Swainson's Hawk

More info for the terms: grassland, shrubs

The Swainson's hawk breeds in open grasslands, sagebrush (Artemisia
spp.), shrub-steppe, oak (Quercus spp.) woodlands, open pine (Pinus
spp.)-oak woodlands, pinyon-juniper (Pinus spp.-Juniperus spp.)
woodlands, and cultivated lands [1,3,6,16,40].  In California the
Swainson's hawk favors open blue oak (Quercus douglasii) savannahs and
gray pine (Pinus sabiniana)-oak woodlands [35].  In the Central Valley
of California, populations of Swainson's hawks frequently nest and roost
in riparian communities dominated by valley oak (Quercus lobata),
cottonwoods (Populus spp.), California sycamore (Platanus racemosa), and
willows (Salix spp.)  [22,33].  Foraging habitat for Swainson's hawks in
California includes native grassland communities of oat (Avena spp.),
brome grass (Bromus spp.), ryegrass (Elymus spp. and Lolium spp.), and
barley (Critesion spp.) [33]. West of Laramie, Wyoming, Dunkle [15]
reported that breeding habitat of the Swainson's hawk included irrigated
sedge meadows, shortgrass plains with some sagebrush, and black
greasewood (Sarcobatus vermiculatus) [15].

In the Great Basin, the Swainson's hawk is often found nesting in
juniper-sagebrush and prairie habitats [33].  In Arizona, the Swainson's
hawk generally occurs in sparse semidesert grasslands, plains
grasslands, Great Basin grasslands, and Chihuahuan Desert scrub often
mixed with a few species of shrubs including yucca (Yucca spp.),
creosotebush (Larrea tridentata), mesquite (Prosopis spp.), and fourwing
saltbrush (Atriplex canescens).  In New Mexico and Texas, breeding
Swainson's hawk occur in various types of grasslands including
grasslands with sand shinnery oak (Q. havardii), and are occasionally
found in Chihuahuan Desert scrub.  In Oklahoma, Swainson's hawk breed
primarily in grasslands [6].

The Swainson's hawk sometimes nests in intensively cultivated areas
[4,5,20].  Of the large raptors breeding in northern Colorado, only the
Swainson's hawk regularly nested near cultivated lands [20].

Swainson's hawk

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United States and Canada is available at NatureServe.

More info for the terms: cover, density, selection

Swainson's hawk nests are often built in trees that provide shade for
the nest but also afford a good view of the surrounding terrain [33].

The Swainson's hawk is a more efficient predator in open areas than in
areas with high vegetative cover [5].  Bechard [5] found that vegetative
cover is more important than prey abundance in the selection of hunting
sites by the Swainson's hawk.  In Whitman County, Washington, the
Swainson's hawk foraged at sites where vegetative height and density had
been reduced, even though other areas had higher prey density [5].
Alfalfa field use by Swainson's hawk in northern California increased
dramatically during monthly harvests that reduced vegetative heights
[38].

The breeding range of the Swainson's hawk is restricted primarily to
western North America from interior Alaska and western Canada south
into northern Mexico [12,21].  The Swainson's hawk winters primarily on
the pampas of southern South America, irregularly north to Costa Rica
and Panama, and sometimes north to the southwestern United States and
southern Florida [1,12,21].  During migration the Swainson's hawk occurs
regularly in most of the central states and Canadian provinces, and
rarely, east along the Gulf Coast to Florida. It is occasionally a fall
migrant through the Florida Keys.  The Swainson's hawk is occasionally
found in northeastern North America from southern Ontario, southern
Quebec, New York, and Massachusetts south to Virginia [1].

More info for the term: grassland

The Swainson's hawk is a versatile and opportunistic predator on
relatively small prey [6].  The Swainson's hawk feeds on small mammals,
large insects, birds, and reptiles [9,14,31,35].  During the breeding
season, the Swainson's hawk primarily preys on small mammals, especially
young ground squirrels (Spermophilus spp.), pocket gophers (Thomomys
spp.), and some microtines [15,20,31,32].  During migration
invertebrates often make up over 90 percent of the Swainson's hawk's
diet [31].

