Blog: A big focus on one of Britain’s smallest mammals

Jamie Baker, Animal Manager at Battersea Park Children’s Zoo, introduces the BIAZA Focus Group for a little species with a large purpose...

“Mice to meet you!” From BIAZA’s brand new Harvest Mouse Focus Group (HMFG). We are delighted to have established this group to support zoos caring for harvest mice whilst also developing a management plan for harvest mice kept in BIAZA collections. Our objectives have been to survey the current captive population of Eurasian harvest mice (Micromys minutus), develop a husbandry care-sheet, reintroduction guidelines and explore potential research projects to better understand the species.

Last month, the release of the State of Nature report highlighted a significant decline in U.K. biodiversity. Nearly 1,500 UK species are at risk of extinction, following a 19% decline in species diversity since 1970. These shocking statistics are reflected in the wild population of Britain’s smallest mammal, with Eurasian harvest mice classified by the IUCN as Near Threatened in Great Britain.

This decline is certainly a driving force for zoos moving towards a stronger focus on our own native species. However, just as we follow scientific guidance on the population management of our more exotic zoo residents, this same monitoring should be implemented for our native species to ensure long-term population health, increasing the chances of success within our conservation efforts.

To establish an effective management strategy for harvest mice within BIAZA zoos we are pleased to introduce Catherine Doherty from Woburn Safari Park as the BIAZA Species Monitor for Eurasian harvest mice. Catherine, alongside the HMFG is excited to share a brand-new care-sheet for the species, as well as our initial population survey findings that will inform our next aims and objectives.

Our initial survey shows 517 harvest mice across 13 BIAZA zoos. Current populations are held in a variety of large mixed sex exhibits, breeding pairs and single sex groups. Catherine is now using this data to set up our first official ‘BIAZA Monitor’ – a project to monitor changes in numbers and holdings and to inform decision-making on breeding strategies and transfers between zoos, ensuring we breed and maintain the healthiest possible harvest mice!

Many zoos and aquariums are expanding their work in native species reintroduction projects, with some collections currently partaking in successful harvest mouse survey and release projects, such as that by Battersea Park Children’s Zoo and New Forest Wildlife Park in partnership with Ealing Wildlife Group and Ealing Council. However, the current status of wild harvest mice in the UK is not accurately known. A national survey by the UK Mammal Society is underway, so our HMFG recommend that zoos considering new release projects pause until those survey results are in, and instead of releasing animals, work to survey their own potential release sites for three years to ensure there are no harvest mice already living on those sites.  This is important as recent research suggests that harvest mice releases have a low success rate when mice already inhabit the area. To further ensure that all future releases are as successful as possible, we are hoping to coordinate some research, including genetics research looking at provenance and relatedness of the captive zoo population, and separately looking into the health of wild populations.

BIAZA members who would like more information on the work of the HMFG, can get in touch with Catherine Doherty via email at [email protected] . Be sure to listen out for most HMFG plans and projects getting underway in 2024!

All blogs reflect the views of their author and are not necessarily a reflection of BIAZA's positions.