Broad-winged Hawk (Buteo platyterus)

Distribution

Breeding: Widespread across southern Canada, extending from the Maritime provinces to Alberta; breeds east of the Great Plains in the United States, found south to the Gulf Coast, including northern Florida. “Dark” morphs (see “Description: Male” below) may be found in western and central Canada.

Winter: Southern Florida and from Mexico to South America.

Breeding habitat

Inhabits a variety of continuous forests, generally dry woodlands and mixed conifer-hardwoods with openings and water nearby.

Conservation status

Although this is one of the most common forest raptor species, it is of conservation importance because of its association with large tracts of mature forest both for breeding and wintering. Breeding populations are poorly monitored, but long-term trends appear to be stable, based on available data. Declines have been noted, however, since 1980 in New England, Quebec, and the southern Appalachians. Understanding this species’ sensitivity to forest fragmentation and various silvicultural practices will be important in maintaining healthy populations of Broad-winged Hawks.

Description

Male: Our smallest Buteo, wings are fairly pointed and tail is relatively short, occurs in two distinct morphs. Both “Light” and “Dark” birds have uniformly dark brown upperparts and pale underwings with a black border. “Light” birds show varying amounts of rufous streaks or bars on otherwise white breast and belly, and almost completely pale underwings. “Dark” birds, which are very uncommon (some estimates place “Dark” morphs at 1 in 50,000) show dark brown to almost black underparts; the leading edge of underwing is as dark as the breast and belly. Tail pattern in both morphs consists of wide, alternating dark and light bands.

Female: The plumage is the same as adult male. Although larger in size, overlap is considerable.

Juvenile: “Light” birds can be “lightly marked” or “heavily marked,” each showing variable amounts of brownish streaking and barring on white breast and belly. Lightly marked birds show almost completely pale underwings, while heavily marked birds show a patterned leading edge. Like “dark” adults, dark juveniles are completely dark underneath. Tail pattern in both morphs is similar, consisting of indistinct bands; juveniles all typically show a dark moustachial streak.

Vocalizations

Calls: The characteristic call is given throughout the year, including on the nest and in flight, and is described as a high-pitched whistle described as peeeurr, kee-eee, or peeoweeee, with the first note short and higher pitched than the second. Other calls include a “transfer,” a series of whines given by adults during food transfers; a “dismissal,” a more plaintive variation of the standard whistle given by female when male is approaching or leaving the nest; and a wheezy 2-tone whistle emitted on copulation, whee-ohh.

Foraging strategy

A sit and wait predator, described as “cat-like” perched on a limb within the forest. Swoops down to snatch prey from the forest floor. Adults appear to hunt more after mid-morning.

Diet

Diet depends on local availability of prey, but consists primarily of small mammals; also includes birds, amphibians, reptiles, and insects. Mammal prey is fully consumed, large snakes and frogs are skinned, birds are often plucked.

Behavior and displays

• Often soars in circles above the forest, probably as a territorial function; makes short flights from branch to branch within the forest

• Defends home range from conspecifics and Red-tailed Hawks.

Courtship

• Male and female call and respond during courtship, also performs flight displays, listed below.

• High Circling: an advertising display beginning immediately after arrival on breeding grounds. Birds are conspicuous and noisy, emitting peeeurr call. One bird, presumably male, side-slips or dives very close, to the other, presumably female.

• Sky-dancing: bird leaves perch, flapping upward in widening circles, calling. Then, with spread wings and tail, soars lightly back and forth, still going upward until nearly lost from sight. Finally descends with long sweeps and curves, terminating with long dash horizontal to the ground.

• Tumbling: a circling bird drops toward earth checking its headlong course just before reaching the ground.

• No information about courtship feeding.

Nesting

Nest Site: Usually located in the main crotch of deciduous tree, or on a platform of horizontal branches against the trunk of a conifer. Often placed in the upper third of the forest’s canopy and near water. Pairs may reuse their nest, or an old crow, hawk, or squirrel nest.

Height: Ranges from 20–90 feet (6–30 meters), but can be placed as low as 3–9 feet (1–3 meters) above the ground.

Nest: Sides of nest are built of fresh twigs and old dead sticks, fresh conifer sprigs are placed on nest rim or cup but are not incorporated into the nest itself. The cup is lined with bark chips, as well as corn husks, moss, inner tree bark, red cedar, wild grape vine, lichen, covered bark, chicken feathers, or pine needles.

Eggs: 2–3, rarely 4, white, pale creamy, or slightly bluish eggs marked in two layers of large patches to tiny dots.

Incubation period: Begins with the first egg and lasts from 28–31 days, solely by female.

Nestling period: Young are semi-altricial and downy at hatching; female broods almost continuously during first week. Males provide food, but only visit the nest after transferring food to female away from nest. Oldest nestling secures prey and feeds until sated, after which remaining nestlings feed. The young first leave nest at 29–31 days.

Fledgling period: Young leave nest at 5–6 weeks, but take first flight at about 31 days; flying skills develop rapidly. Fledglings observed using nest as feeding and roost site up to 2 weeks after first flight. After that, young stay on territory 4–8 weeks, intercepting parents to obtain prey at 6 weeks and beginning to capture prey about 7 weeks.

Broods: Single brooded.

Notes

• During favorable migration conditions large flocks, or “kettles,” are formed. Individuals soar to the top of thermals, and then glide to another to save energy during the long flight to the wintering area.

• Sensitive to tropical deforestation.