Data from: 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 migrant males, females and breeding pairs observed across three consecutive winters and breeding seasons. 3. The sex ratios of observed resident and migrant shags did not significantly differ from each other or from 1:1, suggesting that both sexes are partially migratory and that migration was not sex-biased across surveyed areas. 4. Individual resident males and females hatched their broods 6 days earlier and fledged 0.2 more chicks per year than migrant males and females on average. Resident individuals of both sexes therefore had higher breeding success than migrants. 5. Hatch date and breeding success also varied with a pair’s joint migratory strategy such that resident-resident pairs hatched their broods 12 days earlier than migrant-migrant pairs, and fledged 0.7 more chicks per year on average. However, there was no evidence of assortative pairing with respect to migratory strategy: observed frequencies of migrant-migrant and resident-resident pairs did not differ from those expected given random pairing. 6. These data demonstrate substantial variation in two key aspects of reproductive performance associated with the migratory strategies of males, females and breeding pairs within a partially migratory population. These patterns could reflect direct and/or indirect mechanisms, but imply that individual variation in migratory strategy, and variation in pairing among residents and migrants, could influence selection on migration and drive complex population and evolutionary dynamics.1. 量化个体间生活史策略（life-history strategies）的变异，以及伴随的繁殖表现变异与由此形成的种群结构变异，是理解与预测种群动态（population dynamics）和生活史演化（life-history evolution）的核心前提。部分迁徙（partial migration）指种群由留居个体与季节性迁徙个体混合构成，是生活史变异的重要维度，且可能与繁殖表现的显著差异相关联。然而，由于难以对足够数量的季节性移动雌雄个体同步开展繁殖与迁徙相关测量，这类变异迄今鲜有量化研究。 2. 本研究针对某已知繁殖种群的彩色环志成年欧洲鸬鹚（Phalacrocorax aristotelis）开展高强度冬季（非繁殖季）重见调查，以此区分留居个体与迁徙个体。我们针对连续3个冬季与繁殖季内观测到的留居与迁徙雄性、雌性个体及繁殖对，检验了年度繁殖表现的两个核心维度——窝卵孵化日期与繁殖成功率——是否在两类群体间存在差异。 3. 观测到的留居与迁徙鸬鹚的性比（sex ratio）均无显著组间差异，且均未偏离1:1的平衡比例，这表明雌雄两性均存在部分迁徙现象，且研究区域内的迁徙行为无性别偏向。 4. 平均而言，留居的雄性与雌性个体的窝卵孵化日期较迁徙个体早6天，年均多育活0.2只雏鸟。因此，两性留居个体的繁殖成功率均高于迁徙个体。 5. 孵化日期与繁殖成功率同样随繁殖对的联合迁徙策略发生变化：留居-留居繁殖对的窝卵孵化日期较迁徙-迁徙繁殖对早12天，年均多育活0.7只雏鸟。然而，未发现基于迁徙策略的选型配对（assortative pairing）现象：观测到的迁徙-迁徙与留居-留居繁殖对的频率，与随机配对下的预期频率无显著差异。 6. 本数据集证实了部分迁徙种群中，雌雄个体与繁殖对的迁徙策略与繁殖表现的两个核心维度存在显著关联变异。这些模式可能反映了直接或间接的作用机制，但也表明个体迁徙策略的变异，以及留居者与迁徙者之间的配对变异，可能会影响迁徙相关的选择压力，并推动复杂的种群动态与演化过程。