Edible dormouse

The edible dormouse is the largest of all dormice, being around 14 to 19 cm (5.5 to 7.5 in) in head-body length, plus an 11- to 13-cm-long tail. It normally weighs from 120 to 150 g (4.2 to 5.3 oz), but may almost double in weight immediately prior to hibernation. It has a generally squirrel-like body, with small ears, short legs, and large feet. Its fur is grey to greyish-brown in colour over most of the body, while the underparts and the inner surface of legs are white to pale buff; the line of demarcation is rather well defined.[4]

Unlike most other dormice, they have no dark markings on the face, aside from faint rings around the eyes. The tail is long and bushy, with fur slightly darker than that on the body. Front feet have four digits and their hind feet have five. The soles of their feet are naked. Females have from four to six pairs of teats.[4]

The edible dormouse is capable of limited autotomy; if another animal grasps the tail, the skin breaks easily and slides off the underlying bone, allowing the dormouse to escape. The exposed vertebrae then break off and the wound heals over, forming a fresh brush of hair.[4]

The edible dormouse is found throughout much of mainland western Europe. It is also found on a number of Mediterranean islands, including Sardinia, Corsica, Sicily, and Crete.[5] It is rather more sparsely distributed through central Europe and the Balkans, but can be found as far north-east as the upper Volga River. Close to the Volga River where small groups of the species are found at the Zhiguli Mountains, in Russia.[6] They are also found in the Caucasus region, and along the southern coast of the Caspian Sea.[4] Germany has a small population of edible dormice within its borders, ranging from two to six individuals per hectare.[7]

It is also found in scattered populations throughout Thrace, located on the southeastern tip of the European Balkan peninsula. In this region, two subspecies of the edible dormouse are found, G. g. glis and G. g. orientalis. Northern Anatolia has a different subspecies, G. g pindicus.[8]

Map showing approximate distribution of Glis glis in England

A small, isolated population of Glis glis also exists in south-east England. At the turn of the 20th century, the British banker and zoologist Lionel Walter Rothschild kept Glis glis in his private collection in the town of Tring in Hertfordshire; in 1902 some of the animals escaped and reproduced, establishing themselves in the wild as an invasive species.[9] Today, the British edible dormouse population is thought to be 10,000 strong,[10] and Glis glis have been recorded in a 25-kilometre (16-mile) radius of Tring, mostly concentrated to the south and east.[11] The area of distribution has been described as a 200-square-mile (520 km²) triangle between Beaconsfield, Aylesbury, and Luton, around the southeast side of the Chiltern Hills.[12]

Edible dormice inhabit deciduous forests dominated by oak and beech, from sea level to the upper limits of such forests at 1,500 to 2,000 m (4,900 to 6,600 ft). They prefer dense forests with rocky cliffs and caves, but may be found in maquis vegetation, orchards, and urban margins. They have frequently been reported from caves as deep as 400 m (1,300 ft), where they can shelter from predators.[4]

Population densities range from two to 22 individuals per hectare.[13] Females inhabit only very small home ranges, of 0.15 to 0.76 ha (0.37 to 1.88 acres), but males occupy much larger ranges of 0.8 to 7 ha (2.0 to 17.3 acres), with several burrows.[14]

Edible dormice are primarily herbivorous, feeding mainly on berries, apples, and nuts. However, they are adaptable, and have also been reported to eat bark, leaves, flowers, invertebrates, and even eggs. Beech mast, which is rich in energy and protein, is an excellent source of food for young and lactating females.[4] Some dormice are found to have hair and ectoparasite remains in their stomachs, but this is mainly due to accidental ingestion during grooming.[15]

Edible dormice also consume large numbers of beech tree seeds. A single, large, seeding tree within the home range of a dormouse can produce enough resources to support the energy requirements of reproduction. The location and age of a beech tree helps dictate where a population of dormice live, since older trees produce more seeds.[16]

An edible dormouse.

19th century illustration of Myoxus glis from Iconographia Zoologica

Edible dormice are nocturnal, spending the day in nests taken from birds, or located in hollow trees or similar shelter. They are good climbers, and spend most of their time in the trees, although they are relatively poor jumpers. The dormouse uses sticky secretions of plantar glands when they are climbing on smooth surfaces to prevent them from falling.[4] They generally stay in the forest and avoid open areas to any extent.[13] They are not generally social animals, although small groups of closely related adults have occasionally been reported.[17] Many edible dormice mothers form communal nesting areas where they care for their young together.[4]

Communication is partly by sound, with the animals making various squeaks or snuffling sounds, and partly by scent. They leave scent trails from scent glands on their feet, as well as glands at the top of their tails by the anus. They rub their anal region on the ground and places they walk, so traces of the secretion will be left for other dormice,[4] especially during periods of sexual activity.

Edible dormice are active during a six-month period and go into hibernation[13] from roughly October to May, depending on local climatic conditions. They are mostly active in the summer and are active on average 202 min in a 24-hour day, mostly at night.[6] They prepare a den in soft soil or hidden in a cave, and rely on fat reserves to survive through the winter. During hibernation, metabolic rate and body temperature fall dramatically, and the animal may cease breathing altogether for periods up to an hour.[18] In years with low food availability edible dormice can hibernate longer than 11 months.[19]

In the wild, most edible dormice hibernate for three winters, and then die in the fourth while hibernating, when their cheek teeth are worn out to a degree that prevents normal mastication of food.[20]

Their primary predators include owls, foxes, pine martens, and wildcats.[4]

The breeding season is from late June to mid August, but both male and female dormice do not produce every year.[21] Variation in food resources strongly influences reproduction because reproduction is tightly linked to the availability of energy-rich seeds.[22] Therefore, edible dormice breed during the phase of high food availability. Females are able to produce additional young if amino acid-rich foods like inflorescences, unripe seeds, and (or) larval insects, which also increase their numbers by eating the same enriched plant food, are available.[23] An abundance of energy-rich seeds allows newborn dormice to increase their body fat to prepare for their first hibernation.[22] Females reach sexual maturity at 351–380 days old and males significantly lower their body mass during mating season.[24]

Males are not territorial, and may visit the territories of several nearby females to mate, becoming aggressive to any other males they encounter. The male attracts a female by squeaking, then conducts a circular courtship dance before mounting her. During mating season, males lower their body mass and use their body fat reserves to help fuel the energetic costs of reproduction.[24]

Gestation lasts from 20–31 days, and results in the birth of up to 11 young, although four or five are more typical.[4] They develop their fur by 16 days, and open their eyes after around 3 weeks. They begin to leave the nest after around 30 days, and are sexually mature by the time they complete their second hibernation.[4] Compared with similarly sized mammals, they have an unusually long lifespan, and have been reported to live up to 12 years in the wild.[25]

The breeding habits of the edible dormouse have been cited as a possible cause of its unusual pattern of telomere lengthening with age. In humans and other animals, telomeres almost always shorten with age.[26]

Although the edible dormouse is the only living member of its genus, a number of fossil species are also known. The genus Glis first originated in the middle Oligocene, although it did not become common until the Pliocene. By the Pleistocene, only one species, G. sackdillingensis, is known to have survived, and this is likely the ancestor of the modern species, which first appeared in the early to mid-Pleistocene.[4]

Edible dormice that have been isolated on oceanic islands are a prime example of insular gigantism, in which small animals in isolated locations become larger over the course of many generations.[27] Although it is not known why, the number of teats on a female edible dormouse varies across regions of Europe. For example, those in Italy have two to seven, while those in Lithuania have three to six.[28]

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• The Dormouse Hollow