dcsimg

Lifespan, longevity, and ageing

provided by AnAge articles
Maximum longevity: 19.6 years (wild) Observations: Maximum longevity in banded birds was 19.6 years (Blumstein and Moller 2008).
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Joao Pedro de Magalhaes
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Trophic Strategy

provided by Animal Diversity Web

The Swainson's Hawk is somewhat of a generalist, and eats whatever it can find. During its time in North America, its diet consists of insects, small mammals and birds, and occasional reptiles and amphibians. When these birds migrate to the Argentina area, they feed mainly on insects like grasshoppers and crickets (Brown 1996, TPWD 1997).

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Stabler, K. 2000. "Buteo swainsoni" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Buteo_swainsoni.html
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Kara Stabler, Southwestern University
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Stephanie Fabritius, Southwestern University
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Benefits

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The Swainson's Hawk is of special importance to farmers, both in North and South America. Some Swainson's Hawks will live entirely on insects and rodents that it catches in crop fields, thus alleviating some crop destruction for farmers. This species is also important to scientists as they can study the ecological details of its massive migration of over 5,000 miles (Brown 1996, AID 1997, Line 1996).

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Stabler, K. 2000. "Buteo swainsoni" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Buteo_swainsoni.html
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Kara Stabler, Southwestern University
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Stephanie Fabritius, Southwestern University
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Conservation Status

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This species of hawk is on the list of Federal Species of Concern, and is also considered threatened by the state of California. The primary cause of this concern is the massive killing of more than 20,000 Swainson's Hawks by pesticides used in the Argentina agricultural areas. In order to help these hawks recover, the use of deadly pesticides by Argentinian farmers must be stopped. Although the farmers are in support of saving the birds, this recovery effort is proving to be a daunting task (Brown 1996, Line 1996).

US Migratory Bird Act: protected

US Federal List: no special status

CITES: appendix ii

State of Michigan List: no special status

IUCN Red List of Threatened Species: least concern

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Stabler, K. 2000. "Buteo swainsoni" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Buteo_swainsoni.html
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Kara Stabler, Southwestern University
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Stephanie Fabritius, Southwestern University
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Behavior

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Perception Channels: visual ; tactile ; acoustic ; chemical

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Stabler, K. 2000. "Buteo swainsoni" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Buteo_swainsoni.html
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Kara Stabler, Southwestern University
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Stephanie Fabritius, Southwestern University
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Distribution

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The Swainson's Hawk, -Buteo swainsoni-, spends most of the year in the western United States extending into southwest Canada and south to west Texas. In the winter months, these birds migrate over Central America to the La Pampas region of Argentina (Brown 1996, TPWD 1997).

Biogeographic Regions: nearctic (Native ); neotropical (Native )

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Stabler, K. 2000. "Buteo swainsoni" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Buteo_swainsoni.html
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Kara Stabler, Southwestern University
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Stephanie Fabritius, Southwestern University
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Habitat

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This hawk prefers open grasslands and desert-like habitats. It is common to see this hawk perched on a fence post in a prairie or open range. The Swainson's Hawk also inhabits agricultural areas, and is known to follow farmer's tractors in search of insect or rodent prey (Brown 1996, AID 1997).

Terrestrial Biomes: desert or dune ; savanna or grassland ; chaparral

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Stabler, K. 2000. "Buteo swainsoni" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Buteo_swainsoni.html
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Kara Stabler, Southwestern University
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Stephanie Fabritius, Southwestern University
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Life Expectancy

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Range lifespan
Status: wild:
19.5 (high) years.

Average lifespan
Status: wild:
235 months.

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Stabler, K. 2000. "Buteo swainsoni" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Buteo_swainsoni.html
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Kara Stabler, Southwestern University
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Stephanie Fabritius, Southwestern University
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Morphology

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This hawk's most unique feature is its variation in color. The light color morph includes white patches on the forehead, the throat and the belly. The rest of the body is a dark brown. The dark color morph, which is the less common type, includes an entirely dark brown body with only a white patch under the tail. Other variations between these two distinct extremes have been observed. These hawks vary in length from 19 to 22 inches, and have a wingspan of 47 to 57 inches. An average weight for a male is 1.8 pounds, while the average for the female is almost 2.5 pounds. This bird is commonly confused with a Red-tailed hawk, but the Swainson's Hawk has a longer wingspan, more variation in color, and flies in a slight dihedral pattern (Brown 1996, AID 1997).

Other Physical Features: endothermic ; bilateral symmetry

Average mass: 980.64 g.

