COLONY ATTENDANCE OF PIGEON GUILLEMOTS AS RELATED TO TIDE HEIGHT AND TIME OF DAY

The attendance of Pigeon Guillemots (Cepphus columba) at three colonie s in Skidegate Inlet, Queen Charlotte Islands, British Columbia was in vestigated according to time of day and tide level during May - June 1 990 and 1991. Guillemot attendance in all three colonies was correlate d most strongly with tide height, but also with time after sunrise and tide direction. An analysis of colony attendance on Mandarte Island, British Columbia, however, found time after sunrise to be the only sig nificant factor influencing attendance. The maximal tide range at Skid egate Inlet, 7.8 m, compared to only 3.8 m at Mandarte Island, was lik ely responsible for the patterns observed. The optimal time to determi ne nesting populations of Pigeon Guillemots is at high tide in the mor ning.