Monitoring dormice provides information for conservation efforts
Conservationists say they are encouraged by research which suggests that a decline in the numbers of dormice is slowing down.
Monitoring found numbers fell by 9% between 2002 and 2008, compared with 31% from 1992 to 2002.
The People's Trust for Endangered Species (PTES) said there was "reason to be optimistic" that conservation efforts were proving effective.
Loss and degradation of woodland and hedgerow habitats have hit numbers.
Once widespread, the dormouse has become extinct across half its range in England.
Under the National Dormouse Monitoring Programme, running since 1988, volunteers have set up nesting boxes and checked them to help build an idea of dormice population.
Some 197 dormouse sites were monitored by volunteers in 2008.
Jim Jones, of the PTES, said: "While the slowdown in the decline is very encouraging, the species is still in decline, so conservation and monitoring efforts remain a priority if dormice are not to disappear from the British countryside."
Most of the woodland areas monitored over the past 21 years have been managed in a "dormouse-friendly" way.
There have also been 16 successful reintroductions of more than 600 dormice in the past 16 years.
Research had shown dormice needed good coppiced hazel woodland, with undergrowth such as brambles, said Mr Jones.
The PTES has been trying to get the message out to landowners on managing their woods for the mammal.
Dormice have been affected by increasingly isolated habitats, preventing them from breeding with other populations, says the trust.
This also hinders them in moving if their habitat is degraded or affected by climate change.
Dormice are particularly prone to climate change as they struggle in wet summers, which prevent them foraging and putting on weight for their hibernation.
Warmer winters mean they do not hibernate properly, and so use up more energy.