Hibernaculum (zoology)

For other uses, see Hibernaculum (disambiguation).

A hibernaculum plural form: hibernacula (Latin, "tent for winter quarters") is a place in which a creature seeks refuge, such as a bear using a cave to overwinter. The word can be used to describe a variety of shelters used by many kinds of animals, for instance, insects, toads, lizards, snakes, bats, rodents, and primates of various classes.

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  An artificial hibernaculum or 'Bug Hotel'
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  A simple burrow, an example of hibernacula used by snakes
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  Gray bats using a natural cave as a hibernacula

Reptiles

This snapping turtle created a hibernacula by burrowing into mud

Many reptiles undergo hibernation or a process called brumation, which is similar to hibernation; both processes require usage of a hibernacula. Staying inside an insulated hibernacula is a strategy to avoid the harsh winter months when the frigid outside temperatures may kill an ectothermic reptile. Brumating reptiles are also safer from predation inside of their concealed and protected hibernacula. Various species of turtles, lizards, and snakes all use hibernacula, the forms of which can vary greatly.

Common snapping turtles generally hibernate for about 6 months from early October to mid April. They live in lakes during their active months, then travel to small offshoot streams to hibernate. Hibernacula are about 100-150 meters away from the main body of the home lake. Most snapping turtles hibernate by burrowing into the banks of alder streams or vegetated streams, but some use other structures such as abandoned beaver dens. These streams are typically less than 0.3 m deep and 0.7 m wide, covered by sunken alder roots or fallen trees, and not covered by ice in the winter. Many animals return to the same stream to hibernate in subsequent years.

Mammals

Columbian ground squirrel outside its hibernaculum

Like other animals, mammals hibernate during seasons of harsh environmental conditions and resource scarcity. As it requires less energy to maintain homeostasis and survive when an individual is hibernating, this is a cost-effective strategy to increase survival rates. Hibernation is usually perceived as taking place during winter, as in the most well-known hibernators bears and bats, but can also occur during the dry season when there is little food or water, as in the mouse lemurs of Madagascar. Given that mammals can spend anywhere from 1–9 months hibernating, their choice in hibernaculum in essential in determining their survival.

Many mammals that use hibernacula are small-bodied creatures, and include marsupials, rodents, and primates, among others. Most of these small-bodied mammals hibernate in simple holes in the ground, though some use complex systems of tunnels and burrows. Mountain pygmy possums in New South Wales, Australia awaken occasionally and leave their hibernacula for up to five days at a time. This occurs most often during the first few months of hibernation, with the possums leaving one hibernacula in favor of another, seemingly in an effort to find the hibernacula with the most suitable microclimate. The reddish-grey mouse lemur also wakes and leaves the hibernacula spontaenously and for brief periods of time. There can be hibernacula differences even within a species. In Columbian ground squirrels, hibernacula size is proportional to the weight of the individual occupying it, with adults having deeper hibernacula than juveniles. Most juveniles choose to hibernate within 20 meters of their mother's burrow; those that don't have higher mortality rates.

Black bear mother and cubs hibernating, utilizing a hibernaculum as a maternity den

Many bears occupy similar hibernacula to smaller mammals, but theirs are, of course, much larger and can vary greatly across and within species. Most black bears excavate dens into a hillside or at the base of a tree, stump, or shrub, but some make dens at the bases of hollow trees, in hollow logs, or in rock caves or cavities. Den resuse is observed in this species, but very rarely. Unlike Columbian ground squirrels, there were no significant den size differences between age or sex classes, except adult males creating larger entrances. Grizzly bears likewise don't show age or sex class differences in den dimensions. Grizzlies prefer hibernacula sites with abundant ground and canopy cover, and abundant sweet-vetch. Polar bears differ from black bears, grizzlies, and other bear species in that only females use hibernacula, which function as maternity dens. Similarly to other species, though, they tend to dig dens into the earth, although their arctic hibernacula are usually covered with snow by the time they emerge.

Bats favor larger hibernacula where large groups may roost together, including natural caves, mines, cellars, and other kinds of underground sites and man-made structures, like ice-houses. Within these hibernacula, the bats are still highly-tuned to environmental factors. Little brown bats in northern latitudes hibernate for up to 8 months during the winter, and leave their roosts in the warm spring weather when insect prey is plentiful again. Bats gauge the outside temperature by being