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Stabler, K. 2000. "Buteo swainsoni" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Buteo_swainsoni.html
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Kara Stabler, Southwestern University
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Stephanie Fabritius, Southwestern University
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Reproduction

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The Swainson's Hawk starts the breeding season by building nests in March and April. The nest are usually found in trees, shrubs, on the ground, or on top of utility poles. These hawks are mostly mongamous, so a breeding pair may return to a previous nesting site. These birds become highly territorial towards their nest and their mate during this time of the year. When the nest is complete, the female lays 2 to 4 whitish-colored eggs with brown flecks. The male usually helps the female with the incubation, which lasts for about 30 days. The young hatch between March and July, and stay in the nest for another 30 days. While most juveniles migrate the following winter with their parents, there are some groups that do not migrate their first winter (Brown 1996, TPWD 1997).

Key Reproductive Features: iteroparous ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; oviparous

Average time to hatching: 31 days.

Average eggs per season: 3.

Average age at sexual or reproductive maturity (male)
Sex: male:
730 days.

Average age at sexual or reproductive maturity (female)
Sex: female:
730 days.

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Stabler, K. 2000. "Buteo swainsoni" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Buteo_swainsoni.html
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Kara Stabler, Southwestern University
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Stephanie Fabritius, Southwestern University
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Brief Summary

provided by EOL authors
Swainson’s Hawk (Buteo swainsoni) is a medium-sized slender hawk (Crow-sized), with long, pointed wings and a long tail. Measurements include: length 17-22 inches (43-56 cm); wingspan 47-54 inches (120-137 cm); weight 1.3-2.7 lb (595-1240 g). Females slightly larger than males. Plumage extremely variable, but most individuals are recognizable. Adult-sides of the head and entire upper parts dark blackish brown; feathers obscurely edged with paler brown to cinnamon. Tail gray, basally whitish, with a narrow white tip, and several indistinct blackish bars, the last one broader. Primaries blacker than back; becoming paler basally. Throat white; breast brownish chestnut with weak black shaft streaks. Belly and legs dull white; indistinctly mottled and barred with brown to rufous. Under-wings pale with conspicuous dark marks at ends of coverts. Dark phase more or less sooty all over. Wing and tail as in normal phase, except that wing linings are much more marked with blackish. Rufous phase lighter brown below than the dark phase; and somewhat barred and blotched below with rusty brown. Intermediates occur between all the phases. Eye dark brown; cere pale greenish yellow; bill blackish; legs wax yellow (Brown et al 1968). The immature plumage, which is worn for two years, is similar to that of adults in its two- toned underwing and finely barred tail, but young birds have a spotted and streaked breast that at times shows a hint of a darker pattern, and the head shows a definite buffy streak above the eye and on the cheek, with a dark eye line and malar stripes. This typical pattern occurs on perhaps half the Swainson’s Hawk encountered in Arizona, and if color pattern alone is used for identification, the other half will be mis-identified. (Glinski 1998). Found only in the New World; it breeds in North America, in the Great Plains and arid regions, north sparingly to interior Alaska, and south to northern Mexico, and winters in South America. The normal winter range is the Pampas of Argentina, and it has been assumed that any found elsewhere at that season are casuals, probably unable to make the long migration (Brown et al 1968). Gives a descending shrill, plaintive whistle, kreeeeeeer, trailing off at end. In flight, shows profile like that of Turkey Vulture; the wings are held in a dihedral, or "V", position, which promotes aerodynamic stability in open landscapes where wind can interfere with flight close to the ground. Highly migratory, often seen in large flocks on spring and fall flights. During the breeding season, a soaring, open country hunter. Sometimes hunts high in the air, but more frequently courses low over prairie. Rarely observed flying low at high speed as Ferruginous Hawk does. Often hunts from perches such as tree limbs, poles or posts, rocks, and elevated ground.

