Common Guillemot Uria aalge chick diet and breeding performance at Sumburgh Head, Shetland in 2007–09, compared to 1990–91

Abstract

Chick diet of Common Guillemots Uria aalge was studied by direct observation at Sumburgh Head, Shetland during 2007–09. Lesser Sandeels Ammodytes marinus comprised 55% of prey items, the remainder being Gadidae, including Whiting Merlangius merlangus and Saithe Pollachius virens, and a few Snake Pipefish Entelurus aequoreus. This contrasts with 1990–91 when chick were fed 80% sandeels, the remainder mostly being unidentified Gadidae. When this shift from a diet dominated by sandeels took place is unknown, but a similar shift in chick diet at Fair Isle (40 km southwest of Sumburgh Head) seems to have occurred some time during 2000–02. Since 2003, weights of chicks near fledging have been lower than during the 1990s, and average breeding success has been reduced.