Diets and long-term changes in delta15N and delta13C values in northern fulmars Fulmarus glacialis from two northeast Atlantic colonies

Abstract

Stable isotope ratios of nitrogen (15N/14N) and carbon (I3C/l2C) were determined in feather samples from northern fulmars Fulmarus glacialis sampled at around the turn of the century and in 1993 from 2 northeast Atlantic colonies. At both locabons 6I5N values decllned over time indicating a shlft in fulnlars to a lower trophc status. Similarly, 613C signatures declined over tlme. These findings are consistent with a change in diet from prey of relatively high trophic status, posslbly involving the utilisation of offal from whaling activities around the turn of this century, to contemporary prey of lower trophic status. Contemporary dietary information from fulmars at both sites accords with feather isotopic signatures. Two prey species recorded in the diet of fulmars from St Kilda can be considered mesopelagic and have not been noted in seabird diets previously. This is the first study to show that stable isotopes in feathers can be used to determine long-term changes in bird diet.