Data from: The large-scale drivers of population declines in a long-distance migratory shorebird

Migratory species can travel tens of thousands of kilometers each year, spending different parts of their annual cycle in geographically distinct locations. Understanding the drivers of population change is vital for conserving migratory species, yet the challenge of collecting data over entire geographic ranges has hindered attempts to identify the processes leading to observed population changes. Here, we use remotely sensed environmental data and count data to investigate the factors driving variability in abundance in two subspecies of a long-distance migratory shorebird, the bar-tailed godwit (Limosa lapponica). We compiled a spatially and temporally explicit dataset of three environmental variables to identify the conditions experienced by each subspecies in each stage of their annual cycle (breeding, non-breeding and staging). We used a Bayesian N-mixture model to analyze 18 years of monthly count data from 21 sites across Australia and New Zealand in relation to the remote sensing datasets. We found that the abundance of one subspecies (L. l. menzbieri) in their non-breeding range was related to climate conditions in breeding grounds, and detected sustained population declines between 1995 and 2012 in both subspecies (L. l. menzbieri, -6.7% and L. l. baueri, -2.1% year-1). To investigate the possible causes of the declines, we quantified changes in habitat extent at 22 migratory staging sites in the Yellow Sea, East Asia, over a 25-year period and found -1.7% and -1.2% year-1 loss of habitat at staging sites used by L. l. menzbieri and L. l baueri, respectively. Our results highlight the need to identify environmental and anthropogenic drivers of population change across all stages of migration to allow the formulation of effective conservation strategies across entire migratory ranges.

迁徙物种每年可行进数万千米，在地理分隔的不同区域完成年度生命周期的不同阶段。明晰种群变化的驱动因子对迁徙物种保护至关重要，但在整个地理分布范围内收集数据的难题，阻碍了学界对引发观测到的种群变化的过程进行识别的尝试。本研究利用遥感环境数据与计数数据，探究长距离迁徙滨鸟斑尾塍鹬（Limosa lapponica）的两个亚种的种群丰度变异驱动因素。我们构建了包含三个环境变量的时空显式数据集，以明确两个亚种在年度生命周期各阶段（繁殖期、非繁殖期与中途停歇期）所经历的环境条件。我们采用贝叶斯N混合模型（Bayesian N-mixture model），分析了澳大利亚与新西兰境内21个监测点历时18年的月度计数数据，并结合遥感数据集开展关联分析。研究发现，其中一个亚种（L. l. menzbieri）的非繁殖区种群丰度与其繁殖地的气候条件相关，同时检测到1995年至2012年间两个亚种均出现持续种群下降：L. l. menzbieri年降幅达6.7%，L. l. baueri年降幅达2.1%。为探究种群下降的潜在成因，我们量化了东亚黄海区域22个迁徙中途停歇点在25年间的栖息地面积变化，发现L. l. menzbieri与L. l. baueri所利用的中途停歇点的栖息地年损失率分别为1.7%与1.2%。本研究结果凸显出，需在迁徙全阶段识别种群变化的环境与人为驱动因子，从而在整个迁徙分布范围内制定有效的保护策略。