Predictors of Current and Longer-Term Patterns of Abundance of American Pikas (<i>Ochotona princeps</i>) across a Leading-Edge Protected Area

American pikas (Ochotona princeps) have been heralded as indicators of montane-mammal response to contemporary climate change. Pikas no longer occupy the driest and lowest-elevation sites in numerous parts of their geographic range. Conversely, pikas have exhibited higher rates of occupancy and persistence in Rocky Mountain and Sierra Nevada montane ‘mainlands’. Research and monitoring efforts on pikas across the western USA have collectively shown the nuance and complexity with which climate will often act on species in diverse topographic and climatic contexts. However, to date no studies have investigated habitat, distribution, and abundance of pikas across hundreds of sites within a remote wilderness area. Additionally, relatively little is known about whether climate acts most strongly on pikas through direct or indirect (e.g., vegetation-mediated) mechanisms. During 2007–2009, we collectively hiked >16,000 km throughout the 410,077-ha Glacier National Park, Montana, USA, in an effort to identify topographic, microrefugial, and vegetative characteristics predictive of pika abundance. We identified 411 apparently pika-suitable habitat patches with binoculars (in situ), and surveyed 314 of them for pika signs. Ranking of alternative logistic-regression models based on AICc scores revealed that short-term pika abundances were positively associated with intermediate elevations, greater cover of mosses, and taller forbs, and decreased each year, for a total decline of 68% during the three-year study; whereas longer-term abundances were associated only with static variables (longitude, elevation, gradient) and were lower on north-facing slopes. Earlier Julian date and time of day of the survey (i.e., midday vs. not) were associated with lower observed pika abundance. We recommend that wildlife monitoring account for this seasonal and diel variation when surveying pikas. Broad-scale information on status and abundance determinants of montane mammals, especially for remote protected areas, is crucial for land and wildlife-resource managers trying to anticipate mammalian responses to climate change.北美鼠兔（Ochotona princeps）被视为山地哺乳动物响应当代气候变化的指示物种。在其地理分布范围的众多区域中，鼠兔已不再占据最干旱、海拔最低的生境位点。反之，在落基山脉（Rocky Mountain）和内华达山脉（Sierra Nevada）的山地“核心分布区”中，鼠兔的占据率和存续率更高。美国西部全境开展的鼠兔相关研究与监测工作共同表明，在多样的地形与气候背景下，气候变化对物种的作用往往具有细微差别与复杂性。然而迄今为止，尚无研究在一处偏远荒野区域内的数百个位点上，针对鼠兔的生境、分布与种群丰度展开调查。此外，目前人们对气候变化是否通过直接或间接（如植被介导）途径对鼠兔产生最强影响，仍知之甚少。2007年至2009年间，我们在美国蒙大拿州总面积达410077公顷的冰川国家公园（Glacier National Park）内累计徒步超过16000公里，旨在识别可预测鼠兔丰度的地形、微避难所及植被特征。我们通过野外双筒望远镜观测，确定了411处疑似适宜鼠兔栖息的生境斑块，并对其中314处开展了鼠兔活动痕迹调查。基于AICc（修正赤池信息准则）得分对备选逻辑回归模型进行排序后结果显示：鼠兔短期丰度与中等海拔、更高的苔藓盖度以及更高的草本高度呈正相关，且逐年下降，在本三年研究期间累计降幅达68%；而其长期丰度仅与静态变量（经度、海拔、坡度）相关，且在北坡生境中丰度更低。调查的儒略日（Julian date）越早、当日调查时段越早（即正午时段与非正午时段相对），观测到的鼠兔丰度越低。我们建议野生动物监测工作在开展鼠兔调查时，需将这种季节与昼夜节律变化纳入考量。针对山地哺乳动物的种群现状与丰度影响因素的大范围调研信息，尤其是针对偏远保护区的相关数据，对于试图预测哺乳动物气候变化响应的土地与野生动物资源管理者而言至关重要。