NESTING BIOLOGY AND PREDATION OF PIGEON GUILLEMOTS IN THE QUEEN-CHARLOTTE-ISLANDS, BRITISH-COLUMBIA

The nesting biology, diet, and mortality of Pigeon Guillemots (Cepphus columba) and the effects of predation on them was investigated in Ski degate Inlet in the Queen Charlotte Islands. Their nesting population was estimated at 1000 - 1100 pairs. Pigeon Guillemots were first seen on their colonies on April 12; their mean laying and hatching dates fe ll on June 14 +/- 12.3 and July 14 +/- 11.5, respectively, and fledgin g peaked in the last week of August in 1991. The average clutch size w as 1.58 +/- 0.30 eggs; egg length and volume increased over the season . The reproductive success of Pigeon Guillemots in Skidegate Inlet was low (0.41 fledglings/pair) compared to other regions, due largely to predation. Major predators were Northwestern Crows (Corvus caurinus) a nd raccoons (Procyon lotor), an introduced species. Food shortage coul d also have been a factor in the low success, as younger chicks in two -chick broods had significantly lower weights and higher mortality tha n older siblings and single-raised chicks. Food brought to Pigeon Guil lemot chicks consisted of epibenthic fishes, mostly gunnels (Pholidae) and pricklebacks (Stichaeidae). It is recommended that Pigeon Guillem ot attendance at colonies in the Queen Charlotte Islands be monitored and the effects of raccoon predation on their reproductive success be further investigated.