Effects of the doubly labelled water procedure on great tits Parus major feeding young

Capsule. Female Great Tit Parus major feeding rate behaviour was highly variable between individuals, but no effect of the doubly labelled water (DLW) procedure on female visit rate was detected, whereas visit rates by males, which were neither trapped or manipulated, increased following trapping and manipulation of their partners. Aims. To test the assumption that the subject’s behaviour is normal during the measurement period when using DLW to measure energy expenditure. Methods. Visits to the nest box by parents feeding young were counted separately for females and males on the day before and the day after the female only was trapped to measure her energy expenditure using DLW. Visit rates were also counted for control pairs. Results. Female visit rates did not differ before and after manipulation, or between experimental and control pairs, but bird behaviour was highly variable between individuals. In contrast, the visit rates of both experimental and control males, which were not trapped, increased on the second day. Conclusion. The results for female behaviour supported the assumption of normality, but a small subset of particular individuals may be prone to adverse reactions. The response of the males may have been a reaction to disturbance at the nest.