Winter locations of red-throated divers from geolocation and feather isotope signatures

Proof of concept evidence that stable isotopes of carbon, nitrogen and sulphur may identify individual kittiwakes breeding in different colonies

RATIONALE

Carbon, nitrogen and sulphur stable isotopes in feathers grown by seabirds while breeding reflect the local isoscape and diet in the vicinity of the colony, so may make it possible to discriminate individual birds from different colonies.

METHODS

Black-legged kittiwake Rissa tridactyla inner primary feathers from two colonies about 350 km apart in the North Sea were used to test whether δ13C, δ15N and δ34S differed between individuals from the two colonies. Feather tips cut from breeding birds caught at nests were compared with tips of moulted feathers (grown 1 year earlier) found on the ground.

RESULTS

Isotopic compositions showed no overlap between the two colonies in δ13C, δ15N or δ34S in tips of newly-grown feathers sampled from breeding adult kittiwakes. There was some overlap in δ13C, δ15N and δ34S from moulted feathers, but discriminant analysis allowed >90% of individuals to be assigned to their colony. In five of six comparisons, mean isotopic compositions were the same in new and moulted feathers but not for δ34S at one of the two colonies.

CONCLUSIONS

This study has demonstrated for the first time that stable isotopes in inner primary feathers of kittiwakes can allow accurate identification of the breeding colony of individual birds from two different colonies within the North Sea. Further research is required to determine if this method can be applied with greater spatial resolution and to a larger number of colonies.