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BC Conservation Data Centre: Species Summary


Buteo swainsoni
Swainson's Hawk


 
Scientific Name: Buteo swainsoni Bonaparte, 1838
English Name: Swainson's Hawk
 
Classification / Taxonomy
Scientific Name - Concept Reference: American Ornithologists' Union (AOU). 1998. Check-list of North American birds. Seventh edition. American Ornithologists' Union, Washington, D.C. [as modified by subsequent supplements and corrections published in The Auk]. Also available online: http://www.aou.org/.
Classification Level: Species
Species Group: Vertebrate Animal
Species Code: B-SWHA
Kingdom Phylum Class Order Family
Animalia Craniata Aves Accipitriformes Accipitridae
   
Conservation Status / Legal Designation
Global Status: G5 (Apr 2016)
Provincial Status: S2B (Mar 2022)
BC List: Red
Provincial FRPA list:   
Provincial Wildlife Act:
COSEWIC Status:
SARA Schedule:
General Status Canada: 4 - Secure (2005)
Migratory Bird Convention Act:
   
Ecology & Life History
General Description:
Global Reproduction Comments: Egg dates: mainly April-May in southwestern U.S., California, and Oregon; mainly May-June in central plains states and Canada. Clutch size usually is 2-3. Incubation lasts 34-35 days per egg, almost exclusively by female (male provides food). Young are tended by both adults, leave nest in about 30 days, attain flight at 42-44 days (around 3rd week in July in southwestern U.S.), dependent on parents for 4-4.5 weeks after fledging. First breeds at 2 years. Usually 0.1-0.2 pairs per sq km; average of 1.4-2.4 km between nests. See Bednarz (1988) for information on reproduction in New Mexico. Reported nest density throughout range varies from 0.08-1.61 nests per sq km.
Global Ecology Comments: May form premigratory aggregations in summer. Nesting density in suitable habitat varies throughout range from 0.1-1.6 nests per 10 sq km (Bednarz and Hoffman 1988); nests average 1.4-2.4 km apart (see Rothfels and Lein 1983). At one site in California, five nests typically found along a 1 km riparian strip, the nearest nests only 60 meters apart (England et al. 1997). Home ranges during breeding season vary greatly--from 69 to 8718 hectares (reviewed in England et al. 1997). Interspecific territoriality with Red-tailed Hawk in some areas; in other areas may compete with Ferruginous Hawk or be limited by presence of and predation by Great Horned Owl (Palmer 1988).

