Do Co-Nesting Arctic and Common Terns Partition Foraging Habitat and Chick Diets?

Abstract

We identified foraging locations during a two-year radio telemetry study (2003-2004) and described chick diets over a seven year period (1999-2005) for co-nesting Arctic (Sterna paradisaea) and Common Terns (Sterna hirundo) at Country Island, Nova Scotia, Canada. The results of the radio telemetry study showed that both species foraged within nine km of the breeding colony, however, Arctic Terns foraged in deeper water on the seaward side of the colony while Common Terns foraged in relatively shallow water between the colony and the mainland. The results of the diet study showed that chick diets overlapped significantly, with both species feeding mostly on hake (Urophycis sp.) and sand lance (Ammodytes sp.). Despite the overlap in diet, Arctic Terns delivered proportionally more hake and less sand lance than Common Terns and the sand lance they delivered were smaller on average than those delivered by Common Terns. Overall, Arctic and Common terns at this site show foraging habitat segregation, but similar chick diets.