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September’s species of the month: Harvest Mouse, Micromys minutus

Harvest Mouse Matt Binstead

Harvest Mouse
Photo:Matt Binstead

Harvest Mouse nest

Harvest Mouse nest

The Mammal Society’s
National Harvest Mouse Survey

What is the Harvest Mouse?

The Harvest Mouse (Micromys minutus) is Britain’s smallest rodent and is an iconic character in the countryside. Once they become an adult, harvest mice could live for 12 to 18 months, but many only survive a single winter through to the following breeding season. They weigh only 5-8g and can be very difficult to spot. Fortunately for wildlife enthusiasts and conservation organisations, they build characteristic above-ground nests which are used for shelter and breeding. The number of nests in an area could indicate the size of the local population although further studies are needed on this.

Why are we planning a National Survey Project?

Harvest mice occupy a wide range of habitats, mainly as the name suggests related to cereal crops. They can also be found in undisturbed grassland such as road verges, hedgerows, field margins and ditches. Favoured foraging and nesting in the summer takes place in tall grass or reed vegetation, moving to ground level as the winter approaches. The UK has undergone increasing industrialisation of farming, with harvests tending to occur more frequently throughout the year, different crop types being grown and the removal of boundary features. These changes to the habitat and habitat fragmentation have been associated with a decline in numbers, although good data on this is not yet available. However, numbers appear to fluctuate greatly both during a year and from year to year. Currently they are placed on the Red List of British Mammals as Near Threatened in Wales, Critically Endangered in Scotland, and Least Concern in England.

What are we planning to do?

Mammal Mapper App

Here at The Mammal Society, we consider the lack of information of this species as unacceptable, so we are taking matters into our own hands and calling on volunteers to help us. This Autumn (2021) will be the beginning of our National Harvest Mouse Survey! We will be asking volunteers, with guidance, to identify suitable survey sites (roughly 200m2 in area) and to spend time looking for nests in that site area. It is up to the volunteer how long they search for, but it is essential we receive information on the site location, survey date, duration of search, number of surveyors, predominant habitat of the site and the number of nests recorded. Additional data such as the name of the site and evidence of site management would also be useful for us to receive. Photographs of the site and nests would be particularly welcome. Previous studies did not take into account the effort volunteers put into surveying, nor did they account for the absence of nests. Therefore, it is very helpful to hear from you if you did not find any nests - the absence of nests is just as important data to us as the presence of a nest. To make the survey easier for volunteers and for our analysis, we recommend volunteers use the Mammal Mapper app - this records much of the information we need automatically and connects directly to our database. However, we recognise that some will want to stick with pencil and paper and therefore, we provide a printable recording sheet to download so you can still participate. ANYONE can take part in this project - we will be providing training material so you are fully prepared to join in with this exciting survey and we are happy to answer any questions that you might have - be it about the training, dates, app or identification.

What is in it for us?

The Mammal Society is a national charity that is dedicated to supporting populations of all mammals - large and small - in Great Britain. We rely on funding, donations and items that our volunteers and customers buy from us so we can perform our work. However, the harvest mouse survey is a wonderful opportunity for us to engage with volunteers from all over the country and we really do need your help to learn more about this iconic British mammal. You will also be contributing toward scientific research that will help inform local councils and national government on how land is managed to conserve this and other species. Who says you need a PhD to contribute to important research?

About and further information

The Mammal Society
If you are interested in becoming involved with the project, please visit The Mammal Society Website where you will find further information on who to contact, how to prepare, and what to do. We hope that you do take part in this national survey - every record or lack of one counts, so please do get involved!

Dan Bowen


Previous species of the month:


Every month it is our aim to highlight a species that is “in-season” and, although not necessarily rare or difficult to identify, has been highlighted by our local recording groups as being somewhat under-recorded and for which new records would therefore be welcomed.

If you or your recording group are aware of species such as this then please contact Bob Foreman.