Hedgerows provide food, shelter and living space for dormice and serve as leafy corridors through which they can disperse. Hedgerow loss and poor management have led to dormice declining by 64% in hedgerows since the 1970’s, leaving them even more isolated in unconnected woodlands. Dormice serve as indicators for biodiversity loss: if they are not present, other species are likely to have been lost too.
Reduced hedgerow continuity and height through intensification of management reduces food and cover for dormice in hedgerows. Hedgerow shrub diversity is also important.
For a dormouse, connectivity means two things. The habitat in which they live needs to have stems, twigs and branches interlinked so that dormice are able to move around to find food and find a mate without coming to the ground.
As young dormice matures, the juveniles need to have woodlands connected by hedges to enable them to disperse in early autumn through the landscape and establish areas of their own. As even small gaps in a hedgerow can be a barrier to dormice dispersal, the more continuous a hedgerow is, the more likely it is to be used by dormice.
Hedgerows form an important link between woodland copses that are too small to support a viable dormouse population on their own. Crucially, they can also support breeding populations independent of other habitats.
Dormice can be quite specific when it comes to which hedge they nest in. They require a diverse range of plant species and only appear to nest in hedges that are left to grow a little larger.
There have been very few studies of dormice in hedgerows. English Nature published ‘Hedgerow management, dormice and biodiversity’ by Bright and Macpherson in 2002 and their conclusions are summarised below:
There has been a 64% decline of dormouse occurrence in hedgerows since the late 1970s to 2000, equating to a red alert decline of 70% over 25 years.
Loss of dormice from hedgerows is of high conservation concern because:
(i) the dormouse is an indicator of biological diversity
(ii) loss from hedgerows, which are dispersal corridors, implies that dormouse populations have become more isolated
(iii) Population densities in hedgerows are as high as the average for woodlands
Extinction of dormice in hedgerows was strongly related to hedgerow size. Smaller hedges would have led to a lower availability of food and cover for dormice.
Dormouse populations in hedgerows reached densities similar to those found nationally in woodlands.
Hedgerow height was the main feature associated with dormouse abundance in hedgerows. Uncut hedgerows were more likely to be occupied by dormice. Cutting a hedgerow on its top had as much impact on dormouse density as cutting on both sides. Thus, intensive hedgerow management clearly has a negative impact on dormouse density.
Hedgerow shrub diversity was also associated with dormouse density. Dormice were indicators of ancient hedgerows and indicators of hedgerow biodiversity.
The abundance of juvenile dormice in hedgerows was related to the distance to ancient woodland. This shows that hedgerows are used by dormice as dispersal corridors.
Frequent, usually annual, cutting of hedgerows prevents the production of nuts and seeds. Annual cutting leads to lower production of buds and fruit than cutting at two or three year intervals.
To maintain a healthy structure, individual hedgerows are best managed according to their lifecycle. All hedgerows will decline structurally if they are managed in the same way for too long, and so their management needs to reflect their life stage and maturity. The free Healthy Hedgerows app is a rapid assessment tool to help pinpoint the location in the lifecycle of each hedge surveyed, and calculate instant management advice accordingly. Find out more about the Healthy Hedgerows app here.
Staggering hedge management, according to their lifecycle, across a network of hedges will ensure the variety of structures needed by both breeding and migrating dormice.
Nesting dormice benefit from the density of hedges managed on a relaxed trimming cycle, such as on a three-year trimming regimen (H5 or H6).
Food resources will be more abundant in hedges uncut for several years such as those in a non-intervention period (H7).
Hedgerows in a landscape between lifecycle stages H5 and H7 will accommodate both nesting and feeding opportunities for hazel dormice.
A top priority is to restore over-trimmed hedgerows (H1-H3) through laying, coppicing, or incremental increase to more beneficial lifecycle stages, so that a majority of hedges in any landscape are in the ‘Dense and well managed’ category.
For hedgerows on a 3-year cutting regime, it is best to cut up to a third in any one year, rather than all. Most of our hedge plants flower and fruit on second year wood, so relaxed trimming cycles help ensure there are always hedges with adequate food within the network. If hedgerows are required to be cut annually, incremental cutting will ensure the hedge continues to produce both flowers and fruits while maintaining hedge density.
When hedges in a non-intervention period (H7) begin to thin at the base, they need to be rejuvenated by laying or coppicing. While hedges can be rejuvenated by coppicing, laying is preferred. Although a laid hedge will temporarily lose dormouse nesting and feeding opportunities, it will still function as a dispersal corridor. When planning to rejuvenate hedgerows, be mindful of landscape connectivity and try not to isolate individual hedges or woodlands.
Even small gaps can act as barriers to dormouse daily activity. Filling hedge gaps and planting new hedges, can create a more complete hedgerow network in the landscape that will be more suitable to dormouse occupancy.
When planting new hedgerows, or filling gaps, use at least five different shrub/tree species. Dormice eat different things throughout the year, so a wide range of species will help ensure there is always food available to them as the seasons change. Use both locally growing species and those with local provenance.
Dormice are highly protected in the UK and it is generally illegal to disturb them without a licence issued by Natural England or Natural Resources Wales (NRW). This means that surveying for dormice using traditional methods, such as nest boxes or nest tubes, is illegal without a licence. A new survey technique has recently been developed for dormice using footprint tunnels where a licence is generally not required.
Please note: the method given below is not considered to be an appropriate level of effort for an ecological consultant to determine the absence of dormice in a hedge; it is however suitable for a conservation purpose.
The following method is recommended:
Check to see if there are known dormouse populations in your county (see map).
The survey should be conducted in a suitable hedgerow.
Follow the PTES guidance on surveying hazel dormice using footprint tunnels.
If you put 20 tunnels into a hedgerow for one month (plus 2 weeks to account for neophobia) you have a 95.6% chance of detecting dormice if they are present.
The Healthy Hedgerows survey provides instant feedback about the health of the hedge and bespoke management advice. The data that you contribute helps us to understand the overall health of hedgerows at a national scale so that we are able to direct our conservation work. Learn more: