| Abstract: | Body insulation is critically important for diving marine endotherms.
However,cormorants have a wettable plumage, which leads to poor insulation.
Despitethis, these birds are apparently highly successful predatorsin most
aquatic ecosystems. We studied the theoretical influenceof water temperature,
dive depth, foraging techniques, and preyavailability on the energetic costs
of diving, prey search time,daily food intake, and survival in foraging,
nonbreeding greatcormorants (Phalacrocorax carbo). Our model was
based on fieldmeasurements and on data taken from the literature. Water
temperatureand dive depth influenced diving costs drastically, with predicted
increasesof up to 250% and 258% in males and females, respectively. Changes
inwater temperature and depth conditions may lead to an increaseof daily
food intake of 500-800 g in males and 440-780 g infemales. However, the model
predicts that cormorant foragingparameters are most strongly influenced by
prey availability,so that even limited reduction in prey density makes birds
unableto balance energy needs and may thus limit their influence onprey
stocks. We discuss the ramifications of these results withregard to foraging
strategies, dispersal, population dynamics,and intraspecific competition in
this avian predator and pointout the importance of this model species for our
understandingof foraging energetics in diving endotherms. |
