Diminutive harvest mice found at Cwm Colhuw Nature Reserve, Llantwit Major

Recently volunteers from the Wildlife Trust of South and West Wales (WTSWW) and the South Wales Mammal Group have been surveying some of our reserves on the hunt for the UK’s smallest rodent, the harvest mouse (Micromys minutus) and they have found evidence of them at our Cwm Colhuw Nature Reserve, Llantwit Major.

Harvest Mouse Vaughn Matthews

Harvest Mouse Vaughn Matthews

Harvest mice adults weigh only 6g and measure 5-6cm in length (excluding tail)! They have a distinctive russet appearance and a long tail with a unique prehensile tip to assist them in clambering around in the tall vegetation which they inhabit. Harvest mice, along with many other species have declined in recent years due primarily to habitat loss and fragmentation. They prefer to live in areas of tall, dense, grassy vegetation such as rough grass banks, grassy hedgerows, bramble patches, reedbeds or in cereal crops. A lot of these habitats have been lost with agricultural intensification and general “tidying-up” of the countryside.

There are thought to be about 10,000 harvest mice in Wales, but they are probably under-recorded due to their elusive nature. The most reliable indication of their presence is their circular woven nests that they build in the stalk zone. As they are made with living leaves, they are very difficult to find in the summer but become more visible as vegetation dies back later in the year.

A regular volunteer and South Wales Mammal Group member, Mike Brown, is carrying out surveys looking for these distinctive nests in order to increase our knowledge of the species and their distribution. Cwm Colhuw consists of areas of dense scrub surrounding two fields which have suffered due to lack of management in recent years. The fields were calcareous grassland, which is a relatively rare habitat in Wales, but now lack the diverse flora and less competitive species that characterise this type of grassland. We are currently introducing a program of management to push back the encroaching scrub to increase the area and improve the quality of this grassland for a variety of species including harvest mice.

Harvest Mouse Nest at Cwm Colhuw Vaughn Matthews

Harvest Mouse Nest at Cwm Colhuw Vaughn Matthews

We are now aware of the presence of harvest mice on three of our 90+ nature reserves; Parc Slip near Bridgend, Ffwrd Farm Mire in Carmarthenshire and now Cwm Colhuw. We will be keeping our eye out for signs of this charismatic animal on some our other reserves which have suitable habitat as they are easily overlooked unless looking specifically for them. We will also be running some harvest mouse nest searches at Parc Slip in the next couple of months so please check the Parc Slip events list for details on how you can get involved.