Data from: Long-term changes in the seasonal timing of landbird migration on the Pacific Flyway

The seasonal phenology of latitudinal movements is one of the key life-history traits of migratory birds. We used quantile regression to examine long-term changes in the timing of spring and autumn migration in 5 species of migratory passerine birds captured at a banding station in northern California, USA, over a 22 yr period from 1987 to 2008. Our 5 study species included 3 short-distance migrants, Pacific-slope Flycatcher (Empidonax difficilis), Orange-crowned Warbler (Oreothlypis celata), and Wilson's Warbler (Cardellina pusilla); and 2 long-distance migrants, Swainson's Thrush (Catharus ustulatus) and Yellow Warbler (Setophaga petechia). Median timing of migration advanced in spring for 2 of the 5 species (−2.5 days decade−1) but was delayed during autumn migration for 3 of the species (+2.9 days decade−1). The duration of the migration period also became compressed in some species but more protracted in others. We tested whether annual variation in migration timing was related to 3 indices of regional climatic conditions: the Pacific–North American index, multivariate El Niño–Southern Oscillation index, and North Atlantic Oscillation index. Climate indices explained relatively little of the variation in migration timing (r2 < 0.35), but advances in spring migration and delays in autumn migration were associated with warm, wet conditions during positive phases of the climate indices. The strongest effects of climatic conditions on migration timing were found among short-distance migrants, with the largest changes in timing due to variation in the El Niño–Southern Oscillation and Pacific–North American indices. Linkages between the timing of movements and climatic conditions indicate that passerine birds on the Pacific coast exhibit phenotypic plasticity in their migration timing, but future studies based on experimental methods are needed to test alternative ecological mechanisms.

纬度迁移的季节物候特征是候鸟核心生活史性状之一。我们采用分位数回归（quantile regression）方法，针对1987至2008年这22年间，在美国加利福尼亚州北部一处环志站捕获的5种迁徙雀形目鸟类，探究其春季与秋季迁徙时间的长期变化趋势。本次研究的5个物种包括3种短距离迁徙鸟类：太平洋坡霸鹟（Pacific-slope Flycatcher，Empidonax difficilis）、橙顶林莺（Orange-crowned Warbler，Oreothlypis celata）以及威尔逊鸣莺（Wilson's Warbler，Cardellina pusilla）；以及2种长距离迁徙鸟类：斯温氏夜鸫（Swainson's Thrush，Catharus ustulatus）和黄林莺（Yellow Warbler，Setophaga petechia）。春季迁徙中位时间在2个物种中呈提前趋势（每十年提前2.5天），而秋季迁徙中位时间在3个物种中呈延后趋势（每十年延后2.9天）。部分物种的迁徙周期时长有所压缩，另一些物种的迁徙周期则更为延长。我们检验了迁徙时间的年际变异是否与3种区域气候指数相关：太平洋-北美指数（Pacific–North American index）、多变量厄尔尼诺-南方涛动指数（multivariate El Niño–Southern Oscillation index）以及北大西洋涛动指数（North Atlantic Oscillation index）。气候指数仅能解释较小比例的迁徙时间变异（决定系数r² < 0.35），但春季迁徙提前与秋季迁徙延后均与气候指数正相位期间的暖湿气候条件存在关联。气候条件对迁徙时间的最强影响出现在短距离迁徙鸟类类群中，其中厄尔尼诺-南方涛动指数与太平洋-北美指数的变异所带来的迁徙时间变化幅度最大。迁徙时间与气候条件之间的关联表明，太平洋沿岸的雀形目鸟类在迁徙时间上存在表型可塑性，但未来仍需开展基于实验方法的研究，以验证其他潜在的生态学机制。