Repeatability of basal metabolism in breeding female kittiwakes Rissa tridactyla

We studied kittiwakes (Rissa tridactyla) breeding near Ny-Alesund (79 degre es N, 12 degrees E) on Svalbard. In 1997, the basal metabolic rates (BMRs) of 17 breeding females were measured during the incubation and chick-rearin g periods. The mean body mass of the kittiwakes decreased significantly (by 10%) between the incubation and chick-rearing periods. At the same time, b oth the whole-body and mass-specific BMRs decreased significantly. There wa s a positive and significant relationship between the BMR residuals from th e incubation period and those from the chick-rearing period. Thus, the BMR of incubating female kittiwakes is a significant predictor of their BMR dur ing the chick-rearing period. New BMR data were collected in 1998 from ten of these females, measured around the chick-hatching date. Repeatability va lues were calculated using either (i) the data for eight individuals for wh ich three BMR measurements existed, or (ii) all the data from both years, y ielding significant repeatabilities of 0.52 and 0.35, respectively. These v alues indicate that between 48 and 65% of the observed variation in BMR is due to intraindividual variability, while between-individual variability ac counts 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.