Under the snow: a new camera trap opens the white box of subnivean ecology

Snow covers the ground over large parts of the world for a substantial portion of the year. Yet very few methods are available to quantify biotic variables below the snow, with most studies of subnivean ecological processes relying on comparisons of data before and after the snow cover season. We developed a camera trap prototype to quantify subnivean small mammal activity. The trap consists of a camera that is attached facing downward from the ceiling of a box, which is designed to function as a snow-free tunnel. We tested it by placing nine traps with passive infrared sensors in a subarctic habitat where snow cover lasted for about 6 months. The traps were functional for the whole winter, permitting continuous data collection of site-specific presence and temporal activity patterns of all three small mammal species present (the insectivorous common shrew, Sorex araneus, the herbivorous tundra vole, Microtus oeconomus, and the carnivorous stoat, Mustela erminea) as well as abiotic conditions (presence/absence of snow cover and subnivean temperature). Based on their successful functioning (only 6% of the photographs appeared empty or were of poor quality, whereas ca 80% were of small mammals and the remaining of birds and invertebrates), we discuss how the new camera trap can enable subnivean studies of small mammal communities. This greatly increases the temporal resolution and extent of data collection and thereby provides unpreceded opportunities to understand population and food web dynamics in ecosystems with snow cover.

全球多数区域的地表在一年中的相当长时段内均被积雪覆盖。然而当前可用于量化积雪下生物变量的方法寥寥无几，绝大多数雪下（subnivean）生态过程相关研究都依赖于积雪季前后的数据对比。为此我们研发了一款相机陷阱（camera trap）原型设备，用于量化雪下小型哺乳动物的活动情况。该设备由安装于箱体顶部且朝下取景的相机构成，箱体被设计为无雪隧道结构。我们将9台搭载被动红外传感器的陷阱放置在积雪期约6个月的亚北极生境中进行测试。该陷阱可在整个冬季稳定运行，能够持续采集目标生境中3种小型哺乳动物的位点出现情况与时间活动模式数据，涵盖食虫性普通鼩鼱（*Sorex araneus*）、植食性苔原田鼠（*Microtus oeconomus*）与食肉性白鼬（*Mustela erminea*），同时还可采集非生物环境数据，包括积雪覆盖状态与雪下温度。基于设备的优异运行表现（仅6%的照片为空或画质不佳，约80%的照片拍摄到小型哺乳动物，剩余照片则记录了鸟类与无脊椎动物），我们探讨了这款新型相机陷阱如何助力小型哺乳动物群落的雪下研究。这极大提升了数据采集的时间分辨率与覆盖范围，从而为理解积雪覆盖生态系统中的种群与食物网动态提供了前所未有的研究契机。