In a North Dakota study, Swainson's hawks preyed primarily on northern
pocket gopher (Thomomys talpoides), Richardson's ground squirrel
(Spermophilus richardsonii), meadow vole (Microtus pennsylvanicus), and
thirteen-lined ground squirrel (S. tridecemlineatus) [20].  To a lesser
extent Swainson's hawks also ate western meadow lark (Sturnella
neglecta), chestnut-collared longspur (Calcarius ornatus), sharp-tailed
grouse (Tympanuchus phasianellus), short-eared owl (Asio flammeus),
American kestrel (Falco sparverius), blue jay (Cyanocitta cristata),
and rock dove (Columba livia) [20].  Toads (Bufo spp.) and various
lizards, mostly desert grassland whiptail (Cnemidophorous uniparens)
and spiny lizards (Sceloporus spp.), were commonly taken by nesting
Swainson's hawk in Arizona.  Mammals, particularly cottontails
(Sylvilagus spp.), ground squirrels, and kangaroo rats (Dipodomys spp.),
were the most common food items brought to Swainson's hawk nestlings in
New Mexico [6].  Rabbits comprised between 40 and 80 percent of the diet
of Swainson's hawk nestlings in New Mexico [7].

More info for the terms: fire suppression, forest, grassland

The Swainson's hawk occurs in the following four major fire-dependent
plant associations in the western United States:  grassland, semidesert
grass-shrub, sagebrush grass, and pinyon-juniper [26].

Although fire may reduce potential nest trees, it may enhance the
foraging habitat of Swainson's hawks.  Fires that reduce vegetation
height and create open areas probably increase hunting efficiency by
Swainson's hawks.  Open-habitat raptors such as the Swainson's hawk use
scattered patches of woody vegetation near open foraging areas for
nesting and perching.  However, where extensive invasion of woody
species has occurred, Swainson's hawk foraging habitat may be reduced.
The Swainson's hawk is favored by fires that reduce pinyon-juniper
woodlands [26].  Raptors associated with pinyon-juniper woodlands depend
upon edges of openings created by fire and scattered islands of unburned
woodlands [13].  Fire suppression in pinyon-juniper habitats of the
Great Basin of California may have reduced suitable Swainson's hawk
habitat in this area [26].

Regular burning helps to maintain habitat for many prey species of
Swainson's hawk [13,25].  Several studies indicate that many prey
populations increase rapidly subsequent to burning in response to
increased food availability [13].  Fire suppression in grasslands was
detrimental to small bird and mammal populations due to organic matter
accumulation and reduced plant vigor [36].  The Swainson's hawk has been
observed hunting on recently burned areas in Colorado county, Texas [2].
On the Bridger Teton National Forest, Swainson's hawks were more
commonly observed using a high-severity fall burn than a low-severity
spring burn in the same area [27].

More info on this topic.

This species is known to occur in association with the following cover types (as classified by the Society of American Foresters):

    66  Ashe juniper - redberry (Pinchot) juniper
    67  Mohrs (shin) oak
    68  Mesquite
   203  Balsam poplar
   217  Aspen
   220  Rocky Mountain juniper
   221  Red alder
   222  Black cottonwood - willow
   233  Oregon white oak
   235  Cottonwood - willow
   236  Bur oak
   238  Western juniper
   239  Pinyon - juniper
   240  Arizona cypress
   241  Western live oak
   242  Mesquite
   246  California black oak
   249  Canyon live oak
   250  Blue oak - Digger pine
   252  Paper birch
   255  California coast live oak

More info on this topic.

