ABSTRACT: Stable isotope ratios of nitrogen (¹⁵N/¹⁴N) and carbon (¹³C/¹²C) 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 locations delta¹⁵N values declined over time indicating a shift in fulmars to a lower trophic status. Similarly, delta¹³C signatures declined over time. These findings are consistent with a change in diet from prey of relatively high trophic status, possibly 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.

KEY WORDS: Stable isotopes . Northern fulmar . Temporal trends . Diet . Mesopelagic prey

Published in MEPS Vol. 125 (1995) on September 14
ISSN: 0171-8630. Copyright © Inter-Research, Oldendorf/Luhe, 1995