This picture of a languorous dormouse, snoozing its time away and looked down on by everyone around it, sums up the life of one of our most engaging little mammals. Attractive, with its golden brown fur and long, bushy tail and well known from stories such as Carroll's, it is nonetheless rarely seen and little understood. Only two scientific studies appear to have been published about British dormice this century.
Unfortunate though it is, the dormouse is one of nature's ready-made victims. It has exacting ecological requirements which make it vulnerable, particularly to habitat change, as well as to climatic variation. It lives at a low population density and has a very low rate of population increase. And because it hibernates for half of the year (from October to at least April, depending upon the weather) and is mainly nocturnal, it is not an easy creature to study.
Nevertheless, two studies, one on the distribution of the dormouse, the other about its ecological needs, have been published recently. Both are by Dr Paul Bright and Dr Pat Morris of Royal Holloway, University of London - with the collaboration of Dr Tony Mitchell-Jones of English Nature on the distribution survey - and manage finally to shed some light on why the dormouse is so rare.
To plot the distribution of the dormouse, it is no use relying on sighting these six-inch long (from nose to tip of tail) squirrel-like mice. The more productive way is to search for opened hazelnuts in woodland. Dormouse gnawed nuts have a different pattern of marks from those opened other creatures. As a result, the Great Nut Hunt was launched in 1993, with the help of the Countryside Council for Wales and English Nature, and attracted no less than 6,500 participants (people, not dormice). Out of more than 172,000 gnawed nuts, 1,352 were confirmed as dormouse-nibbled, identifying 334 dormouse sites in England and Wales. They have never been known to occur in Scotland.
What the results of the Great Nut Hunt show is how confined to southern Britain this mammal now is. A quarter of its known sites are in Devon and 12 per cent in Dorset, the two counties in which the dormouse is most abundant. Other southern English counties have a scattering, as do the Welsh borders and a few woods in the north, west and south of Wales.
The survey clarifies the extent to which the dormouse's range has contracted. According to the naturalist and illustrator, Archibald Thorburn, writing in 1920, the dormouse was "fairly plentiful in the southern and western counties of England, though rare in the Midlands and Norfolk". It was, he wrote, abundant in parts of Surrey. Not now. It is seemingly extinct in several counties where it was found late last century. Understanding why is the key to trying to hold on to the populations that remain and, maybe, even help them expand.
First, we need to look at its habitat requirements. The three plant species most associated with dormice - hazel, honeysuckle and bramble - are widely distributed throughout Britain in woods, copses and hedgerows. Hazelnuts are the main fattening-up food consumed prior to hibernation. Honeysuckle offers flowers in springtime, with fruits later in the summer, and finely shredded bark which is the favoured nesting material. Bramble is valuable for its late summer and early autumn fruit supply.
"None of these three species is absolutely vital," argue Bright and Morris, "provided suitable substitutes exist, but few very good dormouse sites are without more than one of them." The problem is that in many woods managed primarily for timber, hazel can take up unproductive space while bramble is a nuisance and climbing plants such as honeysuckle are sometimes cut down. In woods grazed by sheep - common in Wales and the north of England - such shrubs struggle to survive.
The structure of a good dormouse wood is important. It needs to have a well-grown, unshaded understorey of shrubs and small trees so that the sunlight encourages plenty of flowers and fruits. Dense woodlands, or planted rows of trees, are anathema for such frugivorous fantasies. Equally important is a variety of shrubs; a wide range of flowering and fruiting times is more likely to offer a suitable menu. Dormice are unable to digest cellulose-rich foods easily, such as leaves, because they lack a large intestine, yet another restriction. Furthermore, the shrub- and small-tree-rich understorey needs to be physically continuous so that dormice can move in the dark from branch to branch without having to touch the ground. Simple really.
For nesting, they often use tree holes and hollows, but sometimes they take over old squirrels dreys or birds' nests. So, an understorey-rich wood, with not too many larger, shade-bearing trees still has to possess older trees because these are most likely to have natural holes.
The hibernation spot is different again - a cool place on the ground, often in a rock crevice, tree stump or rodent burrow. Surprisingly, for such fussy fellows, dormice take avidly to nest boxes which can mimic the tree holes they need for summer nests. In woods short of natural holes, but endowed with the structure and variety of shrubs required, putting up nest boxes could bolster flagging populations.
But, back to the limitations. Dormice don't move over long distances, but exploit food supplies in perhaps one hectare of woodland over a year, harvesting different spots and shrubs as the seasons change. In one night, radio tracking has shown that they may travel between 150 and 300 metres, but no more than 70 metres in a straight line from the nest, relying on the local knowledge they build up of which shrubs have food and which branches interconnect.
Little wonder, then, that woodland loss and the fragmentation of what native woodland remains have reduced substantially the number of dormouse- suitable habitats. A couple of thousand years ago the bulk of lowland Britain was wooded and one can only assume that dormice were much more commonplace.
Today, remnants of this ancient wildwood cover no more than a small percentage of land. Recent plantations of conifers or broad-leaved trees are usually unsuitable for the dormouse which hasn't adapted to the changes we have wrought. The one exception is that they have moved into some hedgerows, especially older ones with a variety of fruiting shrubs and a dense structure. But hedgerows are in decline too; 150,000 kilometres have been lost since 1945. Hedgerows are also often the only physical link between one isolated wood and the next.
Apart from habitat, its other major drawback is the dormouse's population dynamics. Accord-ing to Bright and Morris, the best sites support up to eight dormice per hectare, compared, for instance, with a minimum of 130 bank voles. So small woods have few dormice, making them highly vulnerable if, for instance, woodland management is altered or there is a succession of poor summers for fruit supply. As only one or two youngsters per female are successfully reared each year, the population rises slowly. Perhaps to compensate, dormice can live up to five years - much longer than, say, bank voles, half of which die before they reach four months.
Relatively untouched by predators - probably because they spend their lives in branches and bushes - the dormouse's lifestyle strategy of a long life, low production of youngsters and low population densities is fine in large areas of suitable habitat under stable conditions. But it is the opposite of what it needs to succeed in today's sparse woods, many of which don't provide the structure and menu these fussy mammals need.
One thing it does get right is its lengthy hibernation - a strategy which overcomes winter food shortages. But, ironically, mild winters are probably more of a threat than cold ones, simply because its fat reserves are depleted faster as its metabolic rate rises. Long, mild British winters, albeit with cold spells, may not be in its favour.
More research on the ecology of dormice is going to be necessary. In the meantime, this mammal is starting to get the attention it deserves, courtesy of an action plan agreed by the government and its conservation agencies. The objectives are to maintain and enhance existing populations, improve woodland management to encourage them, and reintroduce them to suitable woods in at least five counties from which they have been lost.
No longer is the dormouse being ignored. Alice would be ever so pleased.Reuse content