The hazel dormouse is famous for spending much of the year asleep. It hibernates from around October to May, spending the winter in a nest on the ground.
Even during spring and summer, dormice can go into short periods of deep sleep, known as torpor, when the weather is cold and wet, or food is scarce. This helps the small rodent conserve energy.
Researchers believe warmer summers may be reducing the need for torpor, leaving dormice with more energy for feeding and breeding.
They say more research is needed to understand what longer-term impacts climate change could have on the species.
Dr Charlotte Armitage, an ecologist who worked on the survey, said significant uncertainties remain, including how dormice will respond to warmer, wetter winters.
However, she said warmer summer conditions are likely to give the animals more energy to reproduce and raise additional litters.
“This is good news, but we can’t be complacent,” she told BBC News.
“We still need to protect their habitat, do more research into the effects of climate change and carry out effective woodland management for the benefit of dormice.”