Encyclopaedia Britannica, 11th Edition, "Hero" to "Hindu Chronology" / Volume 13, Slice 4

by Various

Amongst the Rodentia, no members of the Lagomorpha (hares, rabbits and picas) are known to hibernate, although some of the species, like the mountain hare (Lepus timidus), extend far to the north in the palaearctic region, and the picas (Ochotona) live at high altitudes in the Himalayas and Central Asia, where the cold of winter is excessive, and where the snow lies deep for many months. It is probable that the picas live in fissures and burrows beneath the snow, and feed on stores of food accumulated during the summer and autumn. The Hystrico-morpha also are non-hibernators. It is true that the common porcupine (Hystrix cristata) of south Europe and north Africa is alleged to hibernate; the statement cannot, however, be accepted without confirmation, because the cold is seldom excessive in the countries it frequents, and specimens exhibited in the Zoological Gardens in London remain active throughout the year, although kept in enclosures without artificial heat of any kind. Even the most northerly representative of this group, the Canadian porcupine (Erethizon dorsatus), which inhabits forest-covered tracts in the United States and Canada, may be trapped and shot in the winter. Some members of this group, like capybaras (Hydrochaerus capybara) and coypus (Myocastors coypus) which live in tropical America, are unaffected by the winter cold of temperate countries, and live in the open all the year round in parks and zoological gardens in England. Several of the genera of Myomorpha contain species inhabiting the northern hemisphere, which habitually hibernate. The three European genera of dormice (Myoxidae), namely Muscardinus, Eliomys and Glis, sleep soundly practically throughout the winter; and examples of the South African genus Graphiurus practise the same habit when imported to Europe. If a warm spell in the winter rouses dormice from their slumbers, they feed upon nuts or other food accumulated during the autumn, but do not as a rule leave the nests constructed for shelter during the winter. According to the weather, the sleep lasts from about five to seven months. In the family Muridae, the true mice and rats (Murinae) and the voles and lemmings (Arvicolinae) seem to remain active through the winter, although some species, like the lemmings, range far to the north in Europe and Asia; but the white-footed mice (Hesperomys) of North America, belonging to the Cricetinae, spend the winter sleeping in underground burrows, where food is laid up for consumption in the early spring. The Canadian jumping mouse (Zapus hudsonianus), one of the Jaculidae, also hibernates, although the sleep is frequently interrupted by milder days. Some of the most northerly species of jerboas (Jaculidae), namely Alactaga decumana of the Kirghiz Steppes and A. indica of Afghanistan, sleep from September or October till April; and the Egyptian species (Jaculus jaculus) and the Cape jumping hare (Pedetes caffer), one of the Hystrico-morpha, remain in their burrows during the wet season in a state analogous to winter sleep. The sub-order Sciuromorpha also contains many hibernating species. None of the true squirrels, however, appear to sleep throughout the winter. Even the red squirrel (Sciurus hudsonianus) of North America retains its activity in spite of the sub-arctic conditions that prevail. The same is true of its European ally Sc. vulgaris. The North American grey squirrel (Sc. cinereus), although more southerly in its distribution than the red squirrel of that country, hibernates partially. Specimens running wild in the Zoological Gardens in London disappear for a day or two when the cold is exceptionally keen, but for the most part they may be seen abroad throughout the season. On the other hand, ground squirrels like the chipmunks (Tamias) and the susliks or gophers (Spermophilus) of North America and Central Asia, at all events in the more northern districts of their range, sleep from the late autumn till the spring in their subterranean burrows, where they accumulate food for use in early spring and for spells of warmer weather in the winter which may rouse them from their slumbers. The North American flying squirrel (Sciuropterus volucella) and its ally Pteromys inornatus are believed to hibernate in hollow trees. All the true marmots (Arctomys), a genus of which the species live at tolerably high altitudes in Central Europe, Asia and North America, appear to spend the winter in uninterrupted slumber buried deep in their burrows. They apparently lay up no store of food, but accumulate a quantity of fat as the summer and autumn advance, and frequently, as in the case of the woodchuck (A. monax) of the Adirondacks, retire to winter quarters in the autumn long before the onset of the winter cold. The prairie marmots or prairie dogs (Cynomys ludovicianus) of North America, which live in the plains, do not hibernate to the same extent as the true marmots, although they appear to remain in their burrows during the coldest portions of the winter. Beavers (Castor), although formerly at all events extending in North America from the tropic of Cancer up to the Arctic circle, do not hibernate. When the ground is deep in snow and the river frozen over, they are still able to feed on aquatic plants beneath the ice.

