An Animal of the High Desert - Swainson's Hawk

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.