Devon Harvest Mouse Project

The traditional image of harvest mice is of a cute little mouse at the top of a stem of oats or similar arable crop, or maybe posing inside a juicy apple. However over the last few years there have been very few harvest mice recorded, and data from across the country suggested a serious decline in numbers. With this in mind, Devon Mammal Group has set up the ‘harvest mouse project’ to find out where in the county harvest mice can still be found.

Harvest mice (micromys minutus) are both very small and elusive, so rather than looking for the mice, we search for their nests instead. These nests are amazing spherical structures, often at the top of clumps of grass, made of woven grass and firmly attached to the vertical stems. The nests start off as green, but fade to brown as they age, so are easier to see in the autumn. They also start off as very small and tight, but expand as the babies grow, meaning that they can only be used once. Harvest mice breed from approximately March until early October, so the project starts in October and runs until March, training people to look for nests and coordinating a county-wide survey.

Read the 2017-2018 report here: DMG Harvest Mouse Project Report 2017-2018.

Project Map

Devon has been divided into roughly 90 hectads based on the Ordnance Survey map, and checks are carried out by volunteers. Harvest mice like nesting in long grasses (such as cocks-foot and purple moor grass) and looking for nests is not complicated, more like looking for a tennis ball in a clump of grass. Once a nest is found, it is then checked by the volunteer to see if it is made up of short little pieces of grass (vole nests) or long woven pieces (harvest mice nests) and a photo taken. If it is a harvest mouse nest, then people can fill in a 3 minute long survey form on . This gives us invaluable information about where the nest was, what it looked like, the type of habitat it was in and how big it was. The information is uploaded to our project map, and also shared with Devon Biological Records Office.

Anyone can take part, and although we offer training sessions to help people know where to look, training really isn’t necessary: just look out for clumps of long grass and you never know what you might find! If you would like to be added to our mailing list to hear more about the project and training/group surveys, please email

Why winter?

Surveying a small mammal over the coldest months of the year may seem a little unusual. We are not looking for the mice themselves (although we will be doing some trapping too). Most of our surveys are going to be nest searches. Harvest mice build beautiful spherical nests during the summer month to live in. These are set above the ground and made from grass, stripped and entwined around itself. During the summer these nests are almost impossible to find. But when the vegetation starts to die back, and the grass dries they become easier to spot. It’s still tricky, though, but training helps.

So what is the aim of the Project?

We would like to survey as many tetrads (10 x 10 km grid squares) as possible in Devon. Devon is a large county, and with over 90 tetrads this is no small challenge. However, we will be training up anyone who wants to learn, in the hope that the new found knowledge will be put to use and more records will come flooding in! We will be running a number of dedicated training days, as well as smaller training sessions across the county over the next few months. There will be one in your area, so keep an eye on the website to find out when there is one near you!

You can find the map and information on records HERE. Submit a record using our online form HERE.