Maine Coastal Islands National Wildlife Refuge worked in collaboration with the University of Maine's Lab of Avian Biology to examine how physiological condition is affecting Arctic and common tern population recovery rates at Petit Manan Island, Maine. Graduate student Stephen Agius examined the mobilization of fat (anabolic vs. catabolic) and circulating levels of a baseline stress hormone (corticosterone) throughout the prebreeding and breeding periods, 2005-2007.

It was found that the longer distant migrant, Arctic terns (annual migration ~40,000 Km), arrived at the breeding ground in a poorer condition than common terns. Birds that arrived in poorer condition were less able to improve their condition throughout the breeding season. Birds that remained in poor condition were more likely to abandon breeding attempts. Overall, terns that arrived in an improved condition were better able to maintain their condition throughout the breeding season, and therefore had a much higher rate of seasonal reproductive success. The inability of Arctic terns to maintain energy reserves at a critical threshold from the prebreeding to the breeding period may have had a greater affect on their breeding success.

This study illustrates that resource managers working to restore tern populations in the Gulf of Maine need to take into account the impact of events (food availability and weather conditions) during the wintering and migration periods as well as on the breeding grounds to understand differences in population recovery rates.