Generational shift in spring staging site use by a long-distance migratory bird

In response to environmental change, species have been observed altering their migratory behaviours. Few studies, however, have been able to determine whether these alterations resulted from inherited, plastic, or flexible changes. Here we present a unique observation of a rapid population-level shift in migratory routes — over 300 km from Spain to Portugal — by continental black-tailed godwits Limosa limosa limosa. This shift did not result from adult godwits changing staging sites, as adult site use was highly consistent. Rather, the shift resulted from young godwits predominantly using Portugal over Spain. We found no differences in reproductive success or survival among individuals using either staging site, indicating that the shift resulted from developmental plasticity rather than natural selection. Our results therefore suggest that new migratory routes can develop within a generation and that young individuals may be the agents of such rapid changes.学界已观察到，物种会为响应环境变化而改变其迁徙行为。然而，鲜有研究能够明确此类行为改变究竟源于遗传继承、表型可塑性或是适应性灵活调整。 在此，我们报告一项独特的观测结果：大陆种群的黑尾塍鹬指名亚种（Limosa limosa limosa）出现了种群层面的迁徙路线快速转变，其迁徙范围从西班牙向葡萄牙偏移超过300公里。 此次路线转变并非由成鸟更换迁徙停歇地所致——因为成鸟对停歇地的使用具有高度一致性。恰恰相反，该转变源于幼鸟优先选择以葡萄牙而非西班牙作为停歇地。 我们发现，使用两类停歇地的个体在繁殖成功率与存活率上均无显著差异，这表明此次路线转变源于发育可塑性（developmental plasticity）而非自然选择（natural selection）。 综上，本研究结果表明，全新的迁徙路线可在单一代际内形成，而幼鸟可能正是这类快速变化的主导推动者。