Associated Plant Communities

provided by Fire Effects Information System Animals
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].
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Tesky, Julie L. 1994. Buteo swainsoni. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/

Common Names

provided by Fire Effects Information System Animals
Swainson's hawk
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Tesky, Julie L. 1994. Buteo swainsoni. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/

Conservation Status

provided by Fire Effects Information System Animals
Information on state-level protected status of animals in the
United States and Canada is available at NatureServe.
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Tesky, Julie L. 1994. Buteo swainsoni. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/

Cover Requirements

provided by Fire Effects Information System Animals
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].
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bibliographic citation
Tesky, Julie L. 1994. Buteo swainsoni. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/

Distribution

provided by Fire Effects Information System Animals
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].
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Tesky, Julie L. 1994. Buteo swainsoni. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/

Food Habits

provided by Fire Effects Information System Animals
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].
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Tesky, Julie L. 1994. Buteo swainsoni. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/

Habitat-related Fire Effects

provided by Fire Effects Information System Animals
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].
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Tesky, Julie L. 1994. Buteo swainsoni. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/

Habitat: Cover Types

provided by Fire Effects Information System Animals
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
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Tesky, Julie L. 1994. Buteo swainsoni. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/

Habitat: Ecosystem

provided by Fire Effects Information System Animals
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
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bibliographic citation
Tesky, Julie L. 1994. Buteo swainsoni. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/

Habitat: Plant Associations

provided by Fire Effects Information System Animals
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
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bibliographic citation
Tesky, Julie L. 1994. Buteo swainsoni. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/

Management Considerations

provided by Fire Effects Information System Animals
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].
license
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bibliographic citation
Tesky, Julie L. 1994. Buteo swainsoni. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/

Occurrence in North America

provided by Fire Effects Information System Animals

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
SK
YT



MEXICO


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bibliographic citation
Tesky, Julie L. 1994. Buteo swainsoni. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/

Predators

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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].
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Tesky, Julie L. 1994. Buteo swainsoni. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/

Preferred Habitat

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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.
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Tesky, Julie L. 1994. Buteo swainsoni. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/

Regional Distribution in the Western United States

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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
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Tesky, Julie L. 1994. Buteo swainsoni. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/

Taxonomy

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The currently accepted scientific name for the Swainson's hawk is Buteo
swainsoni Bonaparte [1]. There are no recognized subspecies or races.
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Tesky, Julie L. 1994. Buteo swainsoni. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/

Timing of Major Life History Events

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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].
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bibliographic citation
Tesky, Julie L. 1994. Buteo swainsoni. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/

U.S. Federal Legal Status

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Not listed [43]
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Tesky, Julie L. 1994. Buteo swainsoni. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/

Use of Fire in Population Management

provided by Fire Effects Information System Animals
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".
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bibliographic citation
Tesky, Julie L. 1994. Buteo swainsoni. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/

Swainson's hawk

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Swainson's hawk (Buteo swainsoni) is a large bird species in the Accipitriformes order. This species was named after William Swainson, a British naturalist. It is colloquially known as the grasshopper hawk or locust hawk, as it is very fond of Acrididae (locusts and grasshoppers) and will voraciously eat these insects whenever they are available.

Their breeding habitat is prairie and dry grasslands in western North America. They build a stick nest in a tree or shrub or on a cliff edge. This species is a long-distance migrant, wintering in Argentina; it has been recorded as a vagrant in neighboring Chile, in the island countries of the Dominican Republic, and Trinidad and Tobago, and in Norway.[1]

This species or its immediate predecessor is the ancestor of the Galápagos hawk, as demonstrated by recent research. Then later diverged from the mainland birds perhaps 300,000 years ago, a very short time in evolution.[2]

Description

Rufous-morph bird in Hereford, Arizona, on its way to the pampas

Swainson's hawk is a raptor and a medium-sized member of the genus Buteo. It broadly overlaps in size with the red-tailed hawk (B. jamaicensis), a related species found as a breeding resident almost throughout North America. Swainson's hawk is on average a little shorter in length, 43–56 cm (17–22 in) long, and weighs a bit less, 0.5–1.7 kg (1.1–3.7 lb).[3][4][5] However, Swainson's hawk has a slightly longer wingspan at 117–137 cm (46–54 in), with more slender, elongated wings, than the red-tailed hawk.[3] Female Swainson's hawks, at an average weight of 1.15 kg (2.5 lb), are somewhat larger and heavier than males, at an average of 0.81 kg (1.8 lb).[3] Among standard measurements, the wing chord is 36.2–42.7 cm (14.3–16.8 in), the tail is 18.5–23.4 cm (7.3–9.2 in), the tarsus is 6.2–8 cm (2.4–3.1 in) and the bill (from the gape) is 3–3.5 cm (1.2–1.4 in).[3] In flight, Swainson's hawk holds its wings in a slight dihedral; it tips back and forth slightly while soaring.

