Long-term effects of developmental conditions on health, longevity and other fitness components in humans are drawing increasing attention. In evolutionary ecology, such effects are of similar importance because of their role in the trade-off between quantity and quality of offspring. The central role of energy consumption is well documented for some long-term health effects in humans (e.g. obesity), but little is known of the long-term effects of rearing conditions on energy requirements later in life. We manipulated the rearing conditions in zebra finches (Taeniopygia guttata) using brood size manipulation and cross-fostering. It has previously been shown in this species that being reared in a large brood has negative fitness consequences, and that such effects are stronger in daughters than in sons. We show that, independent of mass, standard metabolic rate of 1-year-old birds was higher when they had been reared in a large brood, and this is to our knowledge the first demonstration of such an effect. Furthermore, the brood size effect was stronger in daughters than in sons. This suggests that metabolic efficiency may play a role in mediating the long-term fitness consequences of rearing conditions.