Young southern Red-tails make surprising northbound migrations each summer

Contrary to the widely held belief that southern populations of Red-tailed Hawks don’t migrate, a 42-year study of Red-tails in southwestern California has revealed not only that they migrate, but that they fly north, not south.

Before the birds turn four years old, they embark on annual summer sojourns, traveling as much as 900 miles (1,460 km) from where they hatched. Then, in late summer or fall of the same year, they head back south to spend the winter in their natal area. Once the hawks find mates and establish territories, their migrations come to an end.

The finding is based on encounters with 64 Red-tails that were banded as nestlings and 16 fledglings that were fitted with backpack-mounted satellite transmitters. Most of the hawks hatched within a five-county area between Los Angeles and San Diego from 1970 through 2009. The birds flew as far north as Oregon, Idaho, Montana, Utah, and Yellowstone National Park.

The research was led by internationally recognized raptor expert Peter H. Bloom. He and his colleagues compared their data with that for all other Red-tails banded as nestlings in North America since 1940. They discovered that hawks that were reared north of a line extending east from around San Francisco (38°N latitude) were most likely to migrate south. Birds reared south of the line tended to migrate north in summer, just as the birds from southwestern California had.

The movements are surprising but not unheard of. Bald Eagles from Florida, Texas, Arizona, and northern California make northbound journeys in summer, too, as do female Prairie Falcons that nest in southwestern Idaho. Bloom and his colleagues write in the March issue of the Journal of Raptor Research that a reduced availability of prey in southern regions in the warmer months is a primary reason for the flights of all three species.

See photos of Red-tailed Hawk.

A version of this article appeared in the June 2015 issue of BirdWatching magazine. Subscribe.

Originally Published May 4, 2015