0.6 m) across, usually situated in a crotch or branch of a
tree next to the trunk, and ranges from 10 to 60 feet (3-18 m) above the
ground.  New nests are usually built each year, but sharp-shinned hawks
occasionally adapt a squirrel (Tasaciurus and Sciurus spp.) or crow
(Corvus spp.)  nest [14,50].

Clutch:  Eggs are laid from May to July.  During egg production, eggs
are laid on alternate days [40].  In New York, egg dates range from
April 16 to June 21 [9].  In Wyoming, the earliest egg laying date was
June 16 [7].  In Oregon, mean clutch completion date was May 26 and did
not vary much with elevation [42].  Clutch size is usually four or five
eggs, but ranges from three to eight eggs [14,50].  Eggs are incubated
by both parents [50]; incubation periods range from 34 to 35 days [9],
and all eggs usually hatch within a 36-hour period [40].  There is
usually only one brood per nesting season [9].

Development of Young:  In Wyoming the average number of days in the nest
was 21, with a maximum number of 28 days [7].  Reynolds [42] reported an
average nestling period in Oregon of 23 days.  Other authors reported
that females fledge at approximately 27 days and males fledge at
approximately 24 days after hatching [9,14].  In an Oregon study, 70 to
100 percent of hatched young survived to fly [44].  The fledglings
remain near the nest area and are fed by both parents for at least 21
and up to 50 days [39,42,50].  Food delivery by the parents decreases
markedly at 42 to 47 days [39].  Juvenile sharp-shinned hawks go through
first molt and acquire adult plumage at just over 1 year of age [23].

Fall Migration:  Most sharp-shinned hawks in northern portions of the
breeding range migrate; birds that remain in the far north over the
winter are mostly juveniles, and do not usually survive the winter.
Most southwestern nesting sharp-shinned hawks also leave nesting
territories on a seasonal basis, but these birds probably do not travel
extensively [39].  Sharp-shinned hawks form large flocks during
migration [15] and often follow migrating flocks of songbirds.  Migration
activity is initiated from late August to October [35].  In Maryland,
fall migration occurs from September 1 to November 25 [48].

Breeding Age and Longevity:  Some sharp-shinned hawks first breed as
yearlings, but most do not breed until later [39].  Sharp-shinned hawk
ages of up to 12 years have been recorded; however, few sharp-shinned
hawks live longer than 5 years [39,50].

Mortality:  Major identifiable causes of sharp-shinned hawk mortality
include "road kill" and predators [25].  Evans and Rosenfield [8]
reported sharp-shinned hawk mortality from collision with windows.  In
the first half of this century, a large number of sharp-shinned hawks
were shot during migration (large flocks were easy targets); hawks are
now under legal protection so this threat is greatly reduced [45].
These hawks are still shot in the belief that they represent a threat to
domestic fowl or to songbirds [8,39].  Juvenile mortality is highest in
fall and winter.  However, almost half of mortality in older birds
occurs in spring, apparently caused by the rigors of spring travel, and
occurs mostly among females [39].


PREFERRED HABITAT : 
Sharp-shinned hawks breed in coniferous forests adjacent to other types
of stands; prey is usually more plentiful in mixed or patchy forests
than in large continuous stands of conifers [39].

Nesting:  Sharp-shinned hawk nests are built within the canopy rather
than below it.  Nest trees typically have dense foliage and are usually
conifers.  In Utah, some sharp-shinned hawk nests were built in diseased
deciduous trees that had abnormally dense foliage [40].  In Missouri,
nests were typically built in shortleaf pine or in Virginia pine (Pinus
virginiana) trees [54].  In canyons, nest trees are usually 165 to 330
feet (50-100 m) upslope from a stream [27,42].  In northwestern Oregon,
most nest trees were on gentle to moderate slopes (15-37%) with
northerly exposures; nest trees in eastern Oregon were on slopes ranging
from 8 to 47 percent [43].  Nests are occasionally built in rock
crevices or hollow trees [50].  In Oregon, sharp-shinned hawks nest from
near sea level to near timberline [42]; Nests were found from 396 feet
(120 m) to 6,633 feet (2,010 m) elevation [43].

Nesting habitat for sharp-shinned hawks usually consists of dense stands
of trees with a well developed canopy (canopy cover of 60% or more) and
a dense understory [27].  In Oregon, sharp-shinned hawks breed in young
(30- to 70-year-old), mature (80- to 190-year-old), and old-growth (over
190 years) forest [20].  In the Sierra Nevada, mixed conifer forests are
suitable habitat for sharp-shinned hawks.  Seral stages and cover
classes of suitable nesting habitat are as follows:  pole-medium tree
stage with 40 to 69 percent canopy cover, pole-medium tree stage with 70
percent or more canopy cover, and large tree stage with 70 percent or
more canopy cover [53].  In western forests, sharp-shinned hawks breed
in dense, young (25- to 50-year-old), even-aged second-growth stands with
single-layered canopies [27], and in 40- to 60-year-old even-aged
conifer stands [5,42].  In the Inland Northwest, sharp-shinned hawks
breed in pole-sapling, young, and mature mixed conifer forests, but not
in shrub-seedling stands or in old-growth forests [46].  In Idaho,
between May and August, sharp-shinned hawks were usually observed in
open riparian habitat or in parklike stands of coniferous forest.
However, it was noted that these hawks are difficult to observe in the
dense forests in which nests are built [52].