Amongst the terrestrial carnivora hibernation appears to be practised, with one possible exception, only by species belonging to the group Arctoidea. In north temperate latitudes both in Europe and Asia, as well as in the Himalayas, brown bears (Ursus arctos) hibernate, so also does the North American grizzly bear (U. horribilis), at least in the more northern districts of its range. The smaller black bear of the Himalayas (U. tibetanus) appears to lapse into a state of semi-torpor during the winter, only emerging from his retreat to hunt for food when occasional breaks in the weather occur. In the case of the American black bear (U. americanus) the female seeks winter quarters comparatively early in the season in preparation for the birth of her progeny soon after the turn of the year; but the males remain active so long as plenty of food is to be found. In the case of all bears, except the Polar bear (U. maritimus), the site chosen as the hibernaculum is either a cave or hole or some sheltered spot beneath a ledge of rock, or the roots of large trees, more or less overgrown with brushwood which holds the snow until it freezes into a solid roof over the hollow where the sleeping animal lies. In the hibernating brown and black bears the intestine is blocked by a plug commonly called “tappen” and composed principally of pine leaves, which is usually not evacuated until the spring. There is much diversity of opinion on the subject of the hibernation of Polar bears. Their absence during the winter from particular spots in the Arctic regions where icebound ships have spent the winter, and the occasional discovery of specimens buried beneath the snow, have led to the belief that these animals habitually retire to winter quarters through the cold sunless months of the year. This may possibly be the true explanation at least for certain districts. But it has been alleged that bears, both adult and half-grown, may be seen throughout the winter; and it is known that pregnant females bury themselves in the autumn under the snow, where they remain without feeding with their newly-born young until the spring of the following year. Hence the absence of bears in the winter from the neighbourhood of icebound ships may be explained on the supposition that the adult females alone hibernate for breeding purposes, while the full-grown males and half-grown specimens of both sexes migrate in the winter to the edges of the ice-floes and to coast lines, where the water is open. Before retiring to winter quarters the pregnant females store up sufficient quantity of fat in their tissues not only to sustain themselves but also to supply milk for their cubs. In the Adirondack region and probably in other districts of the same or more northern latitudes in North America, raccoons (Procyon lotor) retire in the winter to some sheltered place, such as a hollow tree-trunk, and pass the severest part of the season in sleep, emerging in February or March when the snow has begun to disappear. In the same country, the skunks (Mephitis mephitica), a member of the weasel family, also seek shelter during the coldest portion of the winter. Merriam believes that the hibernation of this animal is determined by cold, and not by failure of food-supply, for he observes that skunks may frequently be seen in numbers on snow lying 5 ft. deep at a time of the year when they feed almost entirely upon mice and shrews which do not hibernate even when the thermometer registers over twelve degrees of frost. In British North America the badger (Taxidea americana) is said to hibernate from October till April; but the duration of the period probably depends, as in the case of its European ally (Meles meles), upon the length and severity of the inclement season. In the last-named species the winter repose is not as a rule sufficiently profound to prevent a break in the weather rousing the animal from sleep to sally forth in search of food. This interrupted hibernation takes place at least in England and even in Scandinavia; but in countries where frost is continuous throughout the winter it is probable that the badger’s sleep is unbroken.

The one exception to the general rule that hibernation in the Carnivora is restricted to the Arctoidea, is supplied by the raccoon dog (Nyctereutes procyonoides) of Japan and north-eastern Asia, which is said by Radde to hibernate in burrows in Amurland if food has been sufficiently plentiful in late summer and autumn to enable the animal to lay on enough fat to resist the cold and sustain a long period of fast. If, however, food has been scarce, this dog is compelled to remain active all through the winter. The Arctic fox (Vulpes lagopus), although considerably more northern in range than the raccoon dog, does not hibernate. It was long a mystery how these animals obtained food in winter, but it has been ascertained that in some districts they migrate southwards in large numbers in the late autumn, whereas in other districts apparently they lay up stores of dead lemmings or hares, for food during the winter months. In Australia the porcupine ant-eater (Echidna aculeata) hibernates; and the habit is retained by specimens imported to Europe if exposed to the cold in outdoor cages.

Instances of quasi-hibernation have been recorded in the case of man. For example, in the government of Pskov in Russia, where food is scarce throughout the year and in danger of exhaustion during the winter, the peasants are said to resort to a practice closely akin to hibernation, spending at least one-half of the cold weather in sleep. From time immemorial it has been the custom when the first snows fall for families to shut themselves up in their huts, huddle round the stove and lapse into slumber, each member taking his turn to keep the fire alight. Once a day only do the inmates rouse themselves from sleep to eat a little dry bread.

