An email special alert caught my attention this week. Hawk Mountain Bird Sanctuary (located in Pennsylvania about 85 miles due west of New York City) announced that 2361 broad winged hawks had been counted as they streamed past the rocky outcrop known as the South Lookout. All in ONE HOUR! (between 10:00 and 11:00 am on the 18th of September).
Migration is a long distance movement between a breeding area and a non breeding range. Local, seasonal, and nomadic bird travel is not migratory. Nor are irruptions, which usually occur due to cyclical food supply shortages, or dispersal movements of young birds.
Broad-winged hawks are one of only a few of the North American hawks which are classed as complete migrants, defined as a bird which completely vacates its breeding territory for a winter range. Osprey, swallow-tailed and Mississippi kites, and rough-legged and Swainson's hawks are our only other complete migrant hawks. Although many complete migrant species fly long distances like the broad-winged hawk which winters in Peru, the rough-legged hawk moves only from the Arctic to the US-Canada border area.
Most of the hawks common to these parts are classed as partial migrants (for example red-tailed, Cooper's and sharp-shinned, goshawks, red-shouldered, merlins, kestrels, northern harrier, and eagles), which retreat from part of their range but may remain resident in one part. Open water, garbage dumps, land fills and sewage treatment lagoons all tend to facilitate partial migration and may be one reason for the increased presence of eagles and turkey vultures in more northerly regions than previously encountered.
Only a few hawk species from the southern states are non migratory, year round residents of a home range. California condors, white-tailed kites, and crested caracaras are considered to be in this category.
Obviously the nature of migration is much more complicated than the simplistic common thought of north in summer, south in winter for partial migrant bird families. A study of the colored range maps for hawks in your bird guide will indicate the overlapping of winter, summer, and year round ranges. In some cases a bird species is present year-round, but the residents in the summer are not the same as the winter dwellers.