Nocturnal Foraging in the American White Pelican

Nocturnal foraging was examined in American White Pelicans (Pelecanus erythrorhynchos) at the Dauphin River, about 50 km from a breeding colony on Lake Winnipeg, Manitoba, Canada. From two to three times as many pelicans foraged at night as in the daytime, with foraging flocks being larger at night. In contrast, more pelicans were present at adjacent loafing sites during the day. Capture rates were highest for flocks of up to 100 foragers in the daytime, but showed no relationship to flock size at night. Rates of bill dipping and mean duration of dips were significantly greater at night, but capture rates were significantly lower. Lower capture rates at night were to some extent offset by the capture of more large fish, probably because they were more accessible at that time. Most of the day-night differences in capture efficiency appeared to be due to lower visual sensitivity of pelicans at night.