There are two main color variations. Over 90% of individuals are light-morph; the dark morph is most common in the far west of the range:[6]

  • Light-morph adults are white on the underparts with a dark, reddish "bib" on the chest and a noticeable white throat and face patch. The underwings, seen as the bird soars, have light linings (leading edge) and dark flight feathers (trailing edge), a pattern unique among North American raptors. The tail is gray-brown with about six narrow dark bands and one wider subterminal band. The upperparts are brown. Juveniles are similar but dark areas have pale mottling and light areas, especially the flanks, have dark mottling. The chest is pale with some darker marks. The subterminal band of the tail is less obvious. Birds in their first spring may have pale heads because of feather wear.
  • Dark-morph birds are dark brown except for a light patch under the tail. There is a rufous variant that is lighter on the underparts with reddish bars. The tails of both these forms resemble those of the light morph.

Range and migration

Swainson's hawk inhabits North America mainly in the spring and summer, and winters in South America. Breeding areas include south-central Alberta, central Saskatchewan, southwestern Manitoba, and west and southern Minnesota. They will breed as far north as east-central Alaska, and southwestern Yukon. Breeding continues south through the eastern parts of Washington and Oregon, locally to the central valley of California, Arizona, New Mexico, Colorado, and most of Texas. The eastern part of its range includes Minnesota, northwestern Iowa, most of Nebraska, Kansas, and Oklahoma, and all but eastern Texas. It periodically occurs in Iowa and rarely in northwestern Missouri, northern Illinois, and southwestern Wisconsin.

Swainson's hawk migration route.
30 birds were fitted with satellite tracking devices to produce this map

Small populations winter in southeastern Florida and along the Texas coast, probably having failed to find the way south around the Gulf of Mexico. Individuals reported north of these areas in winter (for example, on Christmas Bird Counts) are almost invariably misidentified buteos of other species. Swainson's hawks mostly winter on the pampas of South America in Argentina, Uruguay, and southern Brazil.[7] The populations of Swainson's hawks breeding in California's Central Valley also winter in western Mexico and central America.[8]

The Swainson's hawk is the second longest migrant of any North American raptor, after arctic nesting Peregrine falcons. The flight from breeding ground to South American pampas in southern Brazil or Argentina can be as long as 7,100 mi (11,400 km). Each migration can last at least two months.

They leave the breeding grounds from August to October. Fall migration begins each clear day on which a wind blows in the general direction of travel. Birds gain altitude by soaring in circles on a rising thermal and then set their wings and close their tails as they glide, slowly losing altitude until they find another thermal and rise with it. Thus, waves and small groups are strung out across the sky.

The birds gradually head southwards toward Central America where virtually the entire population funnels through the Isthmus of Panama. Concentrations over locations like Ancon Hill, Balboa, and Panama City are spectacular. In the Andes, it migrates along a narrow corridor and rarely strays off course; for example, it was only recorded in the Serranía de las Quinchas of Colombia – just 100 km (62 mi) or so off its usual migration route – in 2000/2001.[9]

In Brazil, migrating birds pass through the western states of Acre and Mato Grosso, while wintering birds may stray to the southern states of Paraná, Rio Grande do Sul and São Paulo. But surprisingly, the occasional Swainson's hawk — including birds one or two years of age — has also been recorded in the eastern states of Maranhão, Pará, Pernambuco, Piauí and Tocantins, thousands of kilometers away from their usual migration route and wintering grounds and sometimes in mid-summer. This suggests that individuals occasionally become lost during migration, and/or that they may spend a whole year in the tropical regions and range about, rather than just overwintering at one site.[10]

In Uruguay, the first dedicated studies show it to be not uncommon but patchily distributed across the country in winter. Notably, it had been underreported in Flores and Paysandú Departments, where it seems in fact to be a regular visitor. In recent years, the first birds were seen in early November, and some stayed until late February. Numbers increase throughout November and peak in December, when flocks of many dozen roam the open lands. But many stay only for a scant few weeks before leaving again.[11]

Spring migration broadens once the birds have passed through Mexico as they disperse through the breeding range. Migrant groups are noted in the southern U.S. states in March. The earliest Swainson's hawks arrive in southern Canada in late March, with migration peaking from mid April onwards.

