The Harvest Mouse (Micromys minutus)

The Eurasian Harvest Mouse (Micromys minutus) is the smallest rodent in Britain, weighing 6g as an adult, that is less than a 2 pence coin! On the IUCN red list, it is listed as least concerned however it is recognised as a priority species on the Biodiversity Action Plan (BAP) as they seem to have become scarcer over the years. Along with being Britain’s smallest rodent it is also Britain’s only mammal with a prehensile tail which allows it to grasp vegetation like flower stems and move through the long foliage that they favour. With few records in Cumbria we are asking you to get involved in looking for this remarkable species to better understand their distribution within our county!

Ecology

The harvest mouse does not hibernate over the winter and instead remains active throughout the year. However, the harvest mouse’s behaviour can change depending on the season in which you are looking for it. Throughout most of the year it is mostly nocturnal but during the winter it spends more time out of its nest during the day than it would at other times of the year. These nests can be found in tall tussock grasses, hedgerow, reedbeds, ditches and brambles and can the best indication of a harvest mouse’s presence in the area. During breeding season (May-October) this mouse will make breeding nests around 10cm in size and 30-60 cm off the ground amongst long grass.  The nests that the mouse creates falls to the ground in Autumn.

Over the winter they make smaller nests about 5cm in size and closer to the ground in order to conserve heat. These nests are made from shredded up pieces of grass woven together to create a hollow ball shape and chewed up leaves are used to line the inside. They are woven onto the stem of the grass or reeds. The harvest mouse has a varied diet of seeds, berries and insects but have also been known to eat moss, roots and fungi. During the warmer months, the mouse will gather a stash of food which it will eat over the cooler months when food is scarce.

The distribution map shows where the harvest mouse has been previously recorded in Cumbria.

In the last 20 years CBDC has had 2 records in the North of Cumbria (not seen on the map). There are however these records indicate that the harvest mouse could still be in the county with 5 southern and 2 northern sightings since 2000.

This may not indicate that harvest mice are not present in North Cumbria or more wide spread in Southern Cumbria, as the harvest mouse is skittish and small it is harder to find. This means that recorders need to go out specifically looking for harvest mice, especially their nests in a piece of habitat that would be suitable.

Where are they now?

Help CBDC and the Cumbria Mammal Group get a better understanding of the harvest mouse in Cumbria.  All we need you to do is go out and look for their nests during from December 2020 – February 2021.

How to find harvest mouse nests

The best indicator is to look for their nests. These can be found higher up woven into the stems of long tussock grass or reeds if it is a breeding nest (May-October). Breeding nests can be tennis ball sized made up of long woven pieces of grass. Nonbreeding nests can be found throughout the year. They are in the same habitats but lower down in the base of the tussock grasses or reeds. These nests are smaller and have a more elongated appearance.

When looking for harvest mice nests look for any places with long tussock grasses or reed beds where there is minimal disturbance from humans, livestock or dogs. Wearing gloves, carefully part the long grass or reeds looking for the nests near the base of the stems or if it is during the breeding season higher up off the ground. If you find a nest do not disturb it as the animal could still be inside. Instead lay a small ruler or standard pencil/pen near the nest and take a photo. Then cover the nest back up as you found it.

How to identify the harvest mouse

Harvest mice are very small (50-70-mm) and a golden-brown colour with a white underside. They also have a blunt nose which can give them an appearance that looks similar to a vole. With a prehensile tail that wraps around the steam they are on. While the harvest mouse is easily identified it is rare to see one. This could be contributed to their excellent hearing that can pick up sound from 7m away giving them time to hide.

View film: Harvest Mouse Identification and Recording

To make a record valuable to us we need to know five main points:

• WHO spotted it?
• WHAT was it?
• WHERE was it? – (a grid reference and location name is preferred)
• WHEN was it spotted?
• HOW many were there?

If you took a photo of the nest please include this in your record. This will enable us to better verify the find.

Records can be submitted on the CBDC website, IRecord or emailed to Stuart Colgate (recordingofficer@cbdc.org.uk)

All small mammal records submitted using this page will be sent immediately to John Martin for verificatio. John is our Cumbria referee for mammals and will be happy to look at any evidence of harvest mouse. He will also verify any mammal records submitted on iRecord.