Imperfect detection of individuals in threatened wild populations is common and can obscure real population trends when it is unaccounted for in population monitoring, and therefore impede conservation decision making. For many threatened insects, there is a lack of biological information or available long-term data to inform how best to practice data collection and population monitoring. Here, we inform the design of a long-term population density monitoring protocol for Brachaspis robustus, a Nationally Endangered grasshopper endemic to the Mackenzie Basin of New Zealand. We use removal sampling (repeated visual searches of a predefined area where any individuals found are temporarily removed to achieve successive depletion) during a single austral summer season (November to March) to rapidly quantify seasonal and demographic visual detectability. Juvenile instars dominated population composition in all months except December and males represented > 50% of monthly captures. Adult females were 2–3 times larger than adult males, and 79% of those captured were found during the first search of an area compared to only 52% of adult males. The odds of detecting an individual increased by 6% per 1 mm of body length. Removal sampling was found to be an effective method for rapidly informing future long-term monitoring design for a visually cryptic, threatened insect. Recommendations include monitoring adult females as an index of population size, restricting monitoring to when adult abundance peaks (November and December), and conducting multiple monitoring events within peak months to counter the effects of daily and seasonal variation and imperfect detection.

中文翻译：

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为国家濒危蚱蜢的长期种群密度监测协议的设计提供信息：清除抽样作为估计个体检测概率的基础

在受威胁的野生种群中对个体的不完美检测很常见，如果在种群监测中没有考虑到，可能会掩盖真实的种群趋势，从而阻碍保护决策的制定。对于许多受威胁的昆虫，缺乏生物学信息或可用的长期数据来告知如何最好地进行数据收集和种群监测。在这里，我们为 Brachaspis robustus 的长期种群密度监测协议的设计提供了信息，这是一种新西兰麦肯齐盆地特有的国家濒危蚱蜢。我们在单一的南方夏季（11 月至 3 月）期间使用移除抽样（对预定义区域进行重复视觉搜索，在该区域中发现的任何个体都被暂时移除以实现连续消耗）来快速量化季节性和人口统计学的视觉可检测性。除 12 月外，所有月份的幼虫都占种群构成的主导地位，雄性占每月捕获量的 50% 以上。成年雌性比成年雄性大 2-3 倍，在第一次搜索区域时发现了 79% 的被捕获者，而成年雄性只有 52%。检测到个体的几率每增加 1 毫米体长就增加 6%。发现去除采样是一种有效的方法，可以为视觉上神秘的受威胁昆虫快速通知未来的长期监测设计。