Can a diet change help water voles back to rivers?

There is hope a diet change for an endangered mammal can help smooth the transition between captivity and the wild.

Water voles were a common sight at the start of the 20th Century and inspired the character Ratty in The Wind in the Willows, but their numbers have plummeted.

The voles are bred near Brecon in Powys and food is being grown using an innovative system involving fish poo and nutrient water in order to prepare them for life once they are released.

Richard Davies from Natural Resources Wales (NRW) said he hoped it would give the creatures a better chance once released into the River Thaw near Cowbridge, Vale of Glamorgan.

Water voles were common in the rivers and waterways of Wales and the rest of the UK decades ago, but their population has dropped by almost 90% since the 1980s, according to People's Trust for Endangered Species.

This is due to a combination of habitat loss and being eaten by predators, including the American mink, introduced to the UK about a century ago because of the demand for fur coats.

NRW, the Wildlife Trust of South and West Wales (WTSWW) and other organisations are working on a project to bring water voles back.

The water voles are bred at a hatchery near Brecon

Staff and volunteers at NRW's Cynig hatchery, where the voles are bred, closely monitor their diet and grow food in a polytunnel using an aquaponics system, where the plants grow in nutrient-rich water rather than soil.

The water is taken from the large fish tanks at the breeding centre which includes the nutrients from the fish poo, which helps the plants to grow more quickly.

Mr Davies, NRW's project leader, said voles were known to feed on more than 200 different species of plants which, until now, had been difficult to feed them in captivity, so the project has been using apples and carrots instead.

He said being released "can be a stressful procedure".

"In the wild, the (water voles) are going to come across tougher grasses and roots, and apples and carrots are not going to be available," he said.

"If you put a complete dietary change in the mix as well, then that can cause even more stress.

"By introducing their natural foods from the aquaponics polytunnel, I think it'll give them a better chance in the wild and be better for their gut health."

The project is releasing voles into the River Thaw near Cowbridge

To learn what water voles like eating, the project staff put small cameras in their enclosures to monitor their choices.

Mr Davies said: "The voles' favourite plants are sedge, water mint, flag iris, and all these species grow very well in the polytunnel. And it's what they eat in the location where we're going to be releasing them."

Alice Chapman, conservation officer with the WTSWW, said: "Water voles act as mini ecosystem engineers, creating more varied vegetation structure and species diversity on the riverbanks they occupy.

"Their burrowing behaviour also creates microhabitats for other species."

This is the second year of water vole reintroductions into the River Thaw and Ms Chapman said there were "plenty of signs that they are here and doing well".

So although seeing "Ratty" in the wild may not be as common as in Kenneth Grahame's day, those behind the project hope it may be more likely in the future.