The bank vole (Myodes glareolus)

 ... and how to humanely trap, and release, small mammals for fieldwork

The bank vole is a small chestnut-brown coloured rodent, with a tail around half the length of its body and a cream-grey underbelly. They have small eyes, a rounded snout, and a full body, with prominent ears that are less visible due to fur coverage. Tail length will be a good indicator of if you have a vole or a mouse, as mice tails are longer; usually the length of the mouse body. 

The bank vole is the smallest species of vole in Britain and is found in woodlands, hedgerows, or grassland areas. Their diet consists of vegetation, fruits, nuts, fungi, roots, and occasionally small insects. The bank vole is native to Great Britain, but can also be found in other parts of Europe, Iberia, Italy, and Western Siberia. Bank voles have a stable population, but with an increase in fragmentation of woodland areas, destruction to hedgerows and such, they will surely be affected. Maintenance of natural areas is important to our abundance and stability of biodiversity. Voles are also important prey for small avian predators, predatory mammalians, and snakes.

                                    

                                                                        (Yrammy, 2020).

 

Trapping small mammals, in the best way possible, for ecological surveying!

The favourite ecological surveying small mammal trap has been the 'Longworth Small Mammal Trap' for many years. The design allows for as little discomfort as possible, with a warm and safe place to be until their release.

The trap consists of two parts, the first part is an entry tunnel that harbours a door-tripping mechanism in order to close the tunnel door. This then leads to a spacious house/nesting box, and they both connect with a metal clasp. The box is spacious and allows plenty of room for nesting materials and food. The door-tripping leaver is adjustable in terms of sensitivity, and the trap will have to be set in order for the function to work.

To begin, have bedding material (such as hay) to fill a section of the nesting box for warmth; hay is a good option for voles too as they are mainly herbivores and will eat some of the hay. For food some good recommendations are:

• Carrots - food, and will also provide hydration.
• Seeds - ideal for granivores such as mice .
• Casters - fly pupae which will accommodate for insectivores such as shrews.
• Apple - food, and will also provide hydration.
• Peanut butter - an attractant for all species.

Example of how the nest box should look (like a 5 star hotel!)

The minimum number of samples when looking at population data is 30, and during this independent study we used 60 traps. This was repeated twice, once during day time and once over night.

Depending on where the traps are placed, you will be more likely to be in the territory of a certain rodent; for example woodland area will be likely for wood mice, and hedgerow/open area will be ideal for voles. In the conservation area at UEA, there is a good mix of area types so traps were set out in different areas and numbered wooden steaks were used to track where they were placed on collection. Making a note of the numbered steaks according to the area placed will allow for releasing in the same area. Setting the traps overnight gives a much higher chance of collecting the small mammals, as they are most active during the evening/early morning.

When collection begins, a clear idea of which trap has been successful will be evident by a closed door. Traps can be collected and placed in order alongside their numbered steaks; having a system such as closed door traps facing one direction, and open door traps facing another might be useful. 

When opening the traps, opening them into a clear sample bag gives the opportunity to inspect the small mammal and identify successfully. The latch will need to be unhinged and then the tube can be removed in order for emptying the contents carefully into the bag for inspection. Checking the tube for any detritus will also give you a good idea of what to expect in terms of inhabitants. 

Ensure to carefully release the small mammals where they were found, according to the numbered steaks used.

Identifying the rodents

When there is a small mammal in the bag successfully, carefully moving the mammal into the corner of the clear bag and removing any material from the nesting box will aid in identification. Gently turning the rodent on their back and having a quick look at genitalia will give a clear idea on sex; looking for mammary glands for females and testes for males. 

Size of mammal is a good indicator of age, juvenile rodents feet will generally look large for their bodies. 

References:

Yrammy. (2020). Bank Vole. [online] Available at: https://www.ispotnature.org/communities/uk-and-ireland/view/observation/796430/bank-vole [Accessed 29 Mar. 2023].