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 rel ation to brood desertion in great tits. Before desertion, pairs that abando ned their broods in the second half of the nestling period had significantl y higher nestling mortality as well as lower average weight of nestlings an d entire broods. Independently of brood size, female great tits that desert ed their broods on average weighed Ig (> 5%) more than non-deserters. Compa rison of metabolic profiles revealed that deserting females were in better nutritional condition (inclined to fat deposition) than non-deserters, whic h showed symptoms of post-resorptive catabolic state, as indicated by a low er level of plasma triglycerides, very low density lipoproteins, and a high er level of free fatty acids and beta-hydroxy-butyrate. These results sugge st 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 ass ociated with age- or disease-related differences in residual reproductive v alues. Male condition was not related to brood abandonment, suggesting that desertions were primarily initiated by females.