Reproductive performance of resident and migrant males, females and pairs in a partially migratory bird

1. Quantifying among-individual variation in life-history strategies, and associated variation in reproductive performance and resulting demographic structure, is key to understanding and predicting population dynamics and life-history evolution. Partial migration, where populations comprise a mixture of resident and seasonally-migrant individuals, constitutes a dimension of life-history variation that could be associated with substantial variation in reproductive performance. However, such variation has rarely been quantified due to the challenge of measuring reproduction and migration across a sufficient number of seasonally-mobile males and females. 2. We used intensive winter (non-breeding season) resightings of colour-ringed adult European shags (Phalacrocorax aristotelis) from a known breeding colony to identify resident and migrant individuals. We tested whether two aspects of annual reproductive performance, brood hatch date and breeding success, differed between resident and mi...