The Swainson’s hawk is similar in size to the Red-tailed hawk, a bit shorter in length at 17-22 inches, but with a wider wingspan of 4-4.5 feet. Males average about 29 ounces. This hawk breeds throughout the prairies and farmlands of the Great Plains, from Central Texas west to Central Arizona and up north into the Southern Canadian prairies of Alberta and Saskatchewan. Scattered trees in its preferred habitat provide nesting sites. It is a long-distance migrant, flying to Argentina for the winter, and covering up to 7,000 miles in about two months. They are energy efficient travelers, gaining altitude in thermals and then gliding long distances with a trailing wind, looking for the next thermal.
Swainson’s hawks have two color morphs, the light morph accounting for about 90% of birds and the less common darker bird is found in far western populations. In New Mexico I have seen the dark morph occasionally, possibly in about one out of 10 observations. The light morph has a gray head and brown to rusty patch on the front of the breast. The belly is white to lightly speckled with brown. The white of the belly feathers extends out into the underside of the leading edge primaries, with the wing’s trailing edge being dark brown to black. This pattern of a white leading edge and dark trailing edge as seen from underneath is a very distinct identifying characteristic of Swainson’s hawks in flight.
The dark morph has a solid dark gray head, neck and breast, with lighter brown to rusty colored belly. This light orange color of the belly extends out onto the leading edge primaries with a broad dark band across the trailing edge and outer wing feathers.
These hawks prey on small mammals, reptiles, and other vertebrates early in the breeding season and also feed these animals to their nestlings. The female will brood the eggs for about a month, with the male supplying food to his mate. Nestlings fledge after about six weeks and may stay with the parents until the fall migration.
Swainson’s hawks will also take small birds, bats, and even carrion. Their breeding range overlaps with Red-tail and Ferruginous hawks. Competition for limited nesting sites is reduced by microhabitat preferences among the three species. Swainson’s hawks prefer scattered trees for nesting amid grasslands or riparian borders. Red-tails nest in denser stands of mature trees, and Ferruginous hawks will tend to find nesting sites in more open plains habitat. Nest site competition can also occur with Great horned owls, which also select trees scattered over open prairies for nesting. The defended territory and hunting range of Swainson’s hawks may cover two square miles.
After the nestlings are grown Swainson’s hawks will concentrate on a diet of insects, a habit that sometimes earns them a common name of grasshopper or locust hawks. They will catch flying insects in the air or chase them around on the ground. They are often seen standing on the surface where they hunt for grasshoppers and caterpillars. And they will follow after agricultural equipment, catching grasshoppers as they are flushed out of the vegetation.
Banding records have revealed several individuals living past 20 years, with the oldest on record reaching over 26 years old. However, research has indicated that average life expectancy is in the range of 9-10 years. Mortality factors include vehicle collisions, illegal hunting, electrocution, and prairie hail storms. I have witnessed large storms on the prairies of South Dakota that produce large hail in enormous volumes in an exposed grassland environment, where birds could have easily fallen victim. One study found 30% nest failure due to hail damage to eggs and nestlings.
Swainson’s hawk populations are thought to be experiencing a general decline over the last century. Use of DDT and other pesticides by farmers in Argentina to control locust and grasshopper populations have impacted wintering hawk populations there. The hawks accumulate the organotoxins in their bodies as they gorge on the dying insects on the ground.
The IUCN lists the Swainson’s hawk as a species in the category of “least concern” due to overall abundance and population stability. However, in California the most 2016 report of the Department of Fish and Game recommended continuation of the threatened population status there due to habitat losses and other factors detrimental to the hawks.
The Audubon Society predicts that Swainson’s hawks may see an increase in breeding range along the eastern portion of their Great Plains distribution as climate warming proceeds. Some losses are expected in the southern portions of the breeding range in Texas and Mexico.
Photos taken with the Nikon P900 camera by James Taulman.