April 13, 2011

Spring migration

All migratory song birds travel various distances each year. Migration is determined by the extent of both the summer breeding range (how far north) and wintering range (how far south). These distances in turn are based on food availability, appropriate breeding habitat, and competition. These migratory ranges are partially illustrated by the rainbow sherbet “range maps  found in most every U.S. field guide. Most of these small range maps depict the U.S. and Canada and show distribution during a particular season usually defined as “winter”, “breeding”, and “year round” as represented by bands of color. These maps are useful to bird watchers as they show if a bird is likely to be around the neighborhood in a given season. What these maps fail to do is illustrate the extent and timing of migration, the smaller seasonal shifts within the “year round” area, and irruptions in which a particular bird is driven out of their normal range by a lack of important food source such as pine cones. There are several online tools that bird watchers will find useful in illuminating the full story of songbird migration as illustrated in range maps.

Ebird – has recently animated their extensive bird sightings database to show an incredible algae bloom of bird migration.

Watch the Northern cardinal’s near steady presence in the Eastern, Lower 48. While the Bobolink, who journeys from as far away as Argentina makes it’s summer home in New England. Compare these two species with the Blackpoll warbler who only passes through New England en route to the barren taiga of Northern Canada to breed. As the Blackpoll warbler comes from further away it arrives in the second half of May. Compare this to the Palm Warbler, who migrates from the Caribbean and Florida and arrives in New England weeks before the Blackpoll as early as mid-April.  

New England is also home to winter residents. Watch the inverted migration of the White throated sparrow that leaves the cozy confines of New England and the southern Appalachians in April for a summer breeding in Canada, only to return come September for the winter.

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is an educator, bird watcher, and writer fascinated by the intersections of place, people, nature, and culture. He works for Mass Audubon and lives in the heart of Massachusetts. For questions or comments please contact: alexanderjosephdunn@gmail.com

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