Composition, Spatial and Temporal Variation of Common and Arctic Tern Chick Diets in the Gulf of Maine

Abstract

-From 1990-1997, we observed food deliveries to Common (Sterna hirundo) and Arctic (S. paradisaea) tern chicks in the Gulf of Maine; deliveries were observed at four Common Tern colonies from 1991-1997 and at three Arctic Tern colonies from 1990-1997. Dietary overlap was high, 0.812. Fish comprised over 96% of the prey delivered (frequency) to Common Tern chicks. In contrast, Arctic Tern chicks were fed a diet consisting of 65% fish and 35% invertebrates. Although the two terns fed different proportions of fish, both species relied heavily on white hake (Urophycis tenuis), Four-bearded rockling (Enchelyopus cimbrius) and Atlantic herring (Clupea harengus). American sand lance (Ammodytes americanus) was an important prey for Common Terns at one island. Overall, Common Terns fed their young a greater diversity of prey than did Arctic Terns. We found significant inter-annual and intercolony differences in the diversity and proportions of prey types. Boom and bust years were evident for particular prey. We suspect dietary differences in Maine were due to colony location; however, a detailed study of the relationship between prey availability and abundance and the foraging ecology of terns in Maine is needed to elucidate these relationships. We believe long-term diet data sets gathered from multiple sites are the best way to characterize waterbird diets. Received 11 October 1999, resubmitted 6 April 2000, accepted 8 April 2000.