Selected Birds of the Boreal Forest of North America



Broad-winged Hawk, adult
© Ron Austing



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Arrows represent general migration routes.
The arrows do not necessarily link specific
breeding and wintering grounds.
Broad-winged Hawk
Buteo platypterus

Shy and inconspicuous on its forested breeding grounds, the Broad-winged Hawk migrates in flocks that fill the skies, providing one of the greatest wildlife spectacles on the planet.  In many parts of its tropical wintering grounds it is the most abundant raptor.  Despite these facts, many aspects of its ecology remain poorly understood.

Habitat:
The Broad-winged Hawk is essentially a forest and woodland species throughout its range and at all times of year.  Only pure coniferous forests are avoided.  Small canopy openings, which it uses for foraging, are an important habitat component, and it often shows a preference for undisturbed, relatively young stands near water.  It may roost in arid tropical scrub during migration.  Winter habitat may include plantations if sufficient prey is present.

Diet/Feeding Behavior:
The Broad-winged Hawk is primarily a predator of small mammals and amphibians but will eat reptiles, birds, and various invertebrates opportunistically.  Prey consumption tends to reflect availability.  The prominence of frogs in its diet likely explains its association with water and perhaps even its migration schedule.  It is a sit-and-wait, "sentinel" predator, spending much time scanning quietly for prey from perches and then swooping on it in a manner described as "catlike."  Prey is sometimes taken on the wing; dragonflies and butterflies captured in this manner likely represent a significant portion of the diet during migration.  Prey is usually eaten immediately, but caching has been reported and may in fact be common.

Breeding:
The breeding biology of this species is typical of the family Accipitridae.  Pair formation occurs soon after arrival on the breeding grounds (mid-April to early June, depending on latitude) and includes courtship flights called "high circling," "sky-dancing," and "tumbling."  The nest is a small, loose twig structure about 6 to 30 meters (18-90 ft) high, built by both birds over a period of several weeks.  Two or three (rarely four) speckled and blotched white eggs are laid and incubated  for 28 to 31 days.  The young are brooded by the female while the male provides food for a week or two, after which both parents hunt.  The nestlings fledge at 29 to 30 days and start hunting a week or two later but remain dependent on the adults until seven to eight weeks of age.

Migration/Winter Range:
The fall migration of the Broad-winged Hawk is perhaps the best-known and most spectacular aspect of its ecology.  Departing the breeding grounds ahead of most other raptors, perhaps forced to do so by scarcity of amphibian prey, it forms large flocks known as "kettles" that often number in the tens of thousands and include other raptor species.  Often using thermals, most Broad-wings pass over a given area within a two-week period, though the first and last birds may be two months apart.  Fall migration routes are generally somewhat east of spring routes.  Most of the population passes along the Great Lakes, Appalachians, and Mississippi Valley, with smaller numbers following western mountain ranges and the Pacific coast.  Long-distance water crossings are avoided.  Flyways converge in south Texas, then follow the Gulf of Mexico coastline south.  The winter range extends from southern Mexico to northern Argentina, with a small population wintering in south Florida and resident populations in the West Indies, where five of the six subspecies occur.  Spring migration is more solitary, with few large concentrations reported outside south Texas and the southern shores of the Great Lakes; and is later than that of most raptors, again probably reflecting availability of amphibian prey.

Conservation Issues and Status:
Though still common in most areas, the Broad-winged Hawk does seem to be declining  widely. Due to the species' secretive nature when nesting, the Breeding Bird Survey (BBS) does not sample it particularly well; nevertheless, it shows an overall decline of nearly 2 percent annually from 1980 to 2002 after a strong increase from 1966 to 1979.  Significant recent BBS trends are displayed in Wisconsin, Quebec, Tennessee, and Alabama (all negative); and Arkansas and Florida (positive).  Eastern migration counts show a decline in the 1990s after decades of growth, but these could be the result of shifts in migration patterns.  Declines, if actual, may be  the result of forest fragmentation or declines in amphibian populations; ironically, the species' use of amphibians for food may have spared it from earlier, DDT-related problems that decimated bird-, fish-, and insect-eating species.  Western migration counts have been increasing, suggesting that the species is expanding its breeding range westward in Canada, probably owing to the creation of canopy gaps and edges by logging.  No trends are evident from Christmas Bird Count results.  Shooting, pesticides, and deforestation remain significant potential threats to this species in Latin America; Caribbean populations are threatened by forest clearance for agriculture.


References:

Fitch, H. S.  1974.  Observations of the food and nesting of the Broad-winged Hawk (Buteo platypterus) in northeastern Kansas.  Condor 76:331-360.

Goodrich, L. J., S. C. Crocoll, and S. E. Senner.  1996.  Broad-winged Hawk (Buteo platypterus).  In The Birds of North America, No. 218 (A. Poole and F. Gill, Eds.).  Philadelphia: The Academy of Natural Sciences; Washington, D.C.: The American Ornithologists' Union.

Matray, P. F.  1974.  Broad-winged Hawk nesting and ecology.  Auk 91:307-324.

National Audubon Society.  2002.  The Christmas Bird Count Historical Results [Online].  http://www.audubon.org/bird/cbc.

Rosenfield, R. N.  1984.  Nesting biology of Broad-winged Hawks in Wisconsin.  Raptor Res. 18:6-9.

Rusch, D. H., and P. D. Doerr.  1972.  Broad-winged Hawk nesting and food habits.  Auk 89:139-145.

Sauer, J. R., J. E. Hines, and J. Fallon.  2003.  The North American Breeding Bird Survey, Results and Analysis 1966-2002, Version 2003.1, USGS Patuxent Wildlife Research Center, Laurel, MD.

Birding content provided by National Wildlife Federation/eNature with support from Ducks Unlimited/The Pew Charitable Trusts

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