Swainson's Hawk - Ecology

Ecology

The habitat of Swainson's Hawk consists of open and semi-open country – deserts, grasslands and prairies – in both its breeding and wintering ranges. It favors wild prairie, hayfields, and pastures over wheat fields and alfalfa fields, which may offer its prey too much cover. It requires elevated perches for hunting and a supply of small mammals such as young ground squirrels as prey for its nestlings. The breeding distribution of Swainson's Hawk is tied very closely to the distribution of various small mammals for this reason. In Saskatchewan, for example, the distribution of Richardson's Ground Squirrel and Swainson's Hawk are precisely the same.

Swainson's Hawk will defend its breeding territory from other buteos. Breeding densities may vary from one area to the next but averages one pair per 2.5 square miles (6.5 km²). The average home range estimate for this hawk is 1 to 2 square miles (2.5 to 5 km²). It gathers in groups for feeding and migrating. However, in each case, such gathering is not social, but motivated by good feeding or migrating conditions.

Swainson's Hawk, the Red-tailed Hawk (B. jamaicensis) and the Ferruginous Hawk (B. regalis) compete for territory, and defend territories against each other. In many parts of the plains these three species nest in the same general area and exploit much the same prey base. Although diets overlap greatly, habitats may not overlap as much. In Oregon, Swainson's Hawk selects nesting trees having a different configuration than those used by Red-tailed or Ferruginous Hawks. In southern Alberta, different nesting habitats help reduce food competition, with Swainson's Hawk favoring areas with scattered trees or riparian borders, while Red-tailed Hawks nest in stands of tall trees, and Ferruginous Hawks nest on the open plains.

Reduced reproductive success may result from Swainson's Hawk's nesting proximity to these two other buteos. Swainson's Hawk is generally tolerant of people. The bird is attracted to haying, mowing, and plowing operations. House Sparrows, European Starlings, and other small birds may nest in or near a Swainson's Hawk's nest.

In winter quarters, they are far more tolerant, though many birds will still fend for themselves. In Uruguay, the species likes largely open but broken (with rocks or woods) plains or low hills, where it can be seen to gather in larger groups. Groups of a few dozen birds are not uncommon. Flocks of over one hundred birds have been recorded several times, e.g. one that roamed the Cuchilla Marincho region south of Andresito (Flores Department) in mid-late December 2005.