Climate change is predicted to increase the frequency and severity of extreme climate events, and it is important that we understand how this might affect natural systems. We examined the effects of extreme climate events on adult survival rates in three species of auks breeding on Triangle Island, British Columbia: Cassin's Auklet (Ptychoramphus aleuticus), Rhinoceros Auklet (Cerorhinca monocerata), and Tufted Puffin (Fratercula cirrhata). Our 15-year study period (1994–2008) included two extreme climate events: a strong El Niño event in 1997–1998 and an atmospheric blocking event in 2005. Neither event had any detectable effect on the annual adult survival rate (± 95% confidence interval) of either Tufted Puffins (females: 0.96 ± 0.05; males: 0.91 ± 0.06) or Rhinoceros Auklets (0.86 ± 0.02 in both sexes). By contrast, the adult survival of female Cassin's Auklets was halved during both extreme climate events (from a background rate of 0.84 ± 0.05 to 0.44 ± 0.10), whereas survival of males was low, but constant through time (0.75 ± 0.03). Our results, combined with those of previous studies, suggest that the major ongoing decline in the Cassin's Auklet population on Triangle Island is driven by negative effects of climatic variation on both reproductive success and the survival of adult females. Climate change may result in continued Cassin's Auklet population declines at this and more southerly colonies. By contrast, the relative stability of Rhinoceros Auklet and Tufted Puffin populations is likely attributable to the resiliency of adult survival rates to climatic conditions.
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Vol. 128 • No. 4