Understanding the factors that limit the abundance of threatened species is critical for the development of effective conservation strategies. However, gaining such knowledge from monitoring programs and using it to inform decision‐making for rare species can be difficult due to methodological issues posed by the problems of distinguishing true absences from false absences and the analysis of datasets dominated by zero counts. The plains‐wanderer (Pedionomus torquatus) is a critically endangered ground‐nesting bird that occurs in grasslands of southeastern Australia. Decline of the plains‐wanderer has been attributed to habitat modification but little emphasis has been placed on the role of introduced predators, such as the red fox (Vulpes vulpes), which have had a devastating effect on small ground‐dwelling vertebrates in dryland regions of Australia. Here, we use a 9‐year time series of spotlight counts to investigate the impact of vegetation structure and fox presence on plains‐wanderer occupancy and abundance. We used distance sampling to determine the effective strip width for sighting plains‐wanderers during spotlight surveys. We then used a hurdle model approach whereby binomial generalized additive models were fitted to presence/absence data within the effective strip‐width across all sites and negative‐binomial models were fitted to an index of abundance at sites where plains‐wanderers were observed. Plains‐wanderer occupancy and abundance fluctuated markedly through time. Where foxes were absent, occupancy (but not abundance) of plains‐wanderers showed a humped relationship with grass height with an optimal height between 50 and 150 mm. Where foxes were present however, this relationship broke down and plains‐wanderers were rarely recorded. Our results suggest that plains‐wanderers should benefit from management strategies that maintain grass height at optimal levels and exclude foxes or effectively suppress their populations. A key message from this study is that if statistical analyses of data generated by monitoring programs for rare species are intended to inform management decisions by identifying relationships between threatened species and drivers of their abundance, there should be consideration of analytic approaches that account for true and false zeroes, high prevalence of zeroes, and the possibility of nonlinear responses.

中文翻译：

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栖息地结构和引入的捕食者限制了濒临灭绝的地面筑巢鸟类的数量


了解限制受威胁物种丰度的因素对于制定有效的保护策略至关重要。然而，由于区分真实缺席和虚假缺席的问题以及对以零计数为主的数据集的分析所带来的方法论问题，从监测计划中获得这些知识并将其用于为稀有物种的决策提供信息可能很困难。平原流浪鸟 （Pedionomus torquatus） 是一种极度濒危的地面筑巢鸟类，生活在澳大利亚东南部的草原上。平原流浪者的减少归因于栖息地的改变，但很少强调引入的捕食者的作用，例如红狐 （Vulpes vulpes），它们对澳大利亚旱地地区的小型地面脊椎动物产生了毁灭性的影响。在这里，我们使用 9 年的聚光灯计数时间序列来研究植被结构和狐狸的存在对平原流浪者占用和丰度的影响。我们使用距离采样来确定在聚光灯调查期间看到平原流浪者的有效条带宽度。然后，我们使用了障碍模型方法，其中二项式广义加性模型拟合到所有站点有效条带宽度内的存在/不存在数据，负二项式模型拟合到观察到平原流浪者的站点的丰度指数。平原流浪者的居住率和丰度随着时间的推移而显着波动。在没有狐狸的地方，平原流浪者的居住率（但不是丰度）与草高呈驼峰关系，最佳高度在 50 到 150 毫米之间。然而，在狐狸存在的地方，这种关系就破裂了，平原流浪者很少被记录下来。 我们的结果表明，平原流浪者应该受益于将草高保持在最佳水平并排除狐狸或有效抑制其种群的管理策略。这项研究的一个关键信息是，如果对稀有物种监测计划生成的数据进行统计分析，旨在通过确定受威胁物种与其丰度的驱动因素之间的关系来为管理决策提供信息，那么应考虑解释真零和假零、零的高普遍率以及非线性响应的可能性的分析方法。