Ecology

Soaring light-morph adult

The habitat of Swainson's hawk consists of open and semi-open country – deserts, grasslands and prairies – in both its breeding and wintering ranges. It favors wild prairie, hayfields, and pastures over wheat fields and alfalfa fields, which may offer its prey too much cover. It requires elevated perches for hunting and a supply of small mammals such as young ground squirrels as prey for its nestlings. The breeding distribution of Swainson's hawk is tied very closely to the distribution of various small mammals for this reason. In Saskatchewan, for example, the distribution of Richardson's ground squirrel and Swainson's hawk are precisely the same.[12]

Swainson's hawk will defend its breeding territory from other buteos. Breeding densities may vary from one area to the next but averages one pair per 2.5 sq mi (6.5 km2). The average home range estimate for this hawk is 1 to 2 sq mi (2.6 to 5.2 km2). It gathers in groups for feeding and migrating. However, in each case, such gathering is not social, but motivated by good feeding or migrating conditions.

Swainson's hawk, the red-tailed hawk (B. jamaicensis) and the ferruginous hawk (B. regalis) compete for territory, and defend territories against each other. In many parts of the plains these three species nest in the same general area and exploit much the same prey base. Although diets overlap greatly, habitats may not overlap as much. In Oregon, Swainson's hawk selects nesting trees having a different configuration than those used by red-tailed or ferruginous hawks. In southern Alberta, different nesting habitats help reduce food competition, with Swainson's hawk favoring areas with scattered trees or riparian borders, while red-tailed hawks nest in stands of tall trees, and ferruginous hawks nest on the open plains.

Reduced reproductive success may result from Swainson's hawk's nesting proximity to these two other buteos. Swainson's hawk is generally tolerant of people. The bird is attracted to haying, mowing, and plowing operations. House sparrows, European starlings, and other small birds may nest in or near a Swainson's hawk's nest.

In winter quarters, they are far more tolerant, though many birds will still fend for themselves. In Uruguay, the species likes largely open but broken (with rocks or woods) plains or low hills, where it can be seen to gather in larger groups. Groups of a few dozen birds are not uncommon. Flocks of over one hundred birds have been recorded several times, e.g. one that roamed the Cuchilla Marincho region south of Andresito (Flores Department) in mid-late December 2005.[11]

Natal Dispersal

Swainson’s hawks have a high natal fidelity, and individuals generally return to areas where they fledged. On average, female natal dispersal (mean distance of 11.1 kilometers) was higher than males (mean distance of 8.3 kilometers) in northern California. Longer natal dispersal distance in females is typical for many bird species, and may aid in inbreeding avoidance. Natal dispersal in the Canadian prairies was significantly higher at 66.7 kilometers, with documented movements as far as 310 kilometers.

Males that fledged in territories with higher primary productivity had lower natal dispersal in northern California, suggesting they were trying to stay closer to more prey-dense habitat.[13]

Hunting and food

Swainson's hawks hunt using various methods. Many still-hunt, watching for prey activity from a perch such as a tree, bush, pylon, telephone pole, hummock or other high object.[3] Others hunt by soaring over open ground with wings held in a dihedral, using their stellar vision to watch for prey activity below. It occasionally courses low over the ground like a northern harrier (Circus cyaneus) or hovers like a rough-legged hawk (B. lagopus) while hunting. They frequently engage in transect-glides while actively hunting in flight.[3] It commonly perches on the ground both during migration and on the breeding grounds. While hunting on the ground, almost entirely for large insects, their gait can appear awkward but they are often successful in pinning down several insects per day.[3] During migration, it typically roosts for the night on bare ground with scattered trees, a habit that distinguishes it from fellow long-distance migrants such as the broad-winged hawk (B. platypterus), which roosts in closed-canopy woodlands.

These birds patrol open areas or scan for prey from a perch; they may also catch insects in flight. They take advantage of insects turned up by farm equipment or driven out by fire. A hunting Swainson's hawk will use several strategies. It hunts insects such as dragonflies or dobsonflies while in flight, flapping little as it rides a wind current and stoops upon a fly, grabbing it with its foot and immediately transferring the prey to its bill. It uses a similar strategy to grab individual free-tailed bats from flying streams of bats. Also, when dragonfly hordes are grounded by weather, Swainson's hawk will stand near groups sheltering from the wind and pluck at individual insects. Swainson's hawk closely follows both tractors and wild fires for injured or fleeing food. It will also run down insect prey on the ground. Occasionally a hawk will stand still on a dirt bank or elevated mound waiting for prey to appear. It commonly hunts from elevated perches such as telephone poles, stooping on prey when it is sighted.