In California, dispersal distances from natal sites to subsequent breeding sites ranged from 0 to 18 kilometers, mean 8.8 kilometers (Woodbridge et al. 1995). In contrast, none of 697 banded nestlings in Saskatchewan returned to the study area; three were found 190, 200 and 310 kilometers away (Houston and Schmutz 1995).
Migration Characteristics:
(Global / Provincial)		 
    Nonmigrant:
    Local Migrant:
    Distant Migrant:
    Within Borders Migrant: 		N /
N /
Y /
na /
Global Migration Comments: In migration, occurs regularly in most of Middle America, and rarely east along the Gulf Coast to Florida (AOU 1983). In California, migrates March-early May, with a peak in the first half of April, and September-October (Biosystems Analysis, Inc. 1989). Migrants are greatly concentrated as they pass through Panama (mostly March-early April and October-early November; Ridgely and Gwynne 1989). Migrates through Costa Rica late September-November and late February-early May (Stiles and Skutch 1989). In Colombia, flocks of various sizes reported mainly February-March and September-early November (Hilty and Brown 1986). Main northward migration passes through Panama in mid-March, Veracruz in latter half of March and early April, southern Texas and southwstern U.S. chiefly in April (Palmer 1988); fall concentrations and movements occur in August-September in the north, mainly early October in Texas; peak in migration occurs in September in the southwestern U.S.; arrives in Argentina in late November (Palmer 1988). Annual migration flight may be 18,000-27,000 km, encompasses 4 months of the year. See Houston (1990) for information on migrations of Saskatchewan breeders. Migrates in large, often immense, flocks. Migrates over terrain where updrafts provide needed buoyancy for soaring. May roost at night on ground during migration.
Habitats:
(Type / Subtype / Dependence) 		Agriculture / Cultivated Field / Facultative - frequent use
Agriculture / Hedgerow / Facultative - frequent use
Agriculture / Pasture/Old Field / Facultative - frequent use
Alpine/Tundra / Alpine Grassland / Unknown
Anthropogenic / Industrial / Facultative - occasional use
Anthropogenic / Urban/Suburban / Facultative - occasional use
Forest / Conifer Forest - Dry / Facultative - occasional use
Forest / Conifer Forest - Mesic (average) / Facultative - occasional use
Forest / Deciduous/Broadleaf Forest / Facultative - frequent use
Forest / Mixed Forest (deciduous/coniferous mix) / Facultative - occasional use
Grassland/Shrub / Antelope-brush Steppe / Facultative - frequent use
Grassland/Shrub / Grassland / Facultative - frequent use
Grassland/Shrub / Meadow / Facultative - frequent use
Grassland/Shrub / Sagebrush Steppe / Facultative - frequent use
Riparian / Riparian Forest / Facultative - occasional use
Riparian / Riparian Shrub / Facultative - occasional use
Global Habitat Comments: Savanna, open pine-oak woodland and cultivated lands (e.g., alfalfa and other hay crops, and certain grain and row croplands) with scattered trees. Tolerates extensive cultivation in nesting area (Schmutz 1989), though vineyards, orchards, rice, corn, and cotton are not suitable foraging habitat. In migration and winter also in grasslands and other open country (AOU 1983). Migrants may roost at night on ground in very large fields (Ridgely and Gwynne 1989). Nests typically in solitary tree, bush, or small grove; many nests on old black-billed magpie nests; sometimes on rock ledge. Readily nests in trees in shelterbelts and similar situations produced by humans (Gilmer and Stewart 1984). Recently reported nesting in city trees and on railway signal gantry in Regina, Saskatchewan (Condor 94:773-774). In the Central Valley of California, nests often are within one mile of a riparian zone; Great Basin nests, usually in junipers, are not near riparian zones (Biosystems Analysis, Inc. 1989). Evidently often returns to area where it nested in previous year.

GREAT BASIN AND MOJAVE HABITAT:
Swainson's Hawks have adapted to agricultural landscapes in Nevada. An ideal landscape for the Swainson's Hawk provides large riparian nesting trees, agricultural fields, and open shrublands within relatively close proximity (GBBO 2010). Swainson's Hawks in the Great Basin occupy the Juniper/Sagebrush community typical to the area. In California, Swainson's hawk habitat generally consists of large, flat, open, undeveloped landscapes that include suitable grassland or agricultural foraging habitat and sparsely distributed trees for nesting (England et al. 1997). Populations in the Great Basin often use juniper trees (Juniperus sp.) for nesting (England et al. 1997), and at least three known nest sites in the Mojave Desert are in Joshua trees (Yucca brevifolia) (California Natural Diversity Database 2009) (PCCP 2010). In addition to Joshua trees, this species was also known historically from the Mojave Yukka (Yucca schidigera) and possibly desert riparian habitats (Bloom 1980).
Food Habits: Carnivore: Adult, Immature
Invertivore: Adult, Immature
Global Food Habits Comments: Vertebrates (mainly mammals) dominate the diet during the breeding season; invertebrates (especially crickets and grasshoppers) are common food at other times and sometimes for nonbreeders in summer. Hawks wintering in Argentina ate mainly dragonflies (Condor 95:475-479, Wilson Bull. 105:365-366). Mammals consumed often include young ground squirrels and pocket gophers. Depending on availability, also eats other small mammals, snakes, lizards, birds, amphibians, and some carrion (e.g., road kills). Hunts for insects on ground; may also catch insects in air. Hunts while soaring or from perch. Does not feed during most of migration (occasional feeding during initial and terminal stages) (Palmer 1988).
Global Phenology: Diurnal: Adult, Immature
Provincial Phenology:
(1st half of month/
2nd half of month)
Colonial Breeder: N
Length(cm)/width(cm)/Weight(g): 53/ / 1069
Elevation (m) (min / max): Global: 
Provincial: 
   
