Getting the Migration Timing Right - Page 1

An experienced bird-watcher can mark the seasons in a given locale by the highly predictable times of arrival and departure of familiar migrating birds. Across much of the United States, for example, the first sign of spring is the arrival of flocks of Re-winged Blackbirds. The seasonal timing of migration is closely related to the likelihood that the necessities of life will be available at the time of arrival. Within each family of birds, however, there are great differences in timing among species. For example, among American wood warblers, the Louisiana Waterthrush may arrive at its breeding ground a full two months before the Connecticut Warbler passes through.

Variation also exists in the pace of migratory travel, even among related species. Shorebirds, waterfowl, cranes, and other species that use traditional stopover areas tend to make long flights interrupted by days of layover. Many land birds that are able to enjoy an abundance of resting and feeding habitats, such as warblers, flycatchers, and sparrows, typically fly one night, then rest for two or three nights, depending on the weather. These more leisurely travelers might cover as n\many as 2000 miles in a night;s flight, especially if they have a tail wind. Some of these same kinds of birds are capable of making extended flights if, for example, they have to cross a large body of water.