Grasshopper, a favorite food of Swainson's hawk

Swainson's hawks may be largely insectivorous except when nesting. Insect prey commonly taken includes grasshoppers, crickets, and locusts. Other Buteo hawks in this species range, including smaller-bodied species, do not normally prefer insects in their diet but instead focus on rodents and other small vertebrates.[3] However, breeding birds switch mainly to capturing vertebrate prey, which pairs then bring to their nestlings. Breeding Swainson's hawks rely heavily upon small mammals such as young ground squirrels, young cottontails, pocket gophers, mice, young jackrabbits, and, at least locally, small birds and other vertebrates including reptiles and amphibians. Birds taken include large birds such as Mallards, and Sage Grouse which may have been injured initially.

Other unusual bird species taken include American kestrel, and young short-eared owls. More typical in size are young lark buntings taken at their fledging time. Reptiles, which can comprise large parts of a diet, include snakes such as racers, gopher snakes and striped whipsnakes, and lizards. Amphibians may include tiger salamanders and toads. Swainson's hawk is an opportunistic feeder which responds quickly to local concentrations of food.

In Argentina, flocks of immature Swainson's hawks feed on flocks of the migratory darner dragonfly Rhionaeschna bonariensis, following the hordes of insects and feeding mostly on the wing. Local outbreaks of locusts may also be exploited for food by one or more age-classes of birds. The immatures wintering in southern Florida apparently feed upon either insects, mice, or both, when turned up from field plowing. They move from one freshly ploughed field to the next.

There is also some evidence that road-killed birds and animals are also consumed both on the wintering grounds and on the breeding grounds. The species commonly follows tractors and other agricultural equipment during haying or ploughing, where rodents are exposed for the hawks to capture, or insects are uncovered after crop cutting. Wildfires often attract foraging Swainson's hawks, especially grass fires in their South American wintering range. In South American grass fires, the hawks frequently wait around the edges of the fire, picking off not only insects but also vertebrates including nothuras, lizards and snakes.[3]

Reproduction

A Swainson's hawk chick

When Swainson's hawks arrive at their nesting sites in March or April, they may return to their original nests as these hawks are noted to be monogamous. Research indicates that they have a high degree of mate and territorial fidelity. This is unusual in a long-distance migrant. Seven to fifteen days after the birds arrive, the males begin constructing nests on the ground, ledges or in a trees. The nest consists of twigs and grasses and can take up to two weeks to complete. New nests may be constructed, old nests refurbished, or abandoned nests of other species — namely corvids (e.g. common raven, black-billed magpie, and American crow) — are refurbished.

The courtship displays of Swainson's hawk are not well known. One activity involves circling and diving above a potential nest site. The underwings and rump are flashed and the birds call. The display may end with one bird diving to land on the edge of the nest. Copulation occurs mainly in the morning and evening on the dead limbs of trees. The female may assume the receptive position without a prior display. During treading one of the birds calls.

Swainson's hawks typically nest in isolated trees or bushes, shelterbelts, riparian groves, or around abandoned homesteads. Occasionally, a pair will nest on the ground or on a bank or ledge. Nest trees and bushes include ponderosa pine, Douglas-fir, spruce, cottonwood, domestic poplar, aspen, elm, mesquite, willow, saguaro cactus, and soaptree yuccas. Nests are located from 9 to 15 ft (2.7 to 4.6 m) above the ground, often in the shaded canopy but near the top of the tree. Nests are flimsy structures, usually smaller than the nests of the red-tailed hawk, and often blow down after nesting season.

Juvenile Swainson's hawk

Clutch size ranges from one to four eggs, but averages two to three. Each egg is elliptical in shape, about 2.25 in (57 mm) long and 1.8 in (46 mm) wide. The egg is smooth with fine granulations and the ground color is white, often tinted bluish or greenish. During incubation the shell color quickly wears to dull white. Some eggs are plain; others are lightly marked with spots and blotches of light brown. The incubation period is 34 to 35 days, with the female incubating while the male brings food.

Young Swainson's hawks are fed small, young mammals. Flight feathers begin to emerge on the young at 9 to 11 days. High nestling mortality often occurs when the young are 15 to 30 days old and may be a result of fratricide. The young begin to leave the nest for surrounding branches at 33 to 37 days, fledging occurs at about 38 to 46 days. The fledglings are dependent upon their parents for 4 to 5 weeks. This species has one brood a year and apparently does not lay replacement clutches.