In Oregon, mean stand density of nest sites was 472 trees per acre
(1,180 trees/ha).  Typical forest structure for Oregon nest sites is an
overstocked stand with a shallow canopy and many dead limbs below the
live crowns [42].  In Oregon, nest sites (described as the area used by
a nesting pair and fledglings including roosts and perches used to pluck
prey) averaged about 9.9 acres (4 ha).  The average nesting range in
Idaho was 0.33 square mile (0.85 sq km) [52] and in Wyoming was 0.44
square mile (1.1 sq km) [7].  In Oregon, minimum nesting territory size
was estimated as 0.4 square mile (1 sq km) [20].  Many nest sites had
limits coinciding with discrete boundaries between vegetative structures
or topographic features [42].

In Oregon, nest density was estimated as one nest per 6,792 acres (2,750
ha), with mean nearest conspecific neighbor distance of 2.5 miles (4.1
km) [44].  In Idaho, nest density was estimated as 4.2 pairs of
sharp-shinned hawks per 10 square miles (1.6 pairs per 10 sq km) [52].

Foraging:  Foraging habitat for sharp-shinned hawks includes nesting
habitat, but the hawks also forage in more open environments [27].  In
the Inland Northwest, sharp-shinned hawks feed in shrub-seedling stands
and in pole-sapling, young, mature, and old-growth mixed conifer forests
[46].  Sharp-shinned hawk habitat includes canyons, valleys, and
riparian areas [27].

Migration:  Concentrations of migrating sharp-shinned hawks have been
observed along the ridgetops of the Allegheny Mountains in the Ridge
and Valley Sections [48].  During migration sharp-shinned hawks will
occupy almost any type of habitat that contains trees or shrubs [10].

Wintering:  The sharp-shinned hawk is less specific in its habitat
preferences in winter than in summer, and occurs in almost any forested
or shrubby habitat including riparian areas, woodlands, farmlands, urban
areas, and other areas more open than nesting habitat [10].


COVER REQUIREMENTS : 
Nesting Cover:  Nests are almost always built in trees with very dense
foliage [10,39].

Foraging Cover:  Sharp-shinned hawks prefer perches with substantial
arboreal cover from which to spot and capture prey; however, these
perches are often located near open areas in which prey is more easily
spotted and pursued [27].


FOOD HABITS : 
Sharp-shinned hawks prey largely on small birds; typically, prey birds
are sparrow-sized but occasionally larger birds are taken [10].
Sharp-shinned hawks forage in open forest, on the forest floor, in
meadow grasses, and in bushy pastures [10,39].  A characteristic hunting
style is to spot prey from a well-hidden perch and then fly quickly out
to capture it.  The sharp-shinned hawk "is numero uno at sneak attack"
[39].  Other styles include speculative flight:  The sharp-shinned hawk
flies (flaps and glides) close to the ground, darting under branches or
across small openings and over brushfields or meadows.  The hawk can
turn rapidly to grasp small birds in flight, drop to catch them on the
ground, or grab prey that is perched.  Prey is often pursued into dense
foliage.  Top flight speed is 28 miles per hour (47 km/h) [10,14,39,59].

In Colorado, birds constituted 91.1 percent of the prey of 11 nesting
pairs of sharp-shinned hawks.  The most frequently taken bird species
included yellow-rumped warbler (Dendroica coronata), American robin
(Turdus migratorius), white-crowned sparrow (Zonotrichia leucophrys),
and dark-eyed junco (Junco hyemalis).  Yellow-rumped warblers, dark-eyed
juncos, and American robins were among the most abundant birds in the
area.  Small birds were eaten in proportion to their relative frequency
in dominant and secondary habitat types, but the proportion eaten was
different from relative abundance in limited habitats.  Mammals averaged
8.9 percent of prey taken; 60 percent of the mammals eaten were voles
(Clethrionomys, Microtus, and Phenacomys spp.) [24].

In North America, the most common bird species taken by sharp-shinned
hawks include American robin, starling (Sturnus vulgaris), catbird
(Dumetella carolinensis), house sparrow (Passer domesticus), towhees
(Pipilo spp.), sparrows (Aimophila spp., Spizella spp., and others), and
brown creeper (Certhia americana) [39,50].  Prey as small as Anna's
hummingbird (Calypte anna) and as large as northern bobwhite (Colinus
virginianus) and young domestic fowl have been reported.  Nestlings and
young birds are common prey items, including the young of gallinaceous
birds [3] and other predatory birds such as flammulated owls (Asio
flammeus) [34].  Occasionally, the sharp-shinned hawk preys on mice,
shrews, moles, young lagomorphs, bats, red squirrel (Tamiasciurus
hudsonicus), frogs, butterflies, grasshoppers, and moths [3,9,39].  In
southern Arizona, sharp-shinned hawks were frequently seen perched or
flying in habitat preferred by Gambel's quail and were assumed to
represent a major cause of Gambel's quail mortality [17].

