Basal metabolic rate (BMR) is a physiological trait believed to show adaptational changes. Few studies have tested whether BMR shows stable between-individual variations. Repeatability indicates that the trait might be heritable and therefore a possible target for natural selection. We tested whether BMR was repeatable over a considerable time of the lifespan of a small passerine bird: the zebra finch Taeniopygia guttata. BMR was measured six times over a 2.5 year period in captive zebra

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... . BMR residuals showed significant repeatabilities over a short (1.5 months) and a long (2.5 years) period for each sex as well as for both sexes pooled. In contrast to earlier studies on metabolism, our calculated repeatability (R) did not change significantly from the short to the long period in either males (R from 0.501 to 0.465), females (R from 0.413 to 0.522) or the pooled data (R from 0.571 to 0.567). Our results show that there are consistent betweenindividual variations in BMR on which natural selection can work, provided that this trait is heritable.