This species is known to occur in the following ecosystem types (as named by the U.S. Forest Service in their Forest and Range Ecosystem [FRES] Type classification):

More info for the term: shrub

FRES28 Western hardwoods
FRES29 Sagebrush
FRES30 Desert shrub
FRES31 Shinnery
FRES33 Southwestern shrubsteppe
FRES34 Chaparral-mountain shrub
FRES35 Pinyon-juniper
FRES36 Mountain grasslands
FRES37 Mountain meadows
FRES38 Plains grasslands
FRES39 Prairie
FRES40 Desert grasslands
FRES41 Wet grasslands
FRES42 Annual grasslands

More info on this topic.

This species is known to occur in association with the following plant community types (as classified by Küchler 1964):

More info for the terms: cactus, shrub, woodland

   K023  Juniper - pinyon woodland
   K024  Juniper steppe woodland
   K026  Oregon oakwoods
   K027  Mesquite bosque
   K030  California oakwoods
   K031  Oak - juniper woodlands
   K032  Transition between K031 and K037
   K033  Chaparral
   K034  Montane chaparral
   K035  Coastal sagebrush
   K037  Mountain-mahogany - oak scrub
   K038  Great Basin sagebrush
   K039  Blackbrush
   K040  Saltbush - greasewood
   K041  Creosotebush
   K042  Creosotebush - bursage
   K043  Paloverde - cactus shrub
   K044  Creosotebush - tarbush
   K045  Ceniza shrub
   K047  Fescue - oatgrass
   K048  California steppe
   K050  Fescue - wheatgrass
   K051  Wheatgrass - bluegrass
   K053  Grama - galleta steppe
   K054  Grama - tobosa prairie
   K055  Sagebrush steppe
   K056  Wheatgrass - needlegrass shrubsteppe
   K057  Galleta - three-awn shrubsteppe
   K058  Grama - tobosa shrubsteppe
   K059  Trans-Pecos shrub savanna
   K060  Mesquite savanna
   K061  Mesquite - acacia savanna
   K062  Mesquite - live oak savanna
   K063  Foothills prairie
   K064  Grama - needlegrass - wheatgrass
   K065  Grama - buffalograss
   K066  Wheatgrass - needlegrass
   K067  Wheatgrass - bluestem - needlegrass
   K068  Wheatgrass - grama - buffalograss
   K069  Bluestem - grama prairie
   K070  Sandsage - bluestem prairie
   K071  Shinnery
   K072  Sea oats prairie
   K074  Bluestem prairie
   K075  Nebraska Sandhills prairie
   K076  Blackland prairie
   K077  Bluestem - sacahuista prairie
   K083  Cedar glades
   K085  Mesquite - buffalograss
   K086  Juniper - oak savanna
   K087  Mesquite - oak savanna
   K088  Fayette prairie

More info for the term: density

Swainson's hawk populations have declined over much of their breeding
range due to habitat loss from cultivation, removal of riparian areas,
and removal of shelterbelts [14,31].  Nest site availability may limit
occurrence and breeding density of Swainson's hawk [6].  Schmutz and
others [34] reported that the nesting density of the Swainson's hawk
increased significantly following the erection of 98 artificial nest
platforms in an experimental study plot.  When roads, pipelines, or
other surface facilities are constructed, trees taller than 10 feet (3
m) with a d.b.h. of 2 inches (5 cm) or more should be conserved.  If
destruction of potential nest trees cannot be avoided, they should be
replaced with artificial nest platforms [7].  Within treeless expanses,
constructing artificial nest platforms or planting trees may also benefit
Swainson's hawk populations [6].  Additionally, establishing and
enhancing small wooded areas in the nesting habitat, and protecting
habitat used by the prey base, may benefit the Swainson's hawk [10,39].

The Swainson's hawk is more tolerant of human disturbance than other
hawks and will often nest close to occupied houses [7,14].  However,
intensive human activity in a small area near an active Swainson's hawk
nest would likely result in nest abandonment and breeding failure at
that site [7].