 
Distribution
Endemic: N
Global Range Comment: BREEDS: known to have bred in east-central Alaska east into Yukon Territory and extreme northwestern Mackenzie; central Alberta, central Saskatchewan, southern Manitoba, western and southern Minnesota, and western Illinois south (mainly east of Cascades and Sierra Nevada) to southern California (rarely), Baja California (formerly), Sonora, Durango, Chihuahua, central and southern Texas and western Missouri; eastern breeding limits unstable. WINTERS: according to AOU (1983), primarily on pampas of southern South America (south to Uruguay and Argentina), irregularly north to Costa Rica and Panama, casually or irregularly north to the southwestern U.S. (especially Texas) and southern Florida.
 
Authors / Contributors
Global Information Author: Hammerson, G.
Last Updated: Mar 30, 1995
Provincial Information Author:
Last Updated:
   
References and Related Literature
American Ornithologists' Union (AOU). 1983. Check-list of North American Birds, 6th edition. Allen Press, Inc., Lawrence, Kansas. 877 pp.
Bechard, M. J., R. L. Knight, D. G. Smith, and R. E. Fitzner. 1990. Nest sites and habitats of sympatric hawks (BUTEO spp.) in Washington. J. Field Ornithol. 61:159-170.
Bednarz, J. C. 1988a. Swainson's hawk. Pages 87-96 in Glinski et al., eds. Proc. Southwest Raptor Manage. Symp. and Workshop. Nat. Wildl. Fed. Sci. and Tech. Ser. No. 11.
Bednarz, J. C. 1988c. A comparative study of the breeding ecology of Harris' and Swainson's hawks in southeastern New Mexico. Condor 90:311-323.
Bednarz, J. C., and S. W. Hoffman. 1988. The status of breeding Swainson's hawks in southeastern New Mexico. Pages 253-259 in Glinski et al., eds. Proc. Southwest raptor management symposium and workshop. Nat. Wildl. Fed. Sci. and Tech. Ser. No. 11.
Biosystems Analysis, Inc. 1989. Endangered Species Alert Program Manual: Species Accounts and Procedures. Southern California Edison Environmental Affairs Division.
California Department of Fish and Game (CDF&G). 1990. 1989 annual report on the status of California's state listed threatened and endangered plants and animals. 188 pp.
Campbell, R.W., et al. 1988. Species Notes for Selected Birds, Vol. 2 in A.P. Harcombe, tech. ed. 1988. B.C. Minist. Environ., Lands and Parks, Wildl. Branch. Rep. R-16. 131pp.
Campbell, R.W., N.K. Dawe, I. McTaggart-Cowan, J.M. Cooper, G.W. Kaiser, and M.C.E. McNall. 1990b. The Birds of British Columbia Vol. 2: Nonpasserines: Diurnal Birds of Prey through Woodpeckers. Royal British Columbia Museum, Victoria, BC.
Cooper, J.M. 1998. An Inventory Report on the Status of Diurnal Raptors (Ferruginous Hawk, Swainson's Hawk, Prairie Falcon, Peregrine Falcon) at Risk in the Southern Grasslands of British Columbia. B.C. Minist. Environ., Lands and Parks, Wildl. Branch. Working Rep. WR-92. 24pp.
Demarchi, M.W. and M.D. Bently. 2005. Best Management Practices for Raptor Conservation during Urban and Rural Land Development in British Columbia. B.C. Minist. of Environ., Victoria, B.C. MoE BMP Series.
Dodd, N. L. 1988d. Fire management and southwestern raptors. Pages 341-347 in Glinski et al., eds. Proc. Southwest raptor management symposium and workshop. Nat. Wildl. Fed. Sci. and Tech. Ser. No. 11.
