By Rose Toney and Nick Littlewood
Camera traps have revolutionised mammal recording. With lowering costs and increasing functionality, many Mammal Society members now use them for monitoring local wildlife. They are a window into a secret world, helping to monitor movements of Badgers, Foxes, deer and other species, by day and night. Camera traps are generally optimised for detecting and recording these larger and medium-sized species. However, with some low cost adaptation, camera traps can also be used for monitoring our smaller species, including mice, voles and shrews, as newly described in an open access paper in the European Journal of Wildlife Research.
Small mammal monitoring typically involves live-trapping. This is demanding in terms of time input (traps need checking every few hours), requires skilled staff or volunteers for handling mammals and also comes with a welfare cost, including risk of mortality, to the animals that are caught. Camera trapping small mammals can overcome these issues – cameras can be left unattended for any duration, no mammal handling is needed and welfare risks are minimal. What’s more, multiple species can be recorded at a single survey station.
The key to recording small mammals is to bring the subject right up to the camera. This can be achieved by strapping the camera trap to the end of a baited, open-ended box – see images above. A close-focus lens (similar to those used in reading glasses) enables the camera to focus on the subject, whilst covering the flash unit prevents the over-illumination, or “white-out”, that is familiar to camera trappers. The method is described in full in the paper.
Following some early-days trial and error to optimise the technique, we have now used this method for many years for monitoring and recording small mammals. One success was generating multiple species records for the Mammal Atlas of North East Scotland and the Cairngorms, including records of Wood Mice in every one of the 25 tetrads in a 10-km square. We have also targeted Water Shrews and, thanks to input from two fantastic university dissertation students, have substantially increased the number of recorded sites in the region. In addition, the boxes attract occasional visits from other species and seem to be especially good at generating records of Weasels, perhaps attracted by the smell of their potential prey. A compilation of video clips from the box features on the Mammal Society’s YouTube channel.
One project, featured in the paper, entailed using the technique to reveal how small mammal populations respond to blanket bog restoration in northern Scotland. Extensive areas of blanket bog naturally have few small mammals and also few predatory mammals, such as Foxes or Pine Martens. Camera traps showed that areas planted up with conifers had more Bank Voles and Wood Mice. These populations can bolster numbers of the predators, to the detriment of nearby ground nesting birds. The camera traps recorded fewer small mammals following restoration management (tree removal and drain blocking), but still more than in undamaged bog, meaning that restoration areas may still sustain predators, in the short to medium term at least.
A real bonus for us has been learning more about small mammal ecology and habitat use. We’ve noticed that Wood Mice are happy to feed together, with up to six squeezing into the box at one time. Voles generally follow a one-in-one-out policy and shrews are the least sociable of all. We’ve been delighted to find Water Voles high up in Scottish glens and Water Shrews alongside a wide range of waterbodies but also a long way from water.
It is no exaggeration to say that whilst camera trapping has revolutionised our mammal recording, the technique described in the paper has revolutionised our camera trapping. It won’t replace live-trapping in all situations, but it opens up the possibility for far more people to record and discover the species that comprise this often overlooked part of our mammal fauna.
Littlewood, N.A., Hancock, M.H., Newey, S., Shackelford, G. and Toney, T. (2021) Use of a novel camera trapping approach to measure small mammal responses to peatland restoration. European Journal of Wildlife Research, 67:12.