Last week I joined Surrey Wildlife Trust on a harvest mouse survey in wetland habitat beside the River Wey.
Harvest mice are tiny rodents 5cm in length. Their remarkable prehensile tails add an extra 6cm. They live in long tussocky grassland, reedbeds, hedgerows and around woodland edges, building a spherical nest of tightly woven grass, high up amongst the stems. We found several examples at this site:
Nests are the most obvious sign of harvest mouse activity since the animals are especially active around dawn and dusk and rarely spotted in the thick vegetation.
Dozens of rodent-friendly traps of different designs were set in the thick wetland reeds and grasses. Surrey Wildlife Trust staff and volunteers returned three times each day over the course of a week – at dawn, midday and dusk – to ensure that no trapped animals were left for any longer than necessary.
After retrieval from the trap harvest mice are transferred to a transparent bag for weighing and sexing:
Once the details of each rodent have been recorded a small patch of fur is trimmed to identify any animals which are subsequently re-captured.
The highest number of individuals captured was 12 one morning, making this the most abundant site for harvest mice in the county at present.
With thanks to Surrey Wildlife Trust staff and volunteers.