Data from: Why migrate during the day: a comparative analysis of North American birds

Migration can take place primarily during the day, or at night, or during both depending on the species. Why the timing of migration varies among species has been the object of much research but the underlying ecological processes are still unclear. Proximally, migration timing may be influenced by the timing of other activities or may be more prevalent in species that migrate over long distances. Adaptive scenarios emphasize the reduction in flight costs at night especially in smaller species and the advantages of travelling in groups during the day to locate staging sites more efficiently. I used phylogenetic independent contrasts to examine these hypotheses in all North American nesting birds. I uncovered 24 evolutionary transitions in migration timing, most of which involved a switch from nocturnal to diurnal migration. Few of these transitions involved a concomitant change in the timing of foraging habits or migration distance. However, species in diurnal clades were larger, travelled in larger flocks and were generally more sociable than their nocturnal counterparts. The results support the hypotheses that a reduction in flight costs and the ability to pool information from companions are associated with migration timing in North American bird species.鸟类的迁徙主要可在日间、夜间或昼夜兼具进行，具体取决于物种种类。不同物种迁徙时间存在差异的原因一直是诸多研究的关注焦点，但其背后的核心生态过程仍未明晰。从近因层面来看，迁徙时间可能会受到其他活动时间的影响，也可能在长距离迁徙物种中更为普遍。适应性假说着重强调了夜间飞行可降低飞行成本这一优势，尤其针对体型较小的物种；以及日间结伴迁徙能够更高效地定位中途停歇地的益处。本研究采用系统发育独立对比（phylogenetic independent contrasts）方法，针对北美所有筑巢鸟类检验了上述假说。研究共发现24次迁徙时间的演化转变，其中绝大多数均涉及从夜行性迁徙向昼行性迁徙的转换。此类转变中，仅有极少数伴随取食习性时间或迁徙距离的同步变化。不过，相较于夜行性迁徙鸟类，昼行性迁徙类群的体型更大、鸟群规模更大，且整体社交性更强。研究结果支持如下假说：飞行成本的降低，以及从同伴处整合信息的能力，与北美鸟类的迁徙时间模式存在关联。