ИСТИНА

Resting metabolic rate (RMR) of Pied Flycatcher fledglings was measured in Moscow region (2000-2005, 953 chicks from 362 broods). Our aim was to compare RMR in broods of different size and different rate of chicks' death from starvation. Fledglings' RMR was negatively related to final brood size only in "unsuccessful" broods (in which some nestlings starved to death), but not in "successful" broods. The effect of RMR increase due to wide range of brood size reduction occurred only in nests with the most common clutch sizes (5-7 eggs), but not in nests with extra-large or small clutches. As a consequence, chicks from "unsuccessful" broods had higher mean RMR than chicks from "successful" broods. Growth rates of chicks during last week of their stay in a nest were the same in "successful" and "unsuccessful" broods. Therefore higher RMR of fledglings in "unsuccessful" broods could result from their superiority in such component of RMR as basal metabolic rate (BMR). Three possible explanations of increased RMR of fledglings from "unsuccessful" broods were discussed in terms of within-brood competition: 1) Mortality occurs mainly in broods with high energy requirements of chicks; 2) Within brood, chicks with higher RMR have better chances to survive; 3) RMR of survived chicks increased in response to weakening of within-brood competition.