The Swainson’s Hawk (Buteo
swainsoni ) is a common bird in the western plains of North
America. It is a medium-sized hawk with a stout body, broad
wingers, and a rounded tail. The adult Swainson's hawk has dark
brown plumage with a brown breast and a pale belly. It also has a
conspicuous white patch on its throat.
Swainson’s
Hawks are also known as "grasshopper hawks" due to the large numbers
of grasshoppers they eat. A Swainson’s Hawk will fly behind tractors
and snatch any small animals or insects that are disturbed as the
tractor goes by. Pellet analysis has shown that a single hawk can
consume an average of 100 grasshoppers each day.
As a soaring,
open-country hunter, it often hunts from perches such as tree tops,
poles or posts, rocks, and elevated ground, surprising prey like
ground squirrels, pocket gophers, voles, deer mice, various small
birds, lizards and snakes.
As the summer
gives way to autumn, Swainson’s Hawks begin to put on fat for their
upcoming journey by gorging on grasshoppers until northerly winds
arrive and the flocks begin their migration south. Nearly the entire
population of Swainson's Hawks migrates from the temperate zone of
North America to its wintering grounds in the pampas of South
America. They migrate in great flocks – called kettles – that
contain thousands of birds. Because these raptors ride thermals
for most of their flights, they must stay close to the land where
thermals are common. For a few days each fall, virtually the entire
population of Swainson’s hawks darkens the skies above Panama, as
they follow the curve of the land along the narrowest point between
North and South America.
The 12,000 mile
roundtrip that this hawk travels each year places it among the
world's longest-distance migratory raptors. A Swainson's Hawk can
make the 6,000 mile trip in less than two months, averaging nearly
125 miles per day. A study of the migration route of Idaho’s
Swainson’s Hawks was conducted by the Raptor Research Center at
Boise State University. To see the results of this study, go to
http://rrc.boisestate.edu/Past%20Projects/Per%20Fal%20and%20Swai%20Hawk/peregrine_falcon_and_swainson.htm
Today,
Swainson’s hawks are in decline because of habitat loss and
pesticide use, which affects the birds directly and also eliminates
many of the insects that they rely on during the winter.
