Abstract
1. In many animal species, sexually mature individuals may skip breeding opportunities despite a likely negative impact on fitness. In spatio-temporally heterogeneous en-vironments, habitat selection theory predicts that individuals select habitats where fitness prospects are maximized. Individuals are attracted to high- quality habitat patches where they compete for high-quality breeding sites. Since failures in contests to secure a site may prevent individuals from breeding, we hypothesized that attrac-tion to and competition for high-quality habitats could shape breeding propensity.2. Under this hypothesis, we predicted the two following associations between breeding propensity and two key population features. (1) When mean habitat quality in the population increases in multiple patches such that availability of high- quality sites increases across the population, the resulting decrease in competition should positively affect breeding propensity. (2) When the number of individuals increases in the population, the resulting increase in competitors should negatively affect breeding propensity (negative density dependence).3. Using long-term data from kittiwakes Rissa tridactyla, we checked the prerequi-site of prediction (1), that availability of high-quality sites is positively associated with current mean habitat quality in the population (represented by breeding success). We then applied integrated population modelling to quantify annual fluctuations in population mean breeding success, breeding propensity and number of individuals by breeding status (pre- breeders, breeders, skippers and immigrants), and tested our predictions.4. Our results showed that breeding propensity acts as an important driver of population growth. As expected, breeding propensity was positively associated with preceding mean habitat quality in the population, and negatively with the number of competitors. These relationships varied depending on breeding sta-tus, which likely reflects status dependence in competitive ability.