Lifespan

The oldest wild Swainson's hawk on record is 26 years 1 month (Swainson's Hawk26 years 01 months07/06/1986CaliforniaLocalUnknown07/24/2012CaliforniaSaw or photographed neck collar, color band, or other marker (not federal band) while bird was freeAlive - Released/Left On Bird). There are a number of cases of Swainson’s hawks living over 20 years old.[14] In the Canadian prairies, researchers found one 17 year old Swainson’s hawk still alive and breeding.[15] In northern California, several individuals banded as nestlings reached at least 20 years old in this population, though the age distribution suggests that these individuals are rare in a breeding population. In contrast to these relatively old individuals, most individuals that survived to breeding age in northern California died at 9.2 ± 5.5 years old, and there were not differences in longevity between males and females.[16]

Swainson's hawks die because of collisions with traffic, illegal shooting, electrocution, and even during severe prairie weather such as hailstorms. Wind storms and hail caused 30% nest failure in one study. When sharing a grove with nesting great horned owls, the hawks suffer much egg loss due to owl predation. The species also suffers from frequent, unexplained egg infertility.

Status and conservation

Injured light-morph Swainson's hawk recuperating in Boise Zoo

Swainson's hawk has suffered population declines since the first half of the twentieth century and was Blue-listed in the United States from 1972 to 1982. It has since been placed on the National Audubon's List of Special Concern in 1986. It is now listed by the United States Fish and Wildlife Service as a Category 3C candidate. Swainson's hawk was removed from the active federal list because it was found to be more abundant than previously thought; it is not considered a threatened species by the IUCN.[1] It remains listed as a threatened species by the California Department of Fish and Game as it has been since 1983.

A major cause of Swainson's hawk population decline was pesticide use in its wintering grounds of Argentina. Farmers there were using pesticides (DDT and monocrotophos) to control grasshopper and locust infestations, and Swainson's hawks were ingesting these pesticides in several different ways, but mainly by gorging themselves on the insects as they lay dying. The U.S. has worked with Argentine farmers to resolve this problem.[17]

Swainson's hawk has adapted well to grazing and pastureland and seems to be holding its own over much of its breeding range, from northern Mexico to the southern parts of the prairie provinces. However, far western populations, like that of Oregon, and southern California, have drastically declined, often due to habitat loss or incompatible agricultural practices. A possible reason for declines in parts of its range may be agriculturally motivated reductions in populations of both ground squirrels and grasshoppers, major seasonal foods.

Although often nesting close to human activity, some Swainson's hawks are very easily disturbed at the nest and often desert, especially early in the season. The bird is often quite tame and an easy target for shooters traveling isolated prairie roads. The species may also be affected in ways yet to be understood by some insecticides and herbicides, including those used on its wintering grounds.[17]

Observing Swainson's hawk

One of the best places to view the hawk is in the Snake River Birds of Prey National Conservation Area (NCA) in Idaho. Birds in the NCA are most frequently sighted in mid March, May, and June, in the early morning and evening when they are actively hunting. In April, Swanson's hawks engage in more sedentary breeding and egg-guarding, and are thus more difficult to spot. In July, rising canyon temperatures make prey scarce, so many birds of prey migrate away.

