Swainson’s Hawk

Physical Characteristics

The Swainson’s Hawk (Buteo swainsoni) is a long-winged, slender buteo of the open plains and prairies of western North America, renowned for its long-distance migrations.

• Plumage:
  Highly variable, with light and dark morphs.

  • Light morphs: pale underparts with a contrasting dark chest band and dark flight feathers.

  • Dark morphs: nearly all chocolate-brown with paler flight feathers.
    Both morphs show a distinctive two-toned underwing pattern in flight.

• Face: Pale with a darker cap and malar stripe in light morphs. Bill is hooked with a yellow cere; eyes are dark brown.

• Body: Slimmer and lighter than most buteos, built for endurance soaring rather than stocky power.

• Wings: Long and pointed for a buteo, giving it a falcon-like silhouette. Its broad soaring style makes it highly efficient during migration.

• Tail: Long, generally grayish with multiple dark bands and a broader subterminal band.

• Feet: Yellow with sharp black talons, suited for grasping small mammals and insects.

Size:

• Length: About 18 to 22 in (46 to 56 cm).

• Wingspan: Between 46 to 54 in (117 to 137 cm).

• Weight: Ranges from 1.5 to 3 lbs (700 to 1,400 g), with females larger than males.

The Swainson’s Hawk’s long wings, slim frame, and distinctive two-toned underwings make it one of the most recognizable raptors of the western grasslands.

Reproduction

The Swainson’s Hawk breeds across the wide-open prairies and grasslands of western North America, favoring habitats with scattered trees or utility poles for nesting.

1. Mating and Courtship:

   • Swainson’s Hawks are generally monogamous, forming long-term pair bonds.

   • Courtship involves soaring displays, diving flights, and mutual calling. Pairs often return to the same nesting territory each year.

2. Nesting:

   • Nests are built in trees, shelterbelts, shrubs, or on man-made structures such as windbreaks or poles.

   • Nests are constructed of sticks and lined with grasses, leaves, and softer vegetation.

   • Pairs frequently reuse and enlarge nests annually.

3. Egg Laying and Incubation:

   • The female lays 2 to 4 eggs, pale bluish-white with brown blotches.

   • Incubation lasts 34 to 35 days, performed mostly by the female, while the male provides prey.

4. Chick Development:

   • Chicks hatch covered in down and are brooded by the female for the first week.

   • The male supplies food, which the female tears into small pieces to feed the young.

5. Fledging and Independence:

   • Young fledge at about 38 to 46 days but continue to rely on parents for food and hunting lessons for several weeks after leaving the nest.

The Swainson’s Hawk’s reproductive success depends on healthy populations of small mammals and insects, which provide the primary food supply for raising young.

Lifespan

The Swainson’s Hawk (Buteo swainsoni) is a long-distance migrant with a moderate lifespan that reflects both natural challenges and hazards faced along its migration routes.

• Lifespan in the Wild:
  Swainson’s Hawks typically live 8 to 12 years, with some reaching up to 15 to 18 years. Many juveniles, however, do not survive their first year due to starvation, predation, or hazards encountered during their first migration.

• Lifespan in Captivity:
  In captivity, with access to steady food and veterinary care, they may live up to 20 years or more.

Threats to the Swainson’s Hawk:

• Migration Hazards: Their extraordinary migration of up to 12,000 miles (19,000 km) exposes them to exhaustion, storms, and loss of stopover habitats.

• Pesticides: In South America, pesticide use on crops has historically caused mass mortality in wintering grounds.

• Predation: Eggs and nestlings are vulnerable to raccoons, snakes, and Great Horned Owls. Adults face predation mainly from larger raptors.

• Human Hazards: Collisions with vehicles, electrocution on power lines, and habitat conversion from prairie to farmland also pose risks.

Despite these pressures, conservation efforts and adaptability to agricultural landscapes have helped keep Swainson’s Hawk populations relatively stable in many regions.

Eating Habits

The Swainson’s Hawk is an adaptable hunter whose diet shifts seasonally, reflecting its wide-ranging migration from North to South America.

• Diet:

  • In the breeding season, they primarily eat small mammals such as ground squirrels, gophers, and voles.

  • During migration and in wintering grounds, their diet shifts dramatically to large insects, including grasshoppers, crickets, and dragonflies.

• Foraging Strategy:
  Swainson’s Hawks hunt both from perches and while soaring over open fields. They are also known to forage cooperatively in flocks, particularly when pursuing swarms of grasshoppers.

• Hunting Behavior:
  They dive from flight or perch to seize mammals with their talons, but in South America, they often swoop and snatch insects directly from the ground or in flight.
  Their long wings allow them to hover briefly, glide low, or circle fields when hunting.

• Feeding the Young:
  During nesting, males deliver small mammals to the nest, and the female tears food into smaller portions for chicks.

• Seasonal Variation:

  • Summer (North America): Mammals dominate the diet to provide high protein for raising young.

  • Migration/Winter (South America): Insects become the primary food source, with hawks often forming large flocks that feed on grasshopper swarms.

The Swainson’s Hawk’s dramatic dietary shift—from mammal hunter in summer to insect specialist in winter—is one of the most unique feeding adaptations among raptors.

Uniqueness

The Swainson’s Hawk (Buteo swainsoni) stands out among raptors for its extreme migrations and unusual feeding strategies:

• Extraordinary Migration: Travels up to 12,000 miles (19,000 km) between breeding grounds in North America and wintering areas in South America, one of the longest migrations of any raptor.

• Dietary Shift: Uniquely shifts from a diet of mammals in summer to mostly insects in winter, feeding in flocks on grasshopper swarms.

• Flocking Behavior: Unlike most hawks, it often forms large flocks during migration and while feeding, sometimes numbering in the thousands.

• Long, Slim Wings: Its long, pointed wings give it a falcon-like silhouette and exceptional efficiency for soaring over vast distances.

• Prairie Specialist: Closely tied to open-country habitats, especially western prairies, grasslands, and agricultural fields.

• Adaptability to Agriculture: Frequently hunts over croplands, benefiting from insect outbreaks in farm fields.

The Swainson’s Hawk’s insect-based winter diet, mass flocking behavior, and epic migration make it one of the most remarkable and unique hawks in the world.