Do great tits (Parus major) starve to reproduce?

To test whether nest abandonment is associated with parental health state, reproductive parameters and parental condition indices were examined in relation to brood desertion in great tits. Before desertion, pairs that abandoned their broods in the second half of the nestling period had significantly higher nestling mortality as well as lower average weight of nestlings and entire broods. Independently of brood size, female great tits that deserted their broods on average weighed Ig (> 5%) more than non-deserters. Comparison of metabolic profiles revealed that deserting females were in better nutritional condition (inclined to fat deposition) than non-deserters, which showed symptoms of post-resorptive catabolic state, as indicated by a lower level of plasma triglycerides, very low density lipoproteins, and a higher level of free fatty acids and beta-hydroxy-butyrate. These results suggest that desertion can be regarded as a reproductive restraint and that non-deserting females invested at least some of their maintenance resources on brood rearing. We found no evidence that desertion or non-desertion was associated with age- or disease-related differences in residual reproductive values. Male condition was not related to brood abandonment, suggesting that desertions were primarily initiated by females.