Nest by nest: Protecting Britain’s smallest mammal Written by Antonia Illingworth. Posted 30th April 2025 Meet the Harvest Mouse The harvest mouse (Micromys minutus), first scientifically described by Gilbert White in the 1700s, but appearing in Welsh folklore before the 14th Century, is one of Britain’s most charming small mammals. With characteristic gingery yellow fur, a white belly, and a highly mobile tail to cling onto grass stems, the harvest mouse is a minute creature, weighing less than 10 grams. Harvest mice live for around a year and half on a diverse diet of fruit, seeds and invertebrates. To build their nests, harvest mice favour reeds and tall grasses, that are often found at field margins or on road verges. The mice cleverly weave their spherical nests by balancing with their tail and specially adapted toes. Changes to weather patterns, farming techniques, and a decrease in habitat availability have led to harvest mouse decline. Now harvest mice are on the Red List for Britain’s Mammals, alongside red squirrels and hedgehogs. Image right: I found this nest next to a watery ditch woven into tall grass. A collection of nests were found in this area. We took a note of their GPS locations. . Citizen science in action In an effort to conserve the species, the National Harvest Mouse Survey was launched in 2021, with yearly surveys running from October to March. In the 2023/24 survey year, 1,618 nests were recorded in Britain. While important in their own right, harvest mice numbers also indicate the quality of a habitat and its ability to support predators like owls, hawks and polecats. This year, I got to be involved with a nest survey at Queens Wood – one of our younger Community Woodlands, planted with 48,625 trees and shrubs between 2021 – 2023. . Nest hunting at Queens Wood Recognising harvest mouse nests is easy once you know what to look for. There are a few characteristic features: a woven ball of grasses about the size of a tennis ball, with a small exit hole. The nests to take note of have all been abandoned, so you’re unlikely to disturb any timorous beasties. However, if you find a nest made up of still-green materials, or without any visible exit hole, it’s best to leave it alone – it could still be occupied. Harvest mice have up to 3 litters of pups annually, with the breeding season running from late spring to autumn. Each nest takes a mouse a single night to build - an impressive feat of engineering. At Queens Wood, I searched for nests with Senior Ranger, Nicola Ceconi, and a team of volunteers led by Ken Winder. We spread out to search, parting tussocks of long grass and taking a GPS reading whenever a nest was found. It was a lovely day out – exploring one of our newest woodlands, and uncovering a secret city of tiny homes. Interestingly, multiple nests tended to be found in close proximity to each other, potentially due to clumps of particularly favourable habitat. Connectivity between suitable habitats is a key part of helping nature thrive, and is one of the many factors taken into account when planning our woodland planting. . A typical nest - a tightly woven ball of grasses, often hidden in tall vegetation A harvest mouse at home in its nest Volunteers surveying for nests in the Forest . Helping harvest mice thrive Harvest mice aren’t alone in their need to be conserved – a quarter of native British mammals are at risk of extinction. Citizen science has an important part to play in understanding mammal presence and distribution. You can help by downloading the Mammal Mapper App and monitoring the mammals in your local area, or by joining your Local Mammal Group. Survey techniques and other evidence of harvest mouse presence, such as skulls found in owl pellets, can also be used to reveal the success of reintroduction projects, such as that at Chester Zoo’s Nature Reserve, which took place in the early 2000s. More recently, landowners in the North York Moors National Park released 300 harvest mice with funding from Defra, after noticing the presence of cocksfoot grass – a species that harvest mice favour as a nest building material. . What you can do Harvest mice have also been found in cultivated gardens like RHS Hyde Hall in Essex. While it might be tempting to keep everything in your garden looking neat and pristine, nature generally prefers a wilder approach. Gardeners near fields or farmland might be able to encourage harvest mice by leaving grassy areas to grow long and avoiding the use of pesticides. For more inspiration and ideas about how to help nature thrive in your garden, have a look at these tips provided by The Wildlife Trusts. By leaving uncut grassy areas – some until the end of September, and others all year round, the Forest of Marston Vale Trust provides plenty of harvest mouse friendly habitat. As a result of this management strategy, we’re very glad to have evidence of harvest mice making their homes on 8 of our 13 sites. . If you’re passionate about protecting the species around you, why not sponsor a habitat in the Forest? Manage Cookie Preferences