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Individual study: Performance of translocated hazel dormice Muscardinus avellanarius in the Mendip Hills, Somerset, England

Published source details

Bright P.W. & Morris P.A. (1994) Animal translocation for conservation: performance of dormice in relation to relase methods, origin and season. Journal of Applied Ecology, 31, 699-708


The hazel dormouse Muscardinus avellanarius, has been extirpated over about half of its British range due to habitat loss and fragmentation. Reintroductions were proposed as part of a dormouse recovery programme. Prior to this, experimental (licensed) translocations were undertaken in a woodland in southwest England, to assess performance of dormice and establish best translocation practices.

Study site: In 1992, in a 70 ha ancient woodland in the Mendip Hills (Somerset), translocations were conducted to assess performance after release in relation to season, release method and origin (captive bred or wild-caught). The wood was of high quality dormouse habitat but only supported a low density of dormice.

Release animals: Translocated captive-bred dormice were born the previous year and larger individuals (>16 g) were selected. Wild caught animals were taken from nest boxes in woodlands of similar structure and botanical composition to the release site. Adult male dormice may be mutually intolerant, so these were released at least 100 m apart (about one home range diameter). Dormice were released in the same groups as they were found in boxes or in which they had been living if captive-bred. Four release methods were used:

1) Early hard release - Between 30 May to 28 June, eight wild dormice were taken from their native site in the morning, fitted with a miniature radio-transmitter, and placed at the release site in the nest box in which they had been captured by 14:00 hours. Nest boxes were fixed to shrubs at about 1.5 m above ground level and food provided on the first night of release. If their body mass decreased by 20% or more (see Radio-tracking and recapture, below), supplementary food (apple, sunflower seeds etc.) was supplied at the box;

2) Late hard release - as ‘early hard releases’ but dormice (10) released between 24 August and 30 September;

3) Soft release - Between 24 August and 30 September six wild-caught dormice were translocated to pre-release wire mesh pens (45 x 50 x 90 cm high). Pens enclosed a shrub stem about 1.5 m above ground, with the dormouse box and some small branches placed inside. After six nights the dormice were fitted with a transmitter and after a further two nights a hole was made in the top of the pen. Food and water were provided throughout the experiment;

4) Captive-bred releases - as ‘soft release’ but using eight captive-bred dormice.

Radio-tracking and recapture: Radio-tracking was undertaken for at least 10 nights (up to 20) following a release, except when animals died or would have died had they not been recaptured and fed. At 10 nights after release, they were captured and weighed (except four hard-released individuals that could not be recaptured for up to 14 nights). Early hard releases were weighed more frequently when it became apparent that they were rapidly losing body weight. After the study the dormice were recaptured and wild-caught animals were returned to their site of capture.

Body beight: Early hard releases lost weight faster than late hard releases (when natural food e.g. autumn berries, was more abundant) but they regained weight when supplementary food was provided. Soft releases showed a weight increase in comparison to dormice hard released at the same time. In contrast, captive-bred releases lost weight compared to soft releases. In pre-release pens, soft releases gained weight while captive bred releases lost weight, both showed only minor weight loss after release.

Distance travelled: Early hard releases travelled an average distance of 119 m/night, late hard releases 292 m/night. Captive-bred releases travelled only 109 m in comparison with, 209 m by wild-caught dormice. Distances travelled by soft and captive-bred releases were much less than on subsequent nights.

Dispersal movements: The distance animals nested from their release point was used as a measure of site fidelity. This was related to time since release, release type and individual. There were significant differences between all release types, except soft and captive-bred releases which both remained close to their release point. Early hard releases moved further (43 m after 10 days) but no more than the radius of an average dormouse home range (67 m for males, 51 m for females). By contrast, six of 10 late hard releases showed dispersal movements beyond the home range (665 m, 324 m, 180 m, 183 m, 269 m and 208 m) from release points after 10 days, but two subsequently returned to within 40 m of their release points.

Nest box use: Hard releases used more nest sites and spent fewer days in their release nest box than soft or captive-bred releases. Boxes were quickly locate and frequently used as nest sites by hard releases. Commencing on day seven of release, three of 13 soft and captive-bred releases nested away from the box in their pre-release pens, the rest continued to use boxes in pre-release pens.

Foraging behaviour: Dormice visited hawthorn Crataegus monogyna (early hard releases), hazel Corylus avellana and oak Quercus robur more than expected from tree abundance and could be explained by the fact that they provided abundant food. However, less common and patchily distributed plants known to be preferred food e.g. honeysuckle Lonicera periclymenum and brambles Rubus spp., appeared not to be located.

Duration of activity: Average duration of activity (time an individual spent away from the nest) of late hard releases was greater than other release types, as was the activity of early hard releases compared with captive-breds. Soft and captive bred releases greatly increased activity duration during the first four days. This was not accompanied by an increase in distance travelled, except between the first and second nights of release. This hints that soft and captive-bred releases progressively spent longer each night foraging for naturally available food, although they all continued to eat supplementary food.

Post-release survival: Dormice found deeply torpid soon after release had lost more than 20% of body weight, were clearly moribund and therefore counted as mortalities. Most of these were revived by feeding. On this basis, survival from the experiment start (released or placed in pre-release pens) to day 10 were: early hard release 4/7 (57%), late hard release 8/10 (80%), soft release 6/6 (100%) and captive-bred release (87%). For most that died, starvation appeared the cause. One dormouse was died after 2 days and one after 18 days, both suspected to be a result of intra-specific conflict.

Conclusion: Soft releases with supplementary feeding and provision of nest boxes would appear to be the best translocation method for dormice.

Note: If using or referring to this published study please read and quote the original paper.