ENERGY-REQUIREMENTS OF BREEDING GREAT CORMORANTS PHALACROCORAX-CARBO-SINENSIS

Cormorants and humans are purported to compete for fish resources. Recent increases in cormorant populations in western Europe have led to new conflicts between fishermen and nature conservationists, a situation which has stimulated research into the food requirements of these seabirds. However, most dietary studies are based on stomach content or pellet analysis. Both these methods are biased. We used a time-budget model to calculate the energy requirements of great cormorants Phalacrocorax carbo sinensis breeding in Schleswig-Holstein, Germany. The time budgets of the birds were recorded for different breeding phases and the energetic costs of the different activities determined through respirometric measurements or by using values derived from the literature. The food requirements of great cormorants during incubation were calculated to be 238 g adult(-1) d(-1). These requirements rise to 316 g d(-1) during the rearing of young chicks and to 588 g d(-1) during rearing of downy chicks. Human disturbance causing great cormorants to fly off their nests entails an additional consumption of 23 g fish per bird or ca 23 kg per disturbance event for a typical colony.