Released Harvest Mice Thriving 20 years on at Chester Zoo

A reintroduced population of the harvest mouse is thriving 20 years after conservationists from Chester Zoo returned them to the wilds around the zoo. Weighing less than the 2p coin, the UK's smallest rodent is now thriving in the nature corridor around the zoo.

Elsewhere within the United Kingdom the harvest mouse is showing a decline making this latest announcement even more exciting. Scientific studies conducted within the nature corridor and surrounding areas show strong densities of mice breeding nests. These were discovered up to 1.5km away from the initial release site from 2002.

While small the harvest mouse has a mighty impact on the ecosystem primarily as a food source for larger species. Habitat loss and increases in architecture have seen the species enter a decline. This has led to their listing as a ‘priority species’ under the UK Post-2010 Biodiversity Framework and are protected under the Wildlife and Countryside Act 1981.

Chester Zoo began their work to conserve the harvest mouse at the turn of the millennium. Surveys from 1980-2000 showed significant declines in their numbers. Following strict protocols laid out by the IUCN, Chester Zoo returned 960 harvest mice to the conservation corridor from 2002-2004. Their descendants are now continuing to thrive in the wild.

All 960 mice were microchipped by one woman, Chester Zoo’s Registrar, Penny Rudd, who has championed the conservation of harvest mice throughout her 42 years working at the zoo. She explained, ''I’ve been at the zoo for a very long time, and I do see the harvest mouse recovery work I’ve been involved with as a huge legacy. I feel very proud of what we’ve done.''

''When the email dropped onto my desk saying we have strong harvest mouse evidence in the area all this time later — it was just the best feeling in the world!''

Chester Zoo are continuing their work to ensure the future of the harvest mouse through breeding-nest surveys to help provide population estimates and assess the effectiveness of habitat management across the site, in addition to implementing conservation efforts further afield.

Helen Bradshaw, the UK Regional Field Programme Manager at Chester Zoo, said:

"As one of the first breeding and reintroductions programmes that Chester Zoo embarked on 20 years ago, it’s hugely significant to be able to prove that it worked, and we’re delighted that the harvest mice are thriving in our nature reserve and surrounding areas.

Our nature reserve is a flagship landscape for our efforts to recover local biodiversity, and our UK Field Programmes team will continue to manage and improve our habitats in this area for all our native species. Importantly, we’ll also continue to carefully monitor the harvest mouse populations as these data contribute to efforts by the Mammal Society to build up a national picture for this iconic little mouse. With biodiversity in decline across the UK and many species here on the brink of extinction, collecting standardised data is vital to help us create effective strategies that protect and connect habitat.

Chester Zoo say you can do your part to help the harvest mouse by reporting sightings of the harvest mouse to the Mammal Society and wildlife record centres or establishing long-grass or bramble patches in your garden.