Reptiles in which the body-temperature falls with that of the surrounding medium pass the winter in temperate countries in a state of lethargy; and specimens exported from the tropics into northern latitudes become dormant when exposed to cold in virtue of their inability to maintain their temperature at a higher level than that of the atmosphere. The common land tortoise (Testudo graeca) of South Europe buries itself in the soil during the winter in its natural habitat, and even when imported to England is able, in some cases at least, to withstand the more rigorous winter by practising the same habit, as Gilbert White originally recorded. In Pennsylvania the box-tortoise (Cistudo carolina) passes the winter in a burrow; and Testudo elegans, which inhabits dry hilly districts in north India, takes shelter beneath tufts of grass or bushes as the cold weather approaches and remains in a semi-lethargic state until the return of the warmth. The European pond tortoise (Emys orbicularis) also hibernates buried in the soil; and the North American salt-water terrapin (Malacoclemmys concentrica), abundant in the salt-marshes round Charleston, S. Carolina, retires into the muddy banks to spend the cold months of the year. In certain parts of the tropics tortoises protect themselves from the excessive heat by burrowing into the soil which afterwards becomes indurated. When drought sets in with the dry season and the tanks become exhausted and food unobtainable, crocodiles and alligators sometimes wander across country in search of water, but more commonly bury themselves in the mud and remain in a state of quiescence until the return of the rains; and according to Humboldt, large snakes, anacondas or boa constrictors are often found by the Indians in South America buried in the same lethargic state. Snakes and lizards in all countries where there is any considerable seasonal variation in temperature become dormant or semi-dormant during the colder months.

Batrachians, like reptiles, hibernate in Europe and other countries situated in temperate latitudes. Frogs bury themselves in the mud at the bottom of tanks and ponds, often congregating in numbers in the same spot. Toads retire to burrows or other secluded places on the land, and newts either bury themselves in the mud of ponds, like frogs, or lie up beneath stones and pieces of wood on the land. According to Mr G. A. Boulenger, however, European frogs and toads do not pass the winter in profound torpor, but merely in a state of sluggish quiescence. In tropical countries, where wet and dry seasons alternate, frogs which, like the rest of the batrachians, are for the most part intolerant of great heat, especially when accompanied by dryness of atmosphere, bury themselves deep in the soil during the time of drought and emerge from their retreats in numbers with the breaking of the rains.

This habit of passing the dry season in the hardened mud forming the bottom of exhausted pools and rivers is practised by several species of tropical freshwater fishes, belonging principally to the family Siluridae. The members of this group are able to exist and thrive in moist mud, and can even support life for a comparatively long time out of water altogether. The instinct is exhibited by species occurring both in the eastern and western hemispheres, as is shown by its record in the case of species of Callicthys and Loricaria in Guiana and by Clarias lazera in Senegambia. It is also met with, according to Tennent, in a species of climbing perch (Anabas oligolepis) found in Ceylon and belonging to the family Anabantidae, all the species of which are able to live for a certain length of time out of water, and may sometimes be found crawling across land in search of fresh pools. The habit is also common to some species of mud fishes of the order Dipneusti, in which the air bladder plays the part of lungs. Protopterus, from tropical Africa, for instance, burrows into the mud and remains for nearly half the year coiled up at the bottom in a slightly enlarged chamber. The walls of this are lined with a layer of slime secreted from the fish’s skin, and the orifice is closed with a lid the centre of which is perforated and forms an inturned tube by means of which air is conducted to the fish’s mouth. The aestivating burrow of the Brazilian mudfish (Lepidosiren) is similar, except that the lid is perforated with several apertures. The Australian mudfish (Ceratodus) is not known to hibernate or aestivate.

In countries where winter frosts arrest the growth of vegetation terrestrial mollusca seek hibernacula beneath stones or fallen tree trunks, in rock crannies, holes in walls, in heaps of dead leaves, in moss or under the soil, and remain quiescent until the coming of spring. Amongst pulmonate gastropods, most species of snails (Helix, Clausilia) close the mouth of the shell at this period with a membranous or calcified plate, the epiphragm. Slugs (Limax, Arion), on the contrary, lie buried in the earth encysted in a coating of slime. Similarly in the tropics members of this group, such as Achatina in tropical Africa and Orthalicus in Brazil, aestivate during the dry season, the epiphragm preserving them against desiccation; and examples of two species of Achatina from east and west Africa exhibited in the Zoological Gardens in London remained concealed in their shells during the winter, although kept in an artificially warmed house, and resumed their activity in the summer.

Freshwater Pulmonata do not appear to hibernate, such forms as Limnaea and Planorbis having been frequently seen crawling about beneath the ice of frozen ponds. During periods of drought in England, however, they commonly bury themselves in the mud, a habit which is also practised during the dry season in the tropics by species of Prosobranchiate Gastropods belonging to the genera Ampullaria, Melania and others, which lie dormant until the first rains rouse them from their lethargy. Freshwater Pelecypoda (Anodonta, Unio) spend the European winter buried deep in the muddy bottom of ponds and streams.