Study of optimal foraging of diving seabirds with micro-time scale measurements of accceleration

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Seabirds are known to dive deeper and longer than marine mammals after body mass is adjusted. Many laboratory studies have been carried out to understand the physiological and behavioural mechanisms of this high diving ability. Since its underwater foraging has to be achieved under limitation of with the limited amount of oxygen store, it is also a good material of the study of optimal foraging. Empirical study in the wild, however, has bee insufficient because of the difficulties collecting data of energetic cost and food intake. We measured detail of diving bahaviour and prey pursuit in deep diving seabirds in the wild to examine the cost and benefit of diving. Our specific aim is to understand the mechanism of high diving ability and prey intake when the birds face with the buoyancy and the drag in the water. To estimate biomechanical cost of wing or foot stroke, habitat utilization, and prey capture, we attached acceleration recording data-loggers and camera-loggers on back of alci … More ds and a penguin, and shags. 1) We proposed a hypothesis that shags balance the cost of increasing stroke rate and the benefit of the reduction of transit time by increasing swim speed. We found that 2) specialist divers (seabirds and marine mammals) decrease the frequency of stroke with the power function of body mass (0.3) presumably to keep a range of swim speed (2m/s), and 3) flying-diving seabirds, however, had higher and lower stroke frequency in the air and water, respectively, than expected; indicating a compensated stroke pattern suitable for flying and swimming. Further, we proposed new techniques to estimate 4) food intake during a each foraging bout by measuring wing stroke frequency at short time scale (<10min) during the flight period between diving bouts and 5) micro habitat use and prey pursuit by taking image data while foraging during bottom phase. To understand the effects of marine environmental change on fine scale adjustment of foraging behaviour, we studied diving and foraging behaviour of guillemots in the Bering Sea. We found that 1) guillemots changed dive depth and foraging water masses in relation to the change of thermocline and resulting vertical distribution of prey, 2) parents forage easily collected small prey, krill and 0-year-pollack for themselves but dove deep to capture large fish and 1+ Pollack to increase provisioning rate. Less