Seasonal Cycles: Migratory Birds

Many people are enthusiastic about the return of familiar birds in the spring from their southern wintering grounds. Concord has the longest records of bird arrival dates in North America. This record begins with observations made by Thoreau, and has been continued until the present by a number of Concord residents over the past century and a half. These records have been analyzed to determine whether climate change is affecting bird migration timing the way it is with plant flowering times and insect emergence.

As a group, bird species tend to be less responsive to the effects of climate change than local plants and insects. Some bird species are responding to climate change by arriving in Concord earlier in warmer years than colder ones, but others have not changed their arrival dates, and a few species are even arriving later. Other species that used to migrate now spend all year in Concord, a change made possible in part by people putting out bird feeders. Because migratory birds as a group are responding to climate change at a different rate than plants and insects, there is the possibility that birds returning to Massachusetts may miss the peak abundance of their insect food source.