CELS Grad Student Links Behavior to Diet in Songbirds on Block Island

URI doctoral student Clara Cooper-Mullin removes a bird from a net on Block Island as part of her research. (Photo by Todd McLeish)

KINGSTON, R.I. – November 9, 2016 – University of Rhode Island doctoral student Clara Cooper-Mullin spent this year’s entire fall bird migration season in a tiny cramped structure on Block Island that doubled as her living quarters and bird banding station. But her work there is revealing new insights into why birds behave the way they do during migration.

“I’m looking at whether their body condition is a factor in the way the birds behave at migration stop-over points like Block Island,” explained Cooper-Mullin, who grew up in Irvington, N.Y. “Birds are mostly consuming fruit during migration, so I’m trying to figure out what they’re getting out of the fruit and how it influences their behavior as they leave.”

Her study follows up on one conducted at the same site by a previous URI graduate student, Adam Smith, who found that hermit thrushes in good physical condition moved around less when they stop at Block Island, presumably because they didn’t have to feed much, and they were more likely to go straight south when they departed the island. Hungry birds typically spent more time on the island feeding and continued their migration by following the coastline.

Working in collaboration with URI Professor Scott McWilliams, Cooper-Mullin focused her field work this year on blackpoll warblers, which migrate from the boreal forests of Canada to the Caribbean by undertaking a three-day flight over the ocean from southern New England.

Every day, she and research technician Olivia DaRugna captured migrating blackpolls and placed them in temporary cages where they were fed a special diet for several days before being released. Some were fed as much food as they could eat, while others were fed just enough to keep them in the same thin condition they arrived in. The researchers then monitored the behavior of the released individuals as the birds prepared to continue their migration.

“Blackpolls fatten up really fast,” said Cooper-Mullin. “The reason they’re trying so hard to fatten up is because they’re about to leave here and go straight over the water for several days. They need that body condition to get ready to fly.”

By contrast, red-eyed vireos – another species she is studying for comparison – take their time eating. They typically spend most of their migration flying over land…[Read more]