Eleven after-second-year Cassin's Auklets (Ptychoramphus aleuticus), 10 of them females (91%), were killed when they collided with the lighthouse at Pine Island, Queen Charlotte Strait, British Columbia, in April (3 birds) and May (2 birds) 1976, and April 1977 (6 birds). This mortality of non-breeding Cassin's Auklets, which occurred late in the breeding season, possibly involved subadults visiting the Pine Island colony or other nearby colonies in Queen Charlotte Strait. Body weights ranged from 169 to 204 g, within the range of weights recorded for Cassin's Auklets visiting breeding colonies elsewhere during these months. The female bias in this sample, albeit statistically significant, is unexplained.