Daily foraging patterns of adult Double-crested Cormorants during the breeding season

We recorded the daily presence of Double-crested Cormorants (Phalacrocorax auritus) at the nesting island on Oneida Lake, New York, by monitoring the activities of 15 radio-tagged adults from July through September, 2000, using an automated data-logging receiver. A total of 24,464 acceptable detections was obtained for adult cormorants actively attempting to nest on the lake. Tagged cormorants had a bimodal dally activity pattern during the first month, with the fewest birds detected on the island at 09.00 h and 15.00 h Eastern daylight time. The pattern of activity appeared to change slightly in the second month of the study, representative of a post-breeding period for the colony, with a shift from a less synchronous pattern of departures to a greater focus on morning activity also centered around 09.30 h. These results correspond with daily observations of Great Cormorant (P. carbo) foraging activities reported for colonies in Africa and Poland. The data also support the possibility of nocturnal foraging activity, not previously reported for this species on their summer breeding grounds. No correlation was found between total number of daily detections and climatalogical factors or events.