Assessing the effect of male age on breeding performance in an Alpine population of Northern Wheatears Oenanthe oenanthe

Capsule: In many bird species, differences in breeding parameters are often reported between (inexperienced) yearlings and adults (with previous breeding experience), likely due to increased foraging and chick rearing abilities in older, more experienced, individuals. Aims: We aimed to assess the effect of male age on breeding parameters in an Alpine population of Northern Wheatears. Methods: We compared several performance parameters (nesting habitat, lay date, daily failure rates, nest survival and nestling mass) between yearling (inexperienced) and adult (experienced) Northern Wheatears in a population in the western Italian Alps. Results: There was no statistically significant effect of male age (i.e. yearlings vs older birds) on breeding success, territory quality or breeding phenology, but there was a weak trend of a higher nest survival among adults. Conclusion: Unpredictable weather and overall high food abundance at higher elevations during the breeding period may reduce any difference in nest survival or nestling mass between age classes, even if older birds have better foraging capabilities. Compared to lowland studies, the results suggest that our Alpine population of Northern Wheatears differed in the constraints acting on breeding success and phenology: harsh and unpredictable environmental conditions on arrival and superabundant food availability for nestlings likely reduce age differences in breeding success, territory quality and phenology. Biases due to potential unrepresentative sampling of age groups must be more fully assessed to further explore these hypotheses.