Résumé
Bird nests function to protect parents, eggs or offspring against fluctuations in the environment. In Blue Tits (Cyanistes caeruleus) producing first or replacement clutches, we examined relationships between nest height (a measure of nest size) and several parameters of breeding performance that are often quantified in long-term avian field studies. We artificially increased the cost of reproduction in randomly selected females by removing the whole first clutch and nest material after about 5 days of incubation. This experiment resulted in replacement nests. Experimentally increasing the range of breeding conditions across females, we expected to have more power to detect a positive correlation between nest height and breeding success. However, we found that nest height was not significantly related to any of the breeding traits investigated (clutch size, number of hatchlings, number of fledglings, hatching success, fledging success, chick mass), after controlling for factors frequently investigated in long-term monitoring programs and known to influence breeding performance (female age, year, clutch type as a proxy of egg-laying date). We conclude that the identification of the exact underlying mechanisms causing relationships between nest characteristics and breeding performance will require more experimental study and the exploitation of larger datasets, both within and across avian model systems.