Seabird Breeding Performance during Two Years of Delayed Capelin Arrival in the Northwest Atlantic: A Multi-Species Comparison

Abstract

-Breeding performance and timing of breeding of six seabird species breeding in the northwest Atlantic were compared during 1992 and 1993 when oceanographic anomalies and changes in fishing practices provided an opportunity to compare effects of reduced food availability at a multi-species level. The inshore spawning migration of capelin (Mallotus villosus), a major prey for five of the six species considered here, was delayed by one month in 1992 and 1993, and a ground fisheries moratorium eliminated the production of fish offal, an important alternative food source for Larus gulls and Black-legged Kittiwake (Rissa tridactyla). Inshore, surface-feeding piscivores, kittiwake and Herring (L. argentatus) and Great Black-backed (L. marinus) gulls, had lower breeding success than did pursuit-diving Atlantic Puffin (Fratercula arctica) and Common Murre (Uria aalge). Breeding performance of Leach's Storm-Petrel (Oceanodroma leucorhoa), an offshore, surface-feeding planktivore, appeared unaffected by nearshore perturbations. Hatching, fledging and breeding success of inshore surface-feeders were much reduced while those of pursuit divers were similar to previous years when ocean conditions were normal. Later breeding in 1993 than in 1992 for kittiwakes and Herring Gulls resulted in more chicks of these species hatching after mature capelin became available, with subsequent higher breeding success. Results support the hypothesis that inshore surface feeders are more sensitive to changes in food availability than are pursuit-divers and offshore surface-feeders, and demonstrate the importance of timing of breeding in relation to temporal changes in prey availability. Received 23June 1998, accepted 31 October 1998.