In England most dormice are found south of a line between Shropshire and Suffolk. The People’s Trust for Endangered Species (PTES) runs the National Dormouse Monitoring Programme (NDMP) to monitor numbers. This shows that the population has fallen by 51% since 2000. In England dormice are ‘vulnerable’ under Red List criteria and are therefore fully protected under law. In Bromley they occur in low numbers in the more rural parts of the borough. In the Cudham Valley two sites are monitored under the NDMP and another site is checked. There is a third NDMP site in the Biggin Hill Valley. Surveys have also found them in the Downe Valley. One site is checked here but much of the borough remains to be surveyed. Monitoring in recent years has shown numbers to be falling.

Dormice generally live for about 3 years though have been observed to reach 4-5 years in the wild. From spring-autumn they live in trees and scrub, feeding on flowers, pollen, fruit, nuts, young leaves, buds, insects such as aphids and caterpillars and rarely coming down to ground level. They are nocturnal and live at low population densities: 4-10 individuals/hectare (ha) in the best habitat, 2/ha in oak woodland and about 1-3 in conifer woodland. Female dormice generally have a home range of less than 1ha., males will defend slightly larger territories that may overlap several female home ranges. If there is not much food available or if the weather is cold or wet dormice can become torpid, saving energy. In late spring/summer they make breeding nests, typically of honeysuckle and green hazel leaves. Females usually have 1 litter per year, of 4-5 young born with no fur. The babies stay with their mother 6-8 weeks before becoming independent. Juveniles were thought to rarely disperse more than 100m but recent studies have shown that both young and adults will travel 500m or more. In winter dormice hibernate at ground level where the temperature is fairly constant and the humidity is high, often in a nest of woven grasses - in coppice stools, beneath scrub or in wood banks.

Threats to dormice in the London Borough of Bromley

• Loss of habitat: mixed deciduous woodland with trees and scrub of various sizes, species rich hedgerows.
• Fragmentation of habitat: loss and damage to hedgerows which connect favoured habitat.
• Loss of habitat quality due to a reduction in coppicing and reduced small scale tree felling, reduction in species diversity, increased uniformity of age/size of trees and loss of scrub.
• Climate Change: Warmer, wetter winters disrupt hibernation. Changes in weather patterns affect the availability of food (insects, flowers and fruits).
• Disturbance: hibernating dormice are vulnerable to excessive footfall and disturbance.

Conservation status

• Wildlife & Countryside Act 1981: Fully Protected
• NERC Act 2006 (as amended) England Section 41 species
• Priority BAP Species under the UK Post-2010 Biodiversity Framework
• Mammal Society Red List: Vulnerable
• London Priority Species (2019)
• Bromley Priority Species

Actions 2015-2020

• Three sites monitored under licence as part of the NDMP. Results sent to PTES, Natural England and GiGL: two sites in the Cudham Valley, one in Biggin Hill Valley.
• An additional one site in Cudham valley and one site in Downe Valley checked.
• Woodland management for dormice carried out at the two Cudham Valley sites monitored under NDMP.

More information about hazel dormice