Attendance and Diet in Relation to Breeding Success in Herring Gulls (Larus argentatus)

Abstract

Breeding success was studied in relation to time partitioning, and diet, in Herring Gulls (Larus argentatus) on Terschelling, The Netherlands, in 1992. The average fledging success of 0.5 chicks fledged/pair (n = 26 pairs) was lower than in the 1960s. We suspect that increased conspecific predation of eggs and chicks was the result of local food shortages. Successful pairs differed markedly in attendance patterns and diet from unsuc- cessful pairs. Unsuccessful pairs traveled to the feeding grounds more frequently (pre-egg and egg stages), and left the territory unguarded, for longer periods of time (egg and chick stages) than successful ones. Feeding frequency of chicks was significantly higher in successful pairs and was accompanied by higher growth rates in chicks. Overall, successful pairs ate more fish and chicks of conspecifics and Lesser Black-backed Gulls (L. fuscus) than unsuccessful ones, while the latter generally ate more crabs and starfish. Chicks of pairs that did not change their diet at hatching suffered higher mortality than chicks of pairs that did. We suggest that the deteriorating feeding conditions on Terschelling since the late 1960s has resulted in less synchronous territory attendance within pairs and less adequate feeding behavior, resulting in high levels of conspecific predation and relatively poor chick growth. Received 20 June 1995, accepted 20 August 1995.