Last weekend found me once again at the Wildwood in Kent, on a small mammal trapping course. I haven’t had chance to do small mammal trapping since university, so it was good to refresh my knowledge and skills. There is something so exciting about finding a trap with the door closed and wondering what is inside!
The first part of the course looked at the UK’s small mammals and the main ways of identifying them; bank vole Myodes glareolus; field vole Microtus agrestis; water vole Arvicola amphibius; wood mouse Apodemus sylvaticus; harvest mouse Micromys minutus; house mouse Mus musculus; yellow-necked mouse Apodemus flavicollis; dormouse Muscardinus avellanarius; common shrew Sorex araneus; pygmy shrew Sorex minutus; water shrew Neomys fodiens; and the black rat Rattus rattus.
We then looked at the types of traps available for small mammals; by far the most popular (and most expensive), is the Longworth trap (left). Longworth traps are mainly used to capture mice and voles, with extra provisions for shrews – different trapping methods are used for the other small mammal species.
The Longworth trap comprises of a tunnel and a nest box. The tunnel is long enough that when a small mammal gets to the entrance of the nest box, when it steps on the trap mechanism, the tail will not be caught in the door when it closes. The trap mechanisms’ sensitivity can be altered to exclude shrews if you wish. They will be able to wander in and out without the risk of the door closing, as they weigh considerably less than mice or voles.
Now, why would a small mammal want to go inside such a thing? Food of course! The nest boxes are baited with tasty food including sliced apple, wild bird seed mixes, muesli, dried fruit, and even hobnobs and peanut butter! The bait is put into the nest box area first, then a good handful of fresh hay is put in for somewhere for the inhabitant to curl up safe and warm.
The trap door is then set, and the whole thing is placed in suitable habitat – long grass, at the base of a hedgerow, a dry stone wall… The nest box is at an angle to the tunnel entrance to allow any liquid, such as condensation or pee, to trickle out, but it must have enough support to not move or roll over. It is then recommended you cover the trap with vegetation or additional hay. Not only will this help camouflage the trap from public view, but it also helps to insulate the trap; because it is made of metal, large temperature fluctuations are to be avoided.
Nest boxes must be checked at least every 12 hours. The food inside will provide enough moisture for the animal, but much longer than this and they may suffer from dehydration. If you are trapping for shrews, casters (larvae that have pupated) will also need to be added as bait, as they are insectivores. Shrews are much more vulnerable to trapping than mice and voles, so if you do find one, handle it as little as possible – the stress of handling may kill it. Shrews also have added protection under the Wildlife and Countryside Act 1981, so a Natural England general licence is required to trap them.
After the theory session, we all put on our hats, gloves and thick socks and headed out into the snow to check the traps that our tutor had laid the night before. She had put them in a variety of habitats, and covered them in straw to help insulate them.
Only 5 traps had doors closed. For each one, the trap was carefully lifted up and placed inside a large, clear plastic bag. The tunnel was removed and then the nest box gently tiped upside down to encourage the animal to come out. Our first trap yielded a bank vole. And no ordinary bank vole – it was black! This is very unusual for a vole, and we think it may be one of the first recorded in Kent.
After getting an animal out of the big bag, it was sexed and then placed into a smaller plastic bag to weigh. We all managed to have a go at catching and handling the various mammals we caught, and, luckily, no one was bitten.
In the afternoon we went to see some mammals that are part of the Wildwoods captive breeding programme; dormice, water vole and harvest mouse. Though Longworth traps aren’t used for these species, it was really good to see them for future reference. Harvest mice in particular are so teeny and cute!