Swainson's hawk is sometimes eaten by people in South America.  Large
numbers are taken from communal roosting areas and killed.  This
activity could have a significant effect on populations that nest in
North America [21].  Additionally, the use of biocides in North,
Central, and South America may have an effect on Swainson's hawk
populations.  The Swainson's hawk may accumulate high pesticide levels
via food-chain concentration [31].

AK
AZ
CA
CO
CT
DE
FL
ID
IL

IA
KS
LA
MD
MA
MT
NE
NV
NH

NJ
NM
NY
ND
OH
OK
OR
PA
RI

SD
TN
TX
UT
VA
WA
WY




AB
BC
MB
NT
ON
PQ
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YT



MEXICO

Large raptors including great horned owl (Buteo virginianus) and golden
eagle (Aquila chrysaetos), and coyote (Canis latrans), bobcat (Lynx
rufus), and striped skunk (Mephitis mephitis) have been known to kill
Swainson's hawk nestlings and fledglings or destroy clutches
[7,11,15,31,38].  Crows (Corvus spp.) sometimes destroy clutches
[15,31].

More info for the terms: shrubs, tree, tundra

The Swainson's hawk inhabits mostly semiopen to open areas in tundra,
valleys, plains, dry meadows, foothills, and level uplands at low to
middle elevations [1,31,40].

Nesting habitat - The Swainson's hawk nests almost exclusively in trees
[37] and will nest in almost any tree species of suitable size (taller
than 10 feet [3 m] with a d.b.h. of 2 inches [5 cm] or more) [6,7].
Nests are constructed in isolated trees (dead or live), in trees in
wetlands and along drainages, or in windbreaks in fields and around
farmsteads [6,12,31].  The Swainson's hawk builds nests from 4 to 100
feet (1.2-30.4 m) above the ground [12,14,35].  They sometimes add to an
existing black-billed magpie (Pica pica) nest [31].  The Swainson's hawk
occasionally nests in shrubs, on the crossbars of telephone poles, or on
the ground, low cliffs, rocky pinnacles, or cutbanks [6,12,31].

In the Central Valley of California, the majority of Swainson's hawk
nests and territories are located in or near riparian systems.  Nests
are found most often in cottonwoods and oaks [33].  In Whitman County,
Washington, Swainson's hawk nests were constructed in black locust
(Robinia pseudoacacia), cherry (Prunus spp.) and hawthorn (Crataegus
spp.) trees [5].  Of 48 Swainson's hawk nests on the Laramie Plains,
Wyoming, 43 were in narrowleaf cottonwood (Populus angustifolia),
peachleaf willow (Salix amygdaloides), or other willows.  None of the
few buttes in the area were used for nesting [15].  In the Centennial
Valley of Montana, Swainson's hawks nest extensively in willows [32].
At 234 Swainson's hawk nest sites in North Dakota, eastern cottonwood
(Populus deltoides) was the most common tree species used (45%).  Other
species included Chinese elm (Ulmus parvifolia), 22 percent; peachleaf
willow, 13 percent; boxelder (Acer negundo), 12 percent; and green ash
(Fraxinus pennsylvanica), 7 percent.  American elm (U. americana) and
Russian olive (Elaeagnus angustifolia) accounted for the remaining 1
percent [20].  In the Lower Sonoran Desert of New Mexico, the Swainson's
hawk often nests and roosts on large yucca plants [30].  In the
southwestern United States, mesquite is commonly used [6].

Foraging habitat - The Swainson's hawk generally forages in open
habitats with short vegetation containing small mammals, reptiles,
birds, and insects [6,40,38].  During the nesting season the Swainson's
hawk usually forages within 1.9 miles (3 km) of the nest.  The
Swainson's hawk has a home range of approximately 3.5 square miles (9 sq
km) [40].  Although the Swainson's hawk does search for prey from
elevated perches, it relies much more on aerial foraging.  Consequently,
it is not tied to habitats containing an abundance of perches, and often
occupy habitats with few or no perches except the nest tree [23].

