Seasonal variation in the diet of stoats in a breeding colony of Hutton's shearwaters

The diet of stoats (Mustela erminea) was studied in the Kowhai valley colon y of Hutton's shearwaters (Puffinus huttoni). Remains of Hutton's shearwate rs were found in 785 of 788 seats examined. Scars contained remains of eggs , chicks, near fledging age chicks and adult shearwaters, as well as the re mains of skinks (Oligosoma sp.) and weta (Deinacrida sp.). There was season al variation in the frequency of occurrence of all major prey items. Stoats switched from taking predominantly adults during the pre-egg and incubatio n periods, to taking almost exclusively chicks during the chick-rearing per iod. The impact of stoats on Hutton's shearwaters may as a consequence of t his prey switch be reduced, because the population is likely to be more aff ected by the loss of adults rather than chicks. Stoats continued to feed up on shearwaters, even after all birds had left the colony. Remains of mice ( Mus musculus) and hares (Lepus europaeus) were infrequently found in seats, although the occurrence of these along with the occurrence of skinks and w eta increased after all live shearwaters had departed. The results suggest that stoat numbers may be limited by the availability of over-winter prey w ithin the colony.