In 2004, 240 harvest mice were released on Northumberland Wildlife Trust’s East Chevington site.
However, in the following months and years, surveys and searches didn’t show any signs of mice or nests, which led conservationists to think the reintroduction may not have been successful.
Fast forward to autumn 2019 and, as part of the Catch My Drift project on the reserve, volunteers carrying out grassland surveys discovered two nests on two separate locations on the reserve - all built by descendants from the mice originally released in 2004.
Spurred on by the discovery, this summer a large private donation enabled the project team to release 200 harvest mice onto the East Chevington reserve.
It was hoped that the 185-hectare site with its extensive reed beds would prove a successful breeding ground for the cute animals, which weigh the same as a 10p coin.
This week, the Catch My Drift staff and volunteers spent five hours surveying where the harvest mice had been released in June and August – a painstaking process involving searching for nests made from balls of grass, the size of a tennis ball, hidden amongst a very grassy area.
They were delighted to discover five nests and signs of feeding through remains of seeds no more than 3mm big - never found before, and an indication of an established colony on the site.
Sophie Webster, Catch My Drift project officer, said: “What a fantastic find and so rewarding for the volunteers who spent five hours searching through the grass in the cold.
"To end the year finding 12 nests in two days is just wonderful. We now have six times more nests than ever before, and to find them in such close to the summer release site of the 200 mice shows they have already boosted the breeding population.”
The Catch My Drift venture at East Chevington is a three-year initiative backed by £418,000 from National Lottery players, via The National Lottery Heritage Fund, to improve the reserve’s habitats, species numbers and upgrade access to the Druridge Bay site.