Age-related breeding success in little penguins: A result of selection and ontogenetic changes in foraging and phenology

Reproductive performance typically improves with age, reaching a plateau at middle age and subsequently declining in older age classes (senescing individuals). Three potential non-exclusive mechanisms can explain the improvement in reproductive performance with age: (1) selection (poor quality individuals are removed from the population with increasing age), (2) constraint (individual efficiency increases through experience) and (3) restraint (reproductive investment increases with age as the residual reproductive value decreases). While all three mechanisms received strong empirical support, few studies have aimed at teasing apart those hypotheses and understanding their underlying functioning. In little penguins (Eudyptula minor), we used a 19-year longitudinal dataset on breeding and foraging of more than 450 individuals to investigate the effect of age on breeding success. We separated within- from among-individual age-effects using state-of-the-art statistical methods (within-subje...