References

This article incorporates text from the Bureau of Land Management which is in the public domain.
  1. ^ a b c BirdLife International (2016). "Buteo swainsoni". IUCN Red List of Threatened Species. 2016: e.T22695903A93533217. doi:10.2305/IUCN.UK.2016-3.RLTS.T22695903A93533217.en. Retrieved 12 November 2021.
  2. ^ Bollmer, Jennifer L.; Kimball, Rebecca T.; Whiteman, Noah Kerness; Sarasola, José Hernán; Parker, Patricia G. (2005). "Phylogeography of the Galápagos hawk (Buteo galapagoensis): A recent arrival to the Galápagos Islands". Molecular Phylogenetics and Evolution. 39 (1): 237–247. doi:10.1016/j.ympev.2005.11.014. PMID 16376110 – via ResearchGate.
  3. ^ a b c d e f g h i Ferguson-Lees, J.; Christie, D. (2001). Raptors of the World. London: Christopher Helm. pp. 717–719. ISBN 0-7136-8026-1.
  4. ^ Goldstein, Michael I.; Bloom, Peter H.; Sarasola, Jose H.; Lacher, Thomas E. (1999). "Post-Migration Weight Gain of Swainson's Hawks in Argentina". Wilson Bulletin. 111 (3): 428–432. JSTOR 4164111.
  5. ^ "Swainson's Hawk". All About Birds. Cornell Lab of Ornithology. Retrieved 3 March 2013.
  6. ^ Sibley, David Allen (2000). The Sibley Guide to Birds. New York: Alfred A. Knopf. p. 120. ISBN 0-679-45122-6.
  7. ^ Kochert, Michael N.; Fuller, Mark R.; Schueck, Linda S.; Bond, Laura; Bechard, Marc J.; Woodbridge, Brian; Holroyd, Geoff L.; Martell, Mark S.; Banasch, Ursula (2011-02-01). "Migration Patterns, use of Stopover Areas, and Austral Summer Movements of Swainson's HawksPatrones de Migración, Uso de Áreas de Parada y Movimientos durante el Verano Austral en Buteo swainsoni". The Condor. 113 (1): 89–106. doi:10.1525/cond.2011.090243. ISSN 0010-5422. PMC 4570029. PMID 26380528.
  8. ^ Airola, Daniel A.; Estep, James A.; Krolick, David E.; Anderson, Richard L.; Peters, Jason R. (August 2019). "Wintering Areas and Migration Characteristics of Swainson's Hawks That Breed in the Central Valley of California". Journal of Raptor Research. 53 (3): 237–252. doi:10.3356/JRR-18-49. ISSN 0892-1016.
  9. ^ Laverde-R., Oscar; Stiles, F. Gary; Múnera-R., Claudia (2005). "Nuevos registros e inventario de la avifauna de la Serranía de las Quinchas, un área importante para la conservación de las aves (AICA) en Colombia" [New records and updated inventory of the avifauna of the Serranía de las Quinchas, an important bird area (IBA) in Colombia] (PDF). Caldasia (in Spanish). 27 (2): 247–265.
  10. ^ Olmos, Fábio; Pacheco, José Fernando; Silveira, Luís Fábio (2006). "Notas sobre aves de rapina (Cathartidae, Acciptridae e Falconidae) brasileiras" [Notes on Brazilian birds of prey] (PDF). Revista Brasileira de Ornitologia (in Portuguese). 14 (4): 401–404. Archived from the original (PDF) on 2008-12-17.
  11. ^ a b Azpiroz, Adrián B.; Menéndez, José L. (2008). "Three new species and novel distributional data for birds in Uruguay". Bulletin of the British Ornithologists' Club. 128 (1): 38–56.
  12. ^ Schmutz, Josef K.; Hungle, Daniel J. (2011-02-14). "Populations of ferruginous and Swainson's hawks increase in synchrony with ground squirrels". Canadian Journal of Zoology. 67 (10): 2596–2601. doi:10.1139/z89-366.
  13. ^ Briggs, Christopher W.; Collopy, Michael W.; Woodbridge, Brian (2012-11-01). "Correlates and Fitness Consequences of Natal Dispersal in Swainson's HawksCorrelatos y Consecuencias en la Adecuación Biológica de la Dispersión Natal en Buteo swainsoni". The Condor. 114 (4): 764–770. doi:10.1525/cond.2012.120034. ISSN 0010-5422. S2CID 84490400.
  14. ^ Bird Banding Lab (2021-02-22). "Bird Banding Lab Longevity Records".{{cite web}}: CS1 maint: url-status (link)
  15. ^ Houston, C. Stuart (2005-03-01). "Swainson's hawk longevity, colour banding and natal dispersal". Blue Jay. 63 (1). doi:10.29173/bluejay5854. ISSN 2562-5667.
  16. ^ Kane, Sarah A.; Vennum, Christopher R.; Woodbridge, Brian; Collopy, Michael W.; Bloom, Peter H.; Briggs, Christopher W. (2020-07-01). "Age distribution and longevity in a breeding population of Swainson's Hawks, Buteo swainsoni". Journal of Ornithology. 161 (3): 885–891. doi:10.1007/s10336-020-01776-7. ISSN 2193-7206. S2CID 216085596.
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Swainson's hawk: Brief Summary

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Swainson's hawk (Buteo swainsoni) is a large bird species in the Accipitriformes order. This species was named after William Swainson, a British naturalist. It is colloquially known as the grasshopper hawk or locust hawk, as it is very fond of Acrididae (locusts and grasshoppers) and will voraciously eat these insects whenever they are available.

Their breeding habitat is prairie and dry grasslands in western North America. They build a stick nest in a tree or shrub or on a cliff edge. This species is a long-distance migrant, wintering in Argentina; it has been recorded as a vagrant in neighboring Chile, in the island countries of the Dominican Republic, and Trinidad and Tobago, and in Norway.

This species or its immediate predecessor is the ancestor of the Galápagos hawk, as demonstrated by recent research. Then later diverged from the mainland birds perhaps 300,000 years ago, a very short time in evolution.

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