Canham Rachel, Flemming Scott A, Hope David D, Drever Mark C
Environment and Climate Change Canada Pacific Wildlife Research Centre Delta BC Canada.
Environment and Climate Change Canada Canadian Wildlife Service Ottawa ON Canada.
Ecol Evol. 2021 Feb 28;11(6):2828-2841. doi: 10.1002/ece3.7240. eCollection 2021 Mar.
Estuaries of major rivers provide important stopover habitat for migratory birds throughout the world. These estuaries experience large amounts of freshwater inputs from spring runoff. Understanding how freshwater inputs affect food supply for migrating birds, and how birds respond to these changes will be essential for effective conservation of critical estuarine habitats. We estimated trends over time in counts of Western Sandpiper () and Pacific Dunlin () during northward migration on the Fraser River estuary, British Columbia, Canada, where shorebirds feed extensively on intertidal biofilm and invertebrates. We also examined whether counts were correlated with a suite of environmental variables related to local conditions (precipitation, temperature, wind speed and direction, solar radiation, tidal amplitude, and discharge rates from the Fraser River) during a total of 540 surveys from 1991 to 2019. Counts of Western Sandpiper declined ~54% (-2.0% per annum) over the entire study period, and 23% from 2009 to 2019 (-0.9% per annum). Counts of Pacific Dunlin did not show a statistically significant change over the study period. Counts of shorebirds were lower when discharge from the Fraser River was high, which we propose results from a complex interaction between the abrupt changes in salinity and the estuarine food web related to the quantity or quality of intertidal biofilm. Counts were also higher when tidal amplitude was lower (neap tides), potentially related to longer exposure times of the mudflats than during spring tides. Effects of wind are likely related to birds delaying departure from the stopover site during unfavorable wind conditions. The negative trend in migrating Western Sandpipers is consistent with declines in nonbreeding areas as observed in Christmas Bird Counts. Understanding causes of population change in migratory shorebirds highlights the need for research on mechanistic pathways in which freshwater inputs affect food resources at estuarine stopovers.
主要河流的河口为全球候鸟提供了重要的中途停歇栖息地。这些河口会因春季径流而有大量淡水注入。了解淡水输入如何影响候鸟的食物供应，以及鸟类如何应对这些变化，对于有效保护关键河口栖息地至关重要。我们估计了在加拿大不列颠哥伦比亚省弗雷泽河河口北迁期间西部滨鹬（）和黑腹滨鹬（）数量随时间的变化趋势，在这里滨鸟大量取食潮间带生物膜和无脊椎动物。我们还研究了在1991年至2019年共540次调查期间，数量是否与一系列与当地状况相关的环境变量（降水量、温度、风速和风向、太阳辐射、潮汐幅度以及弗雷泽河的流量）相关。在整个研究期间，西部滨鹬的数量下降了约54%（每年下降2.0%），从2009年到2019年下降了23%（每年下降0.9%）。在研究期间，黑腹滨鹬的数量没有显示出统计学上的显著变化。当弗雷泽河的流量较高时，滨鸟数量较低，我们认为这是盐度突然变化与与潮间带生物膜数量或质量相关的河口食物网之间复杂相互作用的结果。当潮汐幅度较低（小潮）时，数量也较高，这可能与滩涂比大潮期间更长的暴露时间有关。风的影响可能与鸟类在不利风况下推迟离开中途停歇地有关。西部滨鹬迁徙数量的负趋势与圣诞鸟类统计中观察到的非繁殖地数量下降一致。了解迁徙滨鸟种群变化的原因凸显了对淡水输入影响河口中途停歇地食物资源的机制途径进行研究的必要性。
