Small Mammal Trapping on UEA Grounds

On Monday 6th March 2023, I went to the conservation area on UEA grounds to do small mammal trapping for the first time. I did this for practise, and to see which small mammal species were present and to gain an idea on their abundances.

Setting up the traps:

To trap the small mammals, we (my group) used these Longworth small mammal traps, which consists of a metal box or ‘house’ with a separate tunnel, which attaches on. The house contained the food and treats used to lure in the small mammal, whilst the tunnel has a tripwire-like mechanism, which triggered when something crossed it. When triggered, a flap would conceal the entrance, trapping the mammal inside the box.

The Longworth traps we used

Due to the large variety of small mammals (mice, shrews, and voles) present on UEA grounds, we had to ensure that all species were catered for food-wise. For this, we used hay, carrot, blowfly pupae (casters), apple, seeds (sunflower hearts), and (the all-important) peanut butter. Voles are herbivores, so the hay and carrot were primarily for them. Shrews are insectivores, so hence the casters. Mice are granivores and had seeds. Carrot and apple were used as a water source, and hay also for warmth. The peanut butter is a universal attractor for the small mammals, but cheap custard cream biscuits could have been used as a substitute too.

We placed the traps along a transect against the woodland fringe within the conservation zone, in pairs, about 2 m away from each pair (so 30 sites of 60 traps). This is because the mice prefer the woodland area, so they can climb and reach berries and other foods easily, and the voles like the grassy, meadow areas due to its openness. The shrews, on the other hand, aren’t that fussy about the habitats can be found in both grassland and woodland.

Trap collection and findings:

In terms of specific small mammals, we were aiming to find yellow-necked mice (Apodemus flavicollis), wood mice (Apodemus sylvaticus), bank voles (Myodes glareolus), common shrews (Sorex araneus), and pygmy shrews (Sorex minutus). However, out of all these species we only caught yellow-necked mice, wood mice, and bank voles.

After collecting the traps again (after a period), we counted how many out of the 60 traps set out were triggered (results below). We then took the triggered traps, unlatched the tunnel, and carefully emptied the contents into plastic bags. This was so we could observe the small mammals without them escaping easily. We made sure the other contents (hay, etc.) were taken out for clearer observations, and that the bags partially open to allow air flow so the small mammals didn’t suffocate.

(A very wet) Bank vole
Wood mouse (apologies that the pictures aren’t the clearest)


As previously stated, we did not catch any kind of shrews, and this may be because they are rarer than the other small mammals, or they do require a different location to place the traps, or some other environmental factor could have affected this (hibernation for example).

On the other hand, we did catch varying numbers of each of the other predicted species (shown in table below).

From this table and graph, yellow-necked mice are represented to be rarer than the wood mouse and bank vole. The reasons for this could be like the ones I suggested for the lack of shrew recordings.

We did set these traps up again in the evening to record the findings the following morning, and these were the results gained:

We overall caught more small mammals this time round than the previous day! This could have been due to the small mammals becoming trap-friendly after time (especially if there’s peanut butter involved).

Unfortunately, there were no yellow-necked mice present in the traps. This may have been because the mice became trap-shy and ran away when they detected the trap.

Also, there were 13 false traps this time, where the trigger was set off, but not small mammals were inside. This may have been due to something else triggering the trap, like insects or rainwater (for example), especially if the sensitivity is high. The traps may have also not been set properly, leading to the doors closing if anything happens or over time.


To improve this study, I would leave the traps by where I see signs of small mammals. This could be in the forms of holes, or runs present, as well as droppings. This could however, lead to the investigation becoming bias, and the production of skewed results. I understand the best method is to use a more random or systematic method of selecting where to place the traps, but in this scenario where I want to know which species are present, and their abundances, then the new suggested method may be more in favour just this once.

The method of placing the traps out for several days (with checking them each morning/evening) has proven to work in this investigation. So, by placing the traps out for more days could increase the chances of trap triggers. This would work in favour for the trap-friendly small mammals but wouldn’t for trap-shy ones. The other problem with this is also how time consuming setting up and checking/clearing each trap would be.