Supporting the harvest mouse at Carymoor

Supporting the harvest mouse at Carymoor

The Carymoor team has been working to encourage the harvest mouse on its nature reserve.

Since 1996 Carymoor has transformed 80 acres of capped landfill into a mosaic of different habitats, with meadows, wetlands, and woodland. The area was used as a landfill from 1970 to 2000 and contains over 2 million m3 of waste, mostly coming from households in South Somerset and Mendip. The waste is covered over with 1 to 2m of clay which cap the site, and this was the blank canvas Carymoor took on when they started their habitat creation work. Since work began in 1996 the reserve has become home to a number of priority species including the Small Blue and Brown Hairstreak butterflies, Great Crested Newt, Slow Worm, Grass Snake and the harvest mouse. Carymoor is supported by a dedicated team of volunteer wildlife recorders who help to monitor the numbers of key species.

The harvest mouse (Micromys minutus) is a generally elusive small mammal and has become scarcer in recent times, largely due to a decline in suitable habitat and changes in agricultural practices. The mouse is mostly nocturnal and is the only British mammal to have a prehensile tail which is uses to move through long grass. The harvest mouse builds a unique spherical nest by weaving together grasses. Although nests had been found at Carymoor over the years, its distribution across the nature reserve was not well understood. Together with Viridor we have developed a site management plan and this identified the harvest mouse as one of our key species. We wanted to undertake some specific monitoring to find out about the population and where possible to encourage the harvest mouse through the provision of suitable foraging and overwintering habitat. 

Thanks to a grant from the Pat Hill-Cottingham fund, Carymoor was able to invest in 12 Longworth mammal traps to carry out a monitoring programme. 2 of the team attended a training course learning how to handle small mammals, what legislation was involved, and setting up the transect at Carymoor. The first transect took place in October 2019 and although no harvest mice were found the team gained valuable practice with the traps and process. In November 2019 a nest ball search was conducted on the transect and 7 nests were found. All the nests were found in rough grass margins on the site edge where the hedge has been recently laid. As a result, we now cut the margins in small sections on rotation to encourage rough grassland and to suppress dominant bramble growth. The cut is undertaken after nest searches have been completed in November / December.

Although the monitoring programme was disrupted by Covid in 2020, further nest searches were carried out in November and December 2020, with Carymoor staff assisted by volunteers. 8 nests were found and for the first time 2 nests were found on the capped area of the nature reserve, meaning the harvest mouse has migrated across the perimeter road on to the main site. We were delighted to find this and have extended their monitoring area for 2021. The team is still yet to catch a Harvest Mouse on the monitoring transect but with more regular monitoring planned for 2021 it can only be a matter of time!

This project underlines the important role brownfield sites can play in protecting wildlife, providing safe havens for nature and transforming the legacy of wastefulness into something more positive.