Virginia marsh songbird rope-drag data – winter 2014

Bird species that are restricted to tidal marshes during one or all of their life stages are under increasing pressure from sea-level rise. To date, most of the research focused on this group has been conducted during the breeding season despite the fact that more than half of the annual cycle is spent on wintering grounds and the high likelihood that the winter period is the most critical time for adult survival. We used a double-pass rope-drag technique to estimate the winter abundance of sharp-tailed sparrows (Ammospiza nelson and A. caudacutus collectively), seaside sparrows (A. maritimus) and marsh wrens (Cistothorus palustris) within tidal marshes of Virginia along 102 60×250 m transects between January and March 2014. We used the first pass to remove birds from the transect and the second pass was used to estimate detection probabilities. The technique was highly effective producing detection rates of 98% for sharp-tailed sparrows, 95% for seaside sparrows, and 91% for marsh wren..., We used double-pass rope-drag transects to survey sparrows and wrens within marsh sites. Transects were 60m wide and their length varied from 200–250 m depending on the available space and placement within the marsh patch. The 60m rope (0.635 cm diameter) was weighted in the middle by two plastic containers filled with stones to create additional vegetation disturbance. A transect was surveyed at approx. 0.8 m/s-1 by three people where two were stationed on either end of the rope and the third walked <5 m behind the center of the rope. The third observer mapped the transect tracks to ensure that the survey was performed in a straight line. Once the entire transect length was surveyed (first pass) the observers immediately reversed direction to pass over the same area a second time (second pass) following the GPS track and observer footprints to ensure the exact same path was followed on the return pass. When birds were flushed, we recorded whether the bird landed within or outside th...,在一个或全部生命阶段中仅栖息于潮汐沼泽的鸟类正面临着海平面上升带来的日益加剧的生存压力。迄今为止，针对该类群的多数研究均集中于繁殖季，尽管鸟类全年超过一半的周期都在越冬地度过，且冬季极有可能是成鸟存活的关键时期。2014年1月至3月期间，我们沿弗吉尼亚州潮汐沼泽内的102条60×250米样线，采用双程拖绳法（double-pass rope-drag technique）估算尖尾沙鹀（Ammospiza nelson与A. caudacutus合并统计）、海滨沙鹀（A. maritimus）以及沼泽鹪鹩（Cistothorus palustris）的冬季种群数量。第一次拖行用于驱赶样线上的鸟类，第二次拖行则用于估算检测概率。该方法效果极佳，尖尾沙鹀的检测率达98%，海滨沙鹀达95%，沼泽鹪鹩达91%……我们采用双程拖绳样线法对沼泽生境内的沙鹀与鹪鹩开展调查。样线宽度为60米，长度则根据沼泽斑块内的可用空间与布设位置在200至250米之间调整。所用60米长的绳索（直径0.635厘米）在中部配有两个装满石块的塑料容器，以增强对植被的扰动。三名调查人员以约0.8米每秒的速度开展样线调查：两人分别站在绳索两端，第三人在绳索中心后方小于5米处行进。第三位观察员会记录样线轨迹，以确保调查沿直线进行。完成整条样线的首次拖行（第一程）后，调查人员立即沿GPS轨迹与步行足迹折返，对同一区域进行第二次拖行（第二程），以确保返程路径与首次完全一致。当鸟类被惊飞时，我们会记录该鸟类是落在样线内还是样线外……