Wintering areas predict age-related breeding phenology in a migratory passerine bird

Understanding connections between breeding, stopover and wintering grounds for long-distance migratory birds can provide important insight into factors influencing demography and the strength of carry-over effects among various periods of the annual cycle. Using previously described, multi-isotope (δ13C, δ15N, δ2H) feather isoscapes for Africa, we identified the most probable wintering areas for house martins (Delichon urbica) breeding at Badajoz in southwestern Spain. We identified two most-probable wintering areas differing in latitude in West Africa. We found that the probability to winter in the northern region was related to age and sex of individuals. Specifically, experienced males (i.e., two years or older) winter in the northern area with a greater probability than experienced females, whereas first-year females winter in the northern area with a greater probability than first-year males. In addition, wintering area was correlated with breeding phenology, with individuals wintering in the northern area initiating their clutches earlier than those wintering in the southern area. For birds wintering in the northern area, there was no relationship between age and clutch initiation date. In contrast, young birds wintering in the southern area initiated their clutches earlier than experienced birds wintering in this area. There was no significant correlation between wintering area and clutch size or the number of fledglings produced. We hypothesize that the relationship among social status, population density and winter habitat quality should be the most important driver of the carry-over effect we found for this population

解析长途迁徙鸟类繁殖地、中途停歇地与越冬地之间的关联，可为揭示影响种群动态的因素以及年度周期不同阶段间的携带效应（carry-over effects）强度提供重要见解。本研究依托此前已发表的非洲区域多同位素（δ¹³C、δ¹⁵N、δ²H）羽毛同位素等值线图（feather isoscapes），对西班牙西南部巴达霍斯地区繁殖的白腹毛脚燕（Delichon urbica）的最可能越冬地进行了识别。研究识别出西非地区两个纬度梯度不同的最可能越冬区域。研究发现，个体在北部区域越冬的概率与年龄和性别相关。具体而言，成年雄鸟（2龄及以上个体）在北部区域越冬的概率高于成年雌鸟；而当年生雌鸟在北部区域越冬的概率则高于当年生雄鸟。此外，越冬区域与繁殖物候存在关联：在北部区域越冬的个体，其产卵始期早于在南部区域越冬的个体。对于在北部区域越冬的个体，年龄与产卵始期并无显著关联。与之相反，在南部区域越冬的当年生个体，其产卵始期早于该区域内的成年个体。越冬区域与窝卵数或出飞幼鸟数量无显著相关性。本研究提出假说：社会地位、种群密度与越冬栖息地质量之间的关联，应为该种群观测到的携带效应的核心驱动因素。