Sharp-shinned hawks have been known to attack pileated woodpeckers
(Dryocopus pileatus), but it is unclear whether attacks are territorial
or prandial in intent [39].


PREDATORS : 
Nestling sharp-shinned hawks are preyed upon by other raptors including
Cooper's hawk (Accipiter cooperi) and northern goshawk (A. gentilis)
[3].


MANAGEMENT CONSIDERATIONS : 
Sharp-shinned hawk populations are fairly stable in the United States,
although the species is endangered in some states [10,23].  The
sharp-shinned hawk is uncommonly seen except in the extreme southeastern
United States and in Canada [39].  It is uncommon in New England during
the breeding season, and uncommon to rare in winter [9].

The decline of sharp-shinned hawk populations in the eastern United
States in the 1960's and 1970's was attributed to the thinning effect of
DDT on eggshells [50].  Most populations appear to be in recovery from
declines in the early 1970's and 1980's [10], although in some regions
they continue to decline.  Sauer and others [47] summarized breeding
bird surveys and banding studies from 1966 to 1987; in the central
region sharp-shinned hawks declined by 2.3 percent per year in breeding
bird surveys (38 survey routes).  Rosenfield and others [45] noted that
sharp-shinned hawks are difficult to census, particularly during
breeding season when they spend most of the time below the canopy in
dense forests.

Land use impacts on raptor habitat include reduction and fragmentation
of habitat and reduction in prey availability [38].

The sharp-shinned hawk is rated as a generalist with respect to
microhabitat (is not associated with a specific microhabitat), a
generalist in response to edge (uses both interiors and edges), and has
a positive response to suitable habitat patch size.  It is rated as 18
on a scale of 20 to sensitivity to landscape change, indicating that it
is very sensitive to landscape change [20].  Reynolds [42] also stated
that sharp-shinned hawks are vulnerable to changes in forest stands
resulting from timber harvesting.  The sharp-shinned hawk showed extreme
sensitivity to forest fragmentation west of the Cascade Range in
Washington, Oregon, and California; it was not found in areas that were
broken up into small patches of forest [21].

A table showing the effects of different logging practices on raptors in
the northeastern United States indicated that any logging has negative
effects on sharp-shinned hawk nesting.  Selection cuts and clearcuts,
however, are beneficial for home range (i.e., foraging) and local
population size, probably due to increased availability of prey [37].
Munro and Cowan [36] noted that the sharp-shinned hawk was present in
regenerating cutover and burned areas in British Columbia.  It seems
likely that the hawks were foraging in these areas due to an influx of
granivorous birds, but nesting elsewhere.

General recommendations for forest timber management to preserve sharp-
shinned hawk habitat include small clearcuts only (that is, no large
clearcuts), a mosaic of different-aged stands, and most importantly,
the maintenance of large uncut tracts of mature timber [2,5].  During
the breeding season, large areas around active nest sites need to be
left undisturbed [5].  Reynolds [42] recommended uncut areas of a
minimum of 9.9 acres (4 ha) around active nests in Oregon.  In addition,
management of raptor habitat needs to take into account nest site
turnover; sharp-shinned hawks usually build new nests every year.
Neither active nor prospective nest sites should be precommercially or
commercially thinned.  To maintain nesting densities of sharp-shinned
hawks at the level found in Oregon, currently suitable nest sites should
be provided at a density of approximately 20 sites per township (36
square miles [90 sq km]).  Further study is needed to determine the size
and shape of home ranges and the extent to which these habitats are used
for foraging.  In addition, studies are needed to determine appropriate
densities for nest sites in other localities [42].

The sharp-shinned hawk is listed as a species that depends on forests
and undisturbed riparian habitats, and is likely to decline or be
eliminated from areas that are converted to agricultural use.
Sharp-shinned hawks occasionally use agricultural areas in winter; the
response to conversion of winter habitat to agricultural use is likely
to depend on the extent of human activity and availability of prey [57].
Mansell [35] noted the presence of a sharp-shinned hawk in and near a
25-year-old abandoned field (presumably in the eastern United States),
but sharp-shinned hawks had not been present while the field was in
cultivation, despite the presence of domestic fowl.

Grimm and Yahner [18] suggested that in the Northeast, sharp-shinned
hawks may respond best to selection cuts favoring conifers growing under
an overstory of hardwoods.  Nearby patches of early successional
vegetation produced by clearcuts may also represent habitat improvement,
if silvicultural treatments are not extensive in size [37].

In Rhode Island, migrant sharp-shinned hawks were observed using placed
perches consisting of dead trees, but were never observed using
artificial perches constructed of milled timber [41].


REFERENCES : 
NO-ENTRY

Related categories for Wildlife Species: Accipiter striatus | Sharp-Shinned Hawk