This study examines the population decline of one of the most common species seen at bird feeding stations across much of North America in winter, the Evening Grosbeak. An irruptive migrant, the Evening Grosbeak occasionally moves out of its boreal and montane breeding areas to winter in lower lati­tudes and elevations. In this study, researchers sought to quantify the extent of changes in the abundance and distribution of Evening Grosbeak popu­lations using Project FeederWatch data gathered between November 1988 and April 2006. Data submitted by participants over the eighteen-year period indicate that reports of Evening Grosbeaks at FeederWatch sites have declined by fifty percent. At locations where the species continued to be seen, the average flock size decreased by twenty-seven percent over eighteen years. While counting birds at feeding stations has proven reliable for monitoring population trends, factors contributing to recent decreases in the abundance of Evening Grosbeaks at feeders in winter remain unclear due to a lack of basic life-history information. Understanding the factors influencing Evening Grosbeak populations, such as breeding biology and reproductive success is critical to developing conser­vation plans and reversing current population trends. The authors contend that urgent investigation is warranted in determining the factors that are driving these declines given the geographic extent and rapid rate of observed population changes.

This article was written by David N. Bonter, Leader of Project FeederWatch and Michael G. Harvey of the Department of Ecology and Evolutionary Biology at Cornell University.  It appeared in the May 2008 issue of The Condor, an international journal that publishes scientific articles on the biology of wild species of birds.