England, A. S., M. J. Bechard, and C. S. Houston. 1997. Swainson's Hawk (Buteo swainsoni). No. 265 IN A. Poole and F. Gill, editors, The birds of North America. The Academy of Natural Sciences, Philadelphia, PA, and The American Ornithologists' Union, Washington, DC. 28pp.
Fisher, A.K. 1893. The hawks and owls of the United States in their relation to agriculture. Washington U.S. Dept. of Agriculture Bull. no. 6. 210 pp.
Gilmer, D. S., and R. E. Stewart. 1984. Swainson's hawk nesting ecology in North Dakota. Condor 86:12-18.
Harrison, C. 1978. A Field Guide to the Nests, Eggs and Nestlings of North American Birds. Collins, Cleveland, Ohio.
Hilty, S.L. and W. L. Brown. 1986. A Guide to the Birds of Colombia. Princeton University Press, Princeton, USA. 836 pp.
Houston, C. S. 1990. Saskatchewan Swainson's hawks. Am. Birds 44:215-220.
Houston, C. S., and J. K. Schmutz. 1995. Swainson's Hawk banding in North America to 1992. North American Bird Bander 20:120-127.
Johnsgard, P. A. 1990. Hawks, eagles, and falcons of North America. Smithsonian Inst. Press, Washington, D.C. xvi + 403 pp.
Keast, A., and E.S. Morton. 1980. Migrant birds in the neotropics: ecology, distribution, and conservation. Smithsonian Institution Press, Washington, DC.
Kirk, D. A., and C. S. Houston. 1995. Productivity declines in Swainson's hawks and their significance to population trends. Bird Trends (Canadian Wildlife Service) (4):19-20.
Kirk, D. A., D. Hussell, and E. Dunn. 1995. Raptor population status and trends in Canada. Bird Trends (Canadian Wildlife Service) 4:2-9.
Palmer, R. S., ed. 1988b. Handbook of North American birds. Vol. 5. Yale Univ. Press, New Haven. 465 pp.
Pendleton, B. A. G., B. A. Millsap, K. W. Cline, and D. M. Bird. 1987. Raptor management techniques manual. National Wildlife Federation, Sci. and Tech. Ser. No. 10. 420 pp.
Ridgely, R. S., and J. A. Gwynne, Jr. 1989. A guide to the birds of Panama with Costa Rica, Nicaragua, and Honduras. Second edition. Princeton Univ. Press, Princeton, New Jersey. 534 pp.
Risebrough, R. W., et al. 1989. Investigations of the decline of Swainson's hawk populations in California. J. Raptor Res. 23:63-71.
Root, T. 1988. Atlas of wintering North American birds: An analysis of Christmas Bird Count data. University of Chicago Press. 336 pp.
Rothfels, M., and M. R. Lein. 1983. Territoriality in sympatric populations of Red-tailed and Swainson's hawks. Canadian Journal of Zoology 61:60-64.
Schmutz, J. K. 1989. Hawk occupancy of disturbed grasslands in relation to models of habitat selection. Condor 91:362-371.
Smith, N. G. 1980. Hawk and vulture migration in the Neotropics. Pages 51-65 in B80KEA02NAUS.
Stiles, F. G. and A. F. Skutch. 1989. A guide to the birds of Costa Rica. Cornell University Press, Ithaca, New York, USA. 511 pp.
Terres, J. K. 1980. The Audubon Society encyclopedia of North American birds. Alfred A. Knopf, New York.
Woodbridge, B., K. K. Finley, and P. H. Bloom. 1995. Reproductive performance, age structure, and natal dispersal of Swainson's Hawks in the Butte Valley, California. Journal of Raptor Research 29:187-192.
 

Please visit the website Conservation Status Ranks for definitions of the data fields used in this summary report.

Suggested Citation:

B.C. Conservation Data Centre. 1995. Species Summary: Buteo swainsoni. B.C. Minist. of Environment. Available: https://a100.gov.bc.ca/pub/eswp/ (accessed Mar 26, 2023).