Buteo
swainsoni
(Swainson's Hawk)
Physical
Description:
19-22" (48-56 cm). Dark
brown above with reddish hood, white
throat and body accentuated by a dark bib-like band
across breast. Darker gray flight feathers highlight buffy
wing
linings. Indistinctly striped tail gray above often becoming white at the
base, light below with dark border. They are frequently found in dark morphs,
which don't have the white breast and belly. Also, th eleading edge of the wings
in both morphs is usually white, in contrast to that of Red-tails.
Similar Species- Red-tailed, Rough-legged, and Ferruginous hawks
Song:
Shrill, monotone skreeeeee,
also a shorter descending scream that trails off at the end.
Distribution:
Breeds in portions of Alaska
and western Canada, east to Minnesota and Illinois, and south to southern California,
parts of Mexico, Texas, and Missouri; eastern breeding limits are unstable,
Winters from southwestern U.S. and southeastern Florida (irregularly), south
to South America.
Diet:
Vertebrates (mainly mammals such as young
ground squirrels and pocket gophers) dominate diet during breeding season; invertebrates
(especially crickets and grasshoppers) are common food at other times. Depending
on availability, individuals also eat snakes, lizards, birds, amphibians, and
some carrion. Concentrations of Swainson's Hawks foraging on grasshoppers have
been documented in Idaho.
Ecology:
Hunts while soaring or from perch. Builds
stick nest in tree, or occasionally on cliff. nesting density in suitable habitat varies
from 0.1-1.6 nests/10 km2; nests average 1.4-2.4 km apart. May form pre- migratory
aggregations in summer and migrate in immense flocks
. Migrants may roost
at night on ground in
very large fields, and go without feeding during most of migration (with occasional
feeding during initial and terminal stages). In Idaho, species is highly migratory
(present between April and September and winters in Argentina). A 1985 survey
in southern Idaho located 109 occupied nests and indicated that Swainson's Hawks
were still a widespread common nester in state.
Conservation:
Element Code: | ABNKC19070 |
Status: | Protected nongame species |
Global Rank: | G4 |
State Rank: | S4,NTMB |
National Rank: | N5B |
Important
State References:
Bechard, M.J., K.D. Hague-Bechard, and
D.H. Porter. 1986. Historical and current distributions of Swainson's and Ferruginous
Hawks in southern Idaho. Dept. Biology, Boise St. Univ., Boise. 58pp.