A Short Guide to Small Mammal Trapping

based on a guide by Alana Ecology http://www.alanaecology.com

Live trapping small mammals is a useful way of assessing what animals use or occupy a certain area. They can also be used to gauge to size of the population and how they make use of the habitat. The trap most often used in the UK is the Longworth Trap. The only drawback with this excellent trap is its high cost. You can obtain Longworth traps from a variety of companies including Alana Ecology.

Longworth Trap

Alan Ecology also stock the Field Trip Trap. This is a simple trap for occasional use, or where cost is an issue given that the trap costs only 25% that of a Longworth. The trap is manufactured in robust plastic and features a large nest and trapping tunnel. It should be noted that woodmice can chew through an Aluminium Longworth and so plastic traps are likely to be severely damaged unless checked very frequently.

Trip Trap

Where to Place a Trap

Avoid placing traps in areas which are in an open or exposed position. Small mammals tend to avoid open spaces, preferring to go round the edge of a clearing rather than across it. Place traps, for example, against logs on in thick vegetation. Also look for natural pathways through vegetation, chewed food or faeces made by your potential catch.

Try not to disturb too much the area in which you are trapping as the animals may avoid the place. Your traps may be investigated by small mammals but the tend not to like to climb up onto something - ensure the leading edge of the trap is flush with ground level. This will also ensure that the next box is an angle and that urine will drain away. Voles, in particular can produce a great deal of urine and if drainage is inadequate can become soaking wet and the suffer hypothermia.

You need to be able to find your traps again quickly and easily - you do not want to un-necessarily delay the release of a live caught animal. Marking the traps with brightly coloured tape can help but making them too obvious in certain areas in unwise - you do not want other people disturbing or damaging the traps or it's catch.

Spacing the Traps

When surveying an area, two methods are commonly used - spacing traps in a line or in a grid. Traps in a line are useful if you wish to cover a cross section of habitats or you are investigating a hedgerow. Placing traps in a square grid in an area can allow you to see how the mammals use a habitat and gives an indication of population density.

Preparing the Trap

Always provide bedding in the trap - this can be anything warming and non-toxic such as shredded paper, hay or dry leaves. Do not place anything damp in there as this can lead to chilling the animal even on warm evenings. The bedding must be changed after a capture because it will be damp.

Small mammals have high metabolisms and therefore food should always be provided even if the trap is being checked regularly. Death by starvation can be a particular problem with insectivorous mammals.

In cold climates it may be necessary to provide extra insulation around the trap to protect the mammal suffering from hypothermia. With open cage traps, one part should be covered for example with plastic sheeting to protect the animal from strong sun or other adverse weather conditions.


Baiting the Trap

You may need to experiment with different baits but commonly used ones include barley, oats, raisins, seeds, pieces of apple, even peanut butter and chocolate! A piece of apple or carrot will also provide a source of water - this is essential!

Insectivorous mammals such as shrews will need invertebrates for bait and as a source of food. Blow fly pupae (casters) are good and can be obtained from fishing bait suppliers.

Small mammals will be initially attracted to the area of the trap by the smell of the bait. It is advisable not to handle the bait too much especially if you have handled anything particularly pungent before hand e.g. anything perfumed or covered in machine oil.

It is often a good idea to 'pre-bait' the traps several days before setting them. Just leave the traps unset in the area with around and/or in the trap (this is possible with traps such as the Longworth which has a pre-bait catch to allow an animal to enter without triggering). This will allow timid mammals to investigate and get used to the trap being there. This can lead to attracting animals from nearby areas which affect the accuracy of population density estimates or attract species which would not normally occupy that area.


And Remember...

Check your traps regularly - never leave them for more than 12 hours. You may need to check more regularly with shrew trapping as they don't tend to last long in traps. If you can't check your traps often then do not set them.

Some small mammal species are protected by law (shrews in the UK) and you MUST obtain a licence from Scottish Natural Heritage or English Nature if set traps with the intention of trapping any species of shrew. You can avoid trapping shrew by using traps with less sensitive triggering mechanisms or using a trap such as a Longworth with a small 'shrew-hole' drilled through the nest box. This should be fitted with a brass guard otherwise woodmice will enlarge the hole with their teeth and escape!