Winter habitat - The Swainson's hawk generally spends the winter south
of the United States [1,12,31]; no information is available in the
English literature on its habitat in Central and South America.

More info on this topic.

This species can be found in the following regions of the western United States (according to the Bureau of Land Management classification of Physiographic Regions of the western United States):

    1  Northern Pacific Border
    2  Cascade Mountains
    3  Southern Pacific Border
    4  Sierra Mountains
    5  Columbia Plateau
    6  Upper Basin and Range
    7  Lower Basin and Range
    8  Northern Rocky Mountains
    9  Middle Rocky Mountains
   10  Wyoming Basin
   11  Southern Rocky Mountains
   12  Colorado Plateau
   13  Rocky Mountain Piedmont
   14  Great Plains
   15  Black Hills Uplift
   16  Upper Missouri Basin and Broken Lands

The currently accepted scientific name for the Swainson's hawk is Buteo
swainsoni Bonaparte [1]. There are no recognized subspecies or races.

More info for the term: tree

Age at sexual maturity - Swainson's hawk are generally sexually mature
at 2 years of age [31].

Nesting season - The Swainson's hawk arrives on its breeding grounds
later than most raptors [31].  The nesting season generally occurs from
March to October depending on geographic area [14,21,35].  In
California, the Swainson's hawk breeds from late March to mid-August,
with peak activity from late May to late July.  In Nevada, it breeds
from April to October [21].  In Montana, the breeding season is from May
to September [14].
 
Clutch size and incubation - The Swainson's hawk lays two to four eggs,
with two most common [14,21,31,35].  The eggs are incubated for 28 to 35
days [14,21,31].  The Swainson's hawk may lay a replacement clutch if
the first clutch is destroyed [31].

Fledging - Nestlings fledge in 35 to 44 days [21,31].  Fledglings
continue to be fed by the adults and remain within the nesting territory
for 14 to 21 days after fledging; they often return to the nest tree to
roost [21].

Migration - The Swainson's hawk travels in large flocks (sometimes
containing over 100 individuals) from the nesting areas south to their
winter grounds in South America [6,21,31].

Peak fall migration clears the southern plains states and southern Texas
by early October.  The Swainson's hawk arrives in Central America the
last 3 weeks of October to early November; arrival in Argentina is
reported as late November.  Average dates for spring migration of the
Swainson's hawk are mid-March in Panama, the last 3 week of March in
Costa Rica, the last half of March and first week of April in the state
of Veracruz, Mexico, and early April in southern Texas [31].

Longevity - The Swainson's hawk probably seldom lives longer than 16
years [31].

Not listed [43]

More info for the terms: fire regime, grassland, herbaceous

Prescribed fire can be beneficial to Swainson's hawk populations by
enhancing habitat and increasing the prey base [13,25].  Burning in
grasslands where scattered trees are retained benefits Swainson's hawk
populations, particularly in areas where nesting sites are limited.
Prescribed burning plans should strive for creation of maximum
interspersion of openings and edge, with high vegetative diversity.
Habitats should be maintained in a random mosaic.  In most cases,
burning plans must be integrated with proper range management.
Reseeding of perennial grasses as well as rest from livestock grazing
may be necessary to achieve desired goals.  Burning should be deferred
until nesting is completed in areas where impact to breeding Swainson's
hawk may occur [13].


An extensive body of research has been published on fire effects on animals
in semidesert grassland, oak savanna, and Madrean oak woodlands of southeastern
Arizona, including the response of Swainson's hawk to fire. See the Research Project Summary of this work for more information on
Swainson's hawk and more than 100 additional species of birds, small
mammals, grasshoppers, and herbaceous and woody plant species.

FIRE REGIMES :
Find fire regime information for the plant communities in which this
species may occur by entering the species name in the FEIS home page under
"Find FIRE REGIMES".