UC Irvine

Applications of the model to populations of Brunnich's guillemot Uria lomvia, common guillemot U. aalge, red-legged kittiwake Rissa brevirostris, and black-legged kittiwake R. tridactyla breeding on the Pribilof Islands suggest that guillemot mortality is greatest following perturbations located in shallow inshore areas about the breeding islands, while kittiwakes are less severely affected by localized perturbations but are sensitive to spills occurring over a wider area about the islands. Model explorations employing chronic low-level pollution rather than one-time perturbations suggest that the guillemot population breeding on St. George Island could tolerate an overall reduction of 10% in the food supply without suffering a major decline in fledging success, but a reduction of 40% would lead to total reproductive failure in the colony. The effects of one-time mortality on guillemots are much more severe if adults rather than first-year birds suffer the mortality. If a given level of one-time mortality is superimposed on a chronic low-level change in survivorship or fecundity, recovery times are markedly longer.-from Authors