Scientific name- “Buteo swainsoni.”
The Swainson’s hawk, also known as the grasshopper hawk or the locust hawk, is a medium-sized member of the Buteo hawk genus. These birds are summertime residents of western North America. However, in the fall, most of them migrate to eastern South America, as far south as the Pampas of Argentina, Uruguay, and Brazil, for the winter.
Swainson’s Hawk Characteristics
Swainson’s hawks are buteo hawks. As such, they are large, hefty birds. However, they are slimmer, and their wings are proportionately longer than some members of their genus.
For comparison, their average length is slightly shorter than that of Red-tailed hawks, yet they are 20% lighter. Their wings are longer than those of other buteo hawks and appear narrower in flight in proportion to their body size.
According to Cornell Bird lab, in size, Swainson’s hawks are 18.9-22.1 inches (48-56 cm) in length and 24.4-48.2 oz (693-1367 g) in weight. In size, they are sexually dimorphic, with females being 28% larger than males.
Swainson’s Hawk Range
Swainson’s hawks are almost 100% migratory. While they spend the spring and summer months on their breeding and nesting grounds in western North America, the vast majority of them migrate to South America for the winter.
During the fall migration, these birds head to South America in groups that may number in the hundreds or even thousands. Their migration flocks might even contain some Broad-winged hawks. Swainson’s hawks that nest in Northern Canada may travel over 7100 miles if they winter on the Pampas of Argentina.
The following Canadian provinces and territories have summertime breeding populations of Swainson’s hawks.
- Yukon Territory
- Northwest Territories
- British Columbia
- Alberta
- Saskatchewan
- Manitoba
The following U.S states have summertime breeding populations of Swainson’s hawks.
- east central Alaska
- Washington
- Oregon
- California
- Idaho
- Nevada
- Utah
- Arizona,
- Montana
- Wyoming
- Colorado
- New Mexico
- Texas
- North Dakota
- South Dakota
- Nebraska
- Kansas
- Oklahoma
- Minnesota
- Wisconsin
- Iowa
- Missouri
The following Mexican states have summertime breeding populations of Swainson’s hawks.
- Sonora
- Chihuahua
- Coahuila
- Sinaloa
- Nuevo Leon
The following countries have winter-time populations of Swainson’s hawks.
- Western Mexico
- El Salvador
- Honduras
- Nicaragua
- Panama
- Bolivia
- Uruguay
- Brazil
- Argentina
Swainson’s hawks end up in Chile, the Dominican Republic, and Trinidad and Tobago during the winter occasionally. However, these birds are considered to be vagrants or to be separated from their traditional range. Source
Swainson’s Hawk Habitat
These birds prefer the same type of habitat in the southern hemisphere that they do in the Northern hemisphere. That is chiefly wide-open grasslands, prairies, and deserts. This is the type of habitat it requires in both its breeding ranges and wintering ranges.
On their summer breeding and nesting ranges, they require an abundance of small mammals for prey to feed to their young. Consequently, their population correlates directly to their abundance or scarcity of them. For example, in Saskatchewan, the distribution and abundance of breeding Swainson’s hawk pairs correlate directly with the distribution and abundance of Richardson’s ground squirrels. Source
These birds have also adjusted to the fact that some of their range has been transformed into agricultural fields. Like Red-tailed hawks, they have learned to follow the farm machinery around during hay harvesting time. As the hay is harvested, their prey animals become exposed.
When Swainson’s hawks go to their winter range, they no longer rely on small mammals as their number 1 prey item. They primarily feed on large insects when they go to central and South America. This is how they’ve earned the appellation of grasshopper hawk. In South America, they consume a lot of grasshoppers.
Swainson’s Hawk Diet
Spring and Summer
During the breeding season and nesting season, Swainson’s hawks mainly prey on small mammals. The list of small mammals they prey on includes ground squirrels, prairie dogs, cottontail rabbits, jackrabbits, bats, mice, and voles.
They also feed on reptiles such as snakes and lizards. Birds are also an item on the Swainson’s hawk menu. This might include birds as small as a sparrow or as large as sage grouse. One more component to their summertime diet is large insects such as grasshoppers and dragonflies. Swainson’s hawks especially eat a lot of grasshoppers.
Winter
On their winter range, Swainson’s hawks live almost entirely on large insects. A big portion of the large insects they eat are members of the Acrididae family. Acridids include most grasshoppers and locusts. These birds also eat a lot of dragonflies in their winter range. Additionally, some research indicates that they capture dragon flys in flight to fuel their way along their migration route.
Swainson’s Hawk Behavior
Hunting
Swainson’s hawks are soaring raptors. As such, they often hunt as they soar on thermal updrafts, using their powerful vision to search for prey on the ground. They also often still hunt from a high perch as they search for movement from their prey animals. On rarer occasions, they’ll swoop low over the ground as they scan for any prey that they’ve taken by surprise. They’re also very skilled at catching large insects such as dragonflies in the air. They do this with their talons.
Finally, when these birds are in insect hunting mode, they forage as they walk and hop along the ground.
Reproductive Behavior
Swainson’s hawks are monogamous and mate for life until one of the mates dies. They arrive back at their nesting grounds in late March or April. To that end, they often use the same nests from year to year, making minor renovations as they are needed. If they construct a new nest, the male will select the site, and although they both participate in the construction, the male will bring in most of the construction materials. They typically build their nests in isolated trees, but in the absence of a tree, they might also use a power pole, an abandoned homestead building, or an elevated ledge as a nesting site.
Their nests consist of sticks, twigs, and various debris. They are around 2 feet in diameter with an 8 inch round inner bowl. The inner bowl is lined with various soft materials such as leaves, grass, bark, and occasionally cow dung.
In courtship, one of or both members of the pair engage in circling above their nesting site. The male will perform sky dances where he dives steeply toward the ground, then ascending back up to his original altitude, where he repeats the process.
Swainson’s Hawk Life History
The female will lay a clutch of 1 to 4 eggs which she incubates for 34 to 35 days. During this time, the male brings her food and occasionally takes a turn at incubating the eggs while the female eats. Swainson’s hawk hatchlings are altricial at birth. In other words, they are featherless, blind, and helpless. However, their first flight feathers begin to emerge by the time they are 9 to 11 days old, and by the time they’re 37 days old, they will begin to leave the nest for surrounding tree branches. By the time they are 46 days old, they will have fledged. However, they will continue to be dependent on their parents for up to an additional 5 weeks.
After the fledglings and their parents go their separate ways, they will join a group of other first-year birds and eventually migrate south with them.
If they live through their first year, these fledglings can live from 16 to 19 years in the wild.
Also See
We also have the following posts on other Buteo hawks.
