Data from: Estimating abundance of the federally endangered Mitchell’s satyr butterfly using hierarchical distance sampling

1. Estimates of animal abundance are essential to conservation biology and are sorely lacking for many endangered species in the United States of America. This lack of knowledge may disproportionately affect butterflies in the USA, which form the largest group of federally protected insects (20 of 62 species). 2. The Mitchell’s satyr butterfly, Neonympha mitchellii mitchellii, is a federally endangered species found at 18 highly isolated sites in the Eastern USA. Currently, surveys are conducted by meandering through habitat and recording the number of butterflies observed. These surveys are efficient in terms of staffing and time, but the data from these surveys cannot be used to estimate abundance. Mark release recapture surveys generate estimates of demographic parameters and have been conducted, albeit infrequently, and require high staffing levels and weeks of fieldwork to generate estimates with reasonable error. 3. I employed hierarchical distance sampling along line transects to estimate N. m. mitchellii abundance at one site in lower Michigan, USA. This method requires one observer to traverse a series of transects at a walking pace and record the number of butterflies observed and their perpendicular distance to the transect line. My results suggest that this method is as cost efficient as meander surveys but generates reasonable estimates of butterfly abundance.

1. 动物丰度估算对保护生物学至关重要，但美国诸多濒危物种的此类数据仍极度匮乏。这一认知缺口对美国蝴蝶的影响尤为凸显——全美受联邦保护的昆虫类群中，蝴蝶为规模最大的类群，62种受保护昆虫里有20种为蝴蝶。
2. 米切尔眼蝶（Neonympha mitchellii mitchellii）为联邦濒危物种，目前仅在美国东部18处高度隔离的栖息地有分布。当前普查采用沿栖息地漫游行进的方式，记录观测到的蝴蝶数量。该普查在人力与时间投入上效率较高，但所得数据无法用于估算种群丰度。标记释放重捕调查可获取种群统计参数的估算值，尽管该方法的实施频次较低，但需要投入大量人力与数周野外工作，才能得到误差处于合理范围的估算结果。
3. 本研究在美国密歇根州下半岛的一处栖息地，采用基于样线的分层距离采样法（hierarchical distance sampling）估算米切尔眼蝶（N. m. mitchellii）的种群丰度。该方法仅需1名观测者以步行速度沿多条样线行进，记录观测到的蝴蝶数量及其与样线的垂直距离。研究结果表明，该方法的成本效益与漫游式普查相当，同时可生成可靠的蝴蝶种群丰度估算值。