Non-random nestling mortality in northern fulmars: implications for monitoring marine environments

Abstract

Chick growth and food provisioning of northern fulmars Fulmarus glacialis were studied at Fair Isle, Shetland, in 2 years of contrasting environmental conditions. Low sandeel Ammodytes marinus availability resulted in very low breeding success in many seabirds in Shetland in 1998, whereas breeding success in 1997 indicated a normal season. Fulmars at Fair Isle experienced lower chick survival in 1998 than in 1997. There were also significant differences in diet and food provisioning in the 2 years; sandeels were the most abundant prey items in 1997, but were completely absent from the diet in 1998. High nestling mortality occurred shortly after hatching in 1998. Those chicks that survived this episode had previously been heavier for their age, and remained heavy throughout development in comparison to chicks in 1997, despite a continued absence of sandeels from the diet. Surviving chicks in 1998 were subsequently fed comparatively small meals at frequent intervals, but with no overall difference in the amount of food delivered. We discuss the implications of differential mortality and resulting growth patterns for the use of seabird breeding parameters to monitor marine environments.