The migration of raptors has begun, and one of the first species to migrate in the fall is the Broad-winged Hawk (Buteo platypterus). While it is quite secretive when nesting, it is one of the more conspicuous species of birds when migrating. This is for two reasons. They are one of the few North American raptors that flocks during migration, and much of their migratory behavior is concentrated in the Northeast in a two-week period around the middle of September.
Migrating Broad-wings conserve energy by frequently soaring in thermals and mountain updrafts. Flocks of birds, or “kettles”, soar up the heated columns of air, peel off and glide to the next thermal where they repeat the process. Very little wing-flapping is necessary in order to cover a lot of ground. The flocks, or “kettles,” range from several individuals to thousands of birds (larger kettles generally occur nearer their Central and South America wintering grounds).
The number of birds migrating often grows following a cold front, when winds die down and thermals increase. Fall migration of Broad-wings in the Northeast is associated with good visibility, moderate favorable winds, high temperatures, and afternoons (vs. mornings). (Photo: juvenile Broad-winged Hawk)
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Broad-winged Hawk chicks spend their first five or six weeks in the nest being fed small mammals, toads, nestling birds and a variety of invertebrates by their mother. They then fledge, but for the next two weeks these young birds continue to use the nest as a feeding (food is still being provided for them) and roosting site. At about seven weeks of age they begin capturing their own prey, and remain on their parents’ territory for the next month or two — just enough time to learn the ropes before migrating south for the winter, which they are doing right now (peak migration is mid-September).