Repeatability of basal metabolism in breeding female kittiwakes Rissa tridactyla

We studied kittiwakes (Rissa tridactyla) breeding near Ny-Alesund (79 degrees N, 12 degrees E) on Svalbard. In 1997, the basal metabolic rates (BMRs) of 17 breeding females were measured during the incubation and chick-rearing periods. The mean body mass of the kittiwakes decreased significantly (by 10%) between the incubation and chick-rearing periods. At the same time, both the whole-body and mass-specific BMRs decreased significantly. There was a positive and significant relationship between the BMR residuals from the incubation period and those from the chick-rearing period. Thus, the BMR of incubating female kittiwakes is a significant predictor of their BMR during the chick-rearing period. New BMR data were collected in 1998 from ten of these females, measured around the chick-hatching date. Repeatability values were calculated using either (i) the data for eight individuals for which three BMR measurements existed, or (ii) all the data from both years, yielding significant repeatabilities of 0.52 and 0.35, respectively. These values indicate that between 48 and 65% of the observed variation in BMR is due to intraindividual variability, while between-individual variability accounts for 35-52% of the variation in the BMR. This is the first report of a significant repeatability of the BMR of an endothermic organism across an elapsed time of more than one day.