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

Abstract

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.

Top‐down limitation of lemmings revealed by experimental reduction of predators

“…Camera traps have recently been proposed as a promising method to monitor lemming activity in winter (Soininen et al. ) and such methodological innovations will be necessary to fully understand lemming cycles.…”

“…, Soininen et al. , b). Nest density was calculated as the total number of nests occupied by brown lemmings divided by the size of the searched grid.…”

Spatial distribution in Norwegian lemming Lemmus lemmus in relation to the phase of the cycle

“…The spring migration is normally triggered by the snowmelt, and lemmings have been observed to move from winter habitat at higher altitudes to summer habitats up to 3 km away and 200 m lower to avoid snow bed habitat that is drying up during summer (Henttonen and Kaikusalo 1993), and hence, summer distribution does not have to be closely linked to winter distribution. However, as that the summer distribution of lemmings during the increase phase was linked to landscape features that likely offer good overwintering conditions, studies of winter distribution would be interesting (although technically difficult to carry out, but see Soininen et al 2015), to investigate if lemmings apply a year around strategy to limit seasonal migration when possible. Such a strategy could have several benefits as limited seasonal movements could reduce the risk of predation (Lagos et al 1995) and the risk of ending up in a habitat of poor quality (Lin and Batzli 2001).…”

Biodiversity estimates from different camera trap surveys: a case study from Osogovo Mt., Bulgaria

“…However, this is not possible for micro mammalian species, where it is often difficult to identify the animal even to the genus level. This is one of the disadvantages of the conventional camera trap studies, although some efforts are made recently to propose a new camera trap study design for small mammals (Glen et al, 2013;Mccleery et al, 2014;Soininen et al, 2015).…”