Diving Behavior in Pelagic Cormorants in Summer near San Juan Island, WA

Abstract

This study, conducted on San Juan Island, Washington during late summer, assessed variation in diving behavior of pelagic cormorants relative to time of day and tidal currents. Mean dive lengths did not differ significantly between morning and afternoon periods. However, dive lengths were longer during ebb versus flood tides and dive lengths also increased with the speed of water currents where diving occurred. To explore the possibility of physiological adaptations to low oxygen availability, the length of rest periods following dives was measured to see if pelagic cormorants displayed dive time to rest time rations that deviated from the a 1:1 ratio typical of aerobic diving. Because they do not strictly adhere to the predicted 1:1 ratio of aerobic dive time to rest time, pelagic cormorants likely have additional adaptations that allow them to cope with reduced access to oxygen.