Social and demographic factors of varying the basal metabolic rate in wintering groups of the great tit, Parus major

The recently developed model of avian energetics (Gavrilov, 1997) predicts that the basal metabolic rate (BMR) of an individual bird reflects its long -term working capacity and competitive potential. Relations between BMR and adaptation of birds are poorly known. The paper deals with observing great tits wintering in optimal habitats (Moscow district) and estimating their flocking and territorial behaviour affecting their future reproductive succ ess, The BMR was determined by the level of consuming oxygen at night. Youn g males had the higher BMR (calculated per mass unit) than old ones. This i ndex was also higher in wintering flock members than in transient birds. Th e BMR of territorial bird males exceeded that of non-territorial ones. Such a trend was pronounced stronger in young birds from the very beginning of winter. BMR correlated positively with indices of social behaviour only in new members of the basic flock. The preceding residence time influenced inv ersely the BMR in juveniles and adults. A high BMR was characteristic of yo ung birds for the first month of their joining the flock, then its value de creased. The BMR in old males increased with increasing the time spent in t he flock area. According to the model, an increase of the BMR in an individ ual bird with raising its flock and territorial status appears to reflect a n additional energy cost of the batter social position. In developing socia l relations, new members of the population (primarily. young birds) have to shift to the high power regime for compensation of lack of social experien ce.