An analysis of migration data from weather-surveillance radars has generated compelling new reasons for preserving patches of natural habitat known as “fire escapes” or “convenience stores.”
The sites typically lack the food resources to fully replenish the energy reserves of migrating landbirds but offer potentially life-saving shelter in otherwise hostile regions, such as developed and agricultural landscapes or coastal areas.
Researchers Jeffrey J. Buler of the University of Delaware and Deanna K. Dawson of the Patuxent Wildlife Research Center in Laurel, Maryland, used data from 16 radars in northeastern states to identify sites that served as stopovers during the fall of 2008 and 2009.
They discovered important areas along the coastlines of Long Island Sound, throughout the Delmarva Peninsula, in areas surrounding Baltimore and Washington, along the western edge of the Adirondack Mountains, and within the Appalachian Mountains of southwestern Virginia and West Virginia.
Local areas often coincided with hardwood forests embedded within landscapes dominated by developed and agricultural lands. For example, bird densities were especially high within Rock Creek Park in Washington, D.C., and Fairmount Park in Philadelphia.
The densities may be due to a “wicking effect,” write the researchers, in which isolated forest patches draw in migrants from the surrounding landscape, concentrating them in a restricted area, but Buler and Dawson speculate that an additional factor may be behind the apparent broad-scale attraction of migrants to cities:
“There is ample evidence,” they write, “that migrating birds are attracted to artificial light from human infrastructure at a local scale, but only scant evidence of attraction to the glow of city lights at a broad scale. At the least, this intriguing possibility that migrants are drawn into urban areas by the intense glow of city lights warrants further investigation.”
Read the paper
Jeffrey J. Buler and Deanna K. Dawson (2014) Radar analysis of fall bird migration stopover sites in the northeastern U.S. The Condor: Ornithological Applications, Volume 116, pp. 357–370.
A version of this article appeared in “Birding Briefs” in the December 2014 issue of BirdWatching. Subscribe.