Autumn migration of North American landbirds

Posted by Libby Ellwood

As you've recently been reading on this blog, autumn is the neglected season of phenology research. Recognizing this issue, a few members of the Primack lab family (Richard, Amanda and Libby) and our good friend and colleague at the Manomet Center for Conservation Science, Trevor Lloyd-Evans, wondered if and how the timing of autumn bird migration was changing in Massachusetts. We were curious how the longer growing season, delayed leaf senescence in trees, and increased availability of insect food sources that can accompany warmer weather would impact birds' migration to southern wintering grounds.

Gray catbird in the hands of a volunteer bander at Manomet Center for Conservation Science

To explore this, we used data of 37 bird species from the Manomet bird banding program between August and November from 1969-2012. We found that 14 species have migration dates correlated with temperature: 13 are migrating later with warmer temperature and one, the gray catbird, migrates earlier with warmer temperature, as you can see in the figure below.

The relationship between mean stopover dates and changes in stopover date with August + September temperature for species demonstrating significant changes in stopover with temperature. The x-axis represents the mean stopover date of the species over all years, and the y-axis represents the slope of stopover date and temperature, days °C–1. Species abbreviations are standardized codes: BHVI (Blue-headed Vireo), REVI (Red-eyed Vireo), BRCR (Brown Creeper), RCKI (Ruby-crowned Kinglet), SWTH (Swainson’s Thrush), HETH (Hermit Thrush), AMRO (American Robin), GRCA (Gray Catbird), COYE (Common Yellowthroat), AMRE (American Redstart), BLPW (Blackpoll Warbler), MYWA (Myrtle Warbler), WTSP (White-throated Sparrow), and SCJU (Slate-colored Junco).



All in all, autumn bird migrations are quite variable and species are responding in different ways to a changing climate.  Further, it appears that some bird species may respond differently to autumn environmental cues than plants and insects, which has implications for the success of individual species and the ecosystem as a whole. Read more about this study here.