Predation on Hutton's shearwater by stoats: effect of a mast seeding year

Recent research has suggested that predation by stoats (Mustela erminea) probably does not threaten the viability of Hutton's shearwater (Puffinus huttoni) populations. However, no mast seeding years occurred during this research. As mast seeding is usually associated with irruptions in stoat abundance , the impact of stoats might be greater than has been suggested. Widespread mast seeding in autumn 1999 provided the opportunity to measure the mortality rate of adult shearwaters in a mast year relative to that in 3 non-mast years by comparing the density of shearwater carcasses on the ground surface within a breeding colony in each of these four years. Carcass density was calculated using line transect`distance sampling' techniques. No increase in carcass density was detected following mast seeding in 1999. Although the precision of density estimates was low, it is concluded that mast seeding probably does not increase adult mortality enough to threaten the viability of the shearwater colony.