Using stable-isotope analysis of feathers to distinguish moulting and breeding origins of seabirds

To determine whether stable isotope measurements of bird feathers can be us ed to identify moulting (interbreeding) foraging areas of adult seabirds, w e examined the stable-carbon (delta(13)C) and nitrogen (delta(15)N) isotopi c composition of feathers of chicks and adults of black-browed albatrosses (Diomedea melanophrys) from Kerguelen Islands, southern Indian Ocean. Albat ross chicks are fed primarily fish (75% by mass), the diet being dominated by various species of the family Nototheniidae and Channichthyidae which co mmonly occur in the shelf waters in the vicinity of the colony. delta(13)C and delta(15)N values in chick feathers, which are grown in summer in the b reeding area, were lower than values in adult feathers, which are grown in winter (delta(13)C: -19.6% versus -17.6% and delta(15)N: 12.4% versus 15.7% , respectively). No differences in delta(13)C and delta(15)N values were fo und in adult wing feathers moulted in 1993 and 1994 and in adult feathers f ormed at the beginning, middle and end of the 1994 moulting period. These d ata are consistent with adults moulting in the same area and feeding at the same trophic level from one year to the next and with no major changes in foraging ecology within a given moulting season; they suggest that foraging grounds were different in summer and winter and that these differed in the ir stable-isotope signature. Changes in both feather delta(13)C and delta(1 5)N values indicated feeding south of the Subtropical Front (STF) during ch ick rearing, which is in agreement with the known foraging ecology at this time and feeding north of the STF during moult. This, together with band re coveries from adult birds, indicates that black-browed albatrosses from Ker guelen Islands wintered in subtropical waters off southern Australia. The s table-isotope markers in feathers, therefore, have the potential for locati ng moulting areas of migratory seabird: species moving between isotopically distinct regions and for investigating seabirds' foraging ecology during t he poorly known interbreeding period. Such information is needed for studie s of year-round ecology of seabirds as well as for their conservation and t he longterm monitoring of the pelagic environment.