Which bird of prey forms huge autumn flocks at Veracruz during migration?

The broad-winged hawk forms huge autumn flocks at Veracruz during migration.

Broad-winged hawks breed in forested areas of eastern North America and migrate south to Central America and northern South America. In autumn, many follow mountain ridges and coastlines where rising air helps them travel efficiently.

The Veracruz River of Raptors project documents one of the world’s most spectacular concentrations of migrating birds. Hundreds of thousands of raptors, including broad-winged hawks, can pass through the region during the season.

Unlike many falcons, broad-winged hawks rely heavily on soaring rather than continuous powered flight during migration. They use thermals and other updrafts to reduce energy costs, which helps explain their tendency to gather in visible streams and kettles.