Meet the friends on a mouse-saving mission

Eva and Emily (on the right) with some of their friends... and some of their mice!

Would you ever keep a mouse in your bedroom? How about 100 of them?

Well, for the past three years that's exactly what friends Eva and Emily have done at their homes in Devon.

The two 13-year-olds have been working on a plan to help increase the numbers of harvest mice, which are a near threatened species in the UK.

So, they have bred harvest mice in their bedrooms and garages - and this week they got to release them into the wild!

Eva and Emily bred about 100 mice, but they say it's hard to know exact numbers because the tiny mice hide in the straw in their tank!

Eva told Newsround that the mice would sometimes be very noisy when she kept them in her bedroom. They kept her awake at night by "going round and round on their wheels".

After looking after the mice for so long, releasing them back into nature made the teenagers feel a mix of emotions.

Emily says releasing the mice was very "uplifting", and that although she will "miss having them at home... they are wild creatures and should be free".

Eva felt similarly. She was "looking forward to them having their freedom at last" but admitted that seeing the empty tanks made her feel "really sad" that she won't get to see them everyday.

One of Eva and Emily's mice started to forage for food as soon as it was released

Harvest mice are Britain's smallest rodent, they grow to around 50-70mm.

They live in long grassland, reed beds, hedgerows and around woodland edges.

The Mammal Society says harvest mice used to live all over the UK, but now there are fewer of them because farming practices have changed, which has led to their natural homes disappearing.

This is why Eva and Emily have worked so hard to breed the tiny mice, so that they can live in a new wildlife recovery zone and multiply!

Friends Eva and Emily were joined by broadcaster and environmental campaigner Chris Packham on release day

To make sure the harvest mice are able to live happily in their new home, Eva and Emily did lots of preparation.

They fundraised to buy a soft release enclosure, which is a temporary pen that will allow the mice to get used to their new surroundings and develop survival skills.

With other members of their community, Eva and Emily also planted cocksfoot grass (which they say is the mice's favourite for building their nests) and dug a pond to provide water for the creatures when they are living freely.

But despite this project only just finishing, the friends are eager to start the next one.

With 27 empty tanks between them, Emily told Newsround that they are interested in breeding another native species in the future:

"Maybe glow worms or lizards but it's only an idea at the moment."

Watch this space to see what Eva and Emily get up to next!