Arsonists are believed to have caused a "devastating" fire at a nature reserve, destroying an important nesting area for birds and other wildlife.
The blaze broke out at the RSPB Dee Estuary nature reserve at Denhall Quay, Wirral.
A patrolling warden said four youths were seen fleeing the scene, and a police investigation is under way.
The fire, on 8 April, has now been discovered to have killed rare harvest mice and incinerated birds' nests.
RSPB staff said arson attacks on the site have been a problem for "a number of years".
'Important breeding ground'
Site manager Colin Wells said: "The harvest mice have lost their habitat and many of them may have been injured or killed.
"The area is an important breeding ground for birds such as reed buntings and water rails. They have lost their nesting areas.
"It's devastating, as we work so hard to create and maintain this site for wildlife and people to enjoy."
The fire broke out about the same time as a blaze in Heysham, Lancashire which threatened rare butterflies.
Harvest mice have become rare in the UK due to an increasing loss of field margins, hedgerows and grassland habitats.
Cheshire Police have appealed for anyone with information to contact the force.