SUBCUTANEOUS FAT ACCUMULATION IN NORWEGIAN OWLS AND RAPTORS

The mean subcutaneous fat deposition (MFS) found in dead diurnal rapto rs and owls collected in Norway in 1987-92 was compared to detect poss ible overall and intra- and interspecific seasonal differences. In gen eral, the relative fat deposition rate was correlated with body size ( P < 0.001), and was highest in winter (P = 0.01) and in females (P = 0 .02). After correcting for the size effect, species-specific differenc es were still present (P = 0.000), but the effect of sex disappeared ( P = 0.34). We propose that the relative rate of fat deposition in nort hern Palaearctic owls and raptors reflects adaptations to resist starv ation balanced against the demands for high agility and low flying cos ts. This trade-off probably varies between breeding and non-breeding s easons, sexes, and species with different migratory and hunting habits .