Data from: Migration tendency delays distributional response to differential survival prospects along a flyway

When populations grow or decline, habitat selection may change due to local density-dependent processes, such as site dependence and interference. In seasonally migrating animals, nonbreeding distributions may be determined through these mechanisms of density dependence, which we examine here at a hemispheric scale for a long-distance migrating bird. Using summer and winter resightings of 2,095 Eurasian spoonbills Platalea leucorodia leucorodia that were ringed in the Netherlands during 16 years of fast population growth, we show that neither site dependence nor interference fully explains their patterns of survival and winter distribution. Within their three main wintering areas, annual survival decreased with an increase in population size. While survival was consistently higher in the two European wintering areas (France, Iberia), most spoonbills migrated onward to winter in west Africa. The number of birds wintering in Europe increased, but not enough to maximize annual survival. We conclude that a constraint of tradition (their “migration tendency”) inhibits birds from changing their migratory habits. We pose that this phenomenon may similarly constrain other migratory populations from rapidly responding to large-scale climate- and/or human-driven habitat changes at their wintering grounds.

当种群发生增减时，栖息地选择可能因局域密度制约过程（如位点依赖与干扰竞争）发生改变。对于季节性迁徙动物而言，其非繁殖期分布或由这类密度制约机制决定；本文便在半球尺度下，针对一种长途迁徙鸟类展开相关研究。我们利用16年种群快速增长期内，于荷兰环志的2095只白琵鹭指名亚种（Platalea leucorodia leucorodia）的夏季与冬季重见数据，研究发现位点依赖与干扰竞争均无法完全解释它们的存活模式与越冬分布特征。在其三个主要越冬区内，年存活率随种群规模扩大而下降。尽管两处欧洲越冬区（法国、伊比利亚半岛）的存活率始终更高，但多数琵鹭仍会继续迁徙至西非越冬。欧洲越冬的鸟类数量有所增加，但增幅未达到使年存活率最大化的水平。我们由此得出结论，‘迁徙倾向’这一传统习性约束，阻碍了鸟类改变自身迁徙行为。我们推测，这一现象可能同样会制约其他迁徙种群，使其无法快速响应越冬地因气候或人类活动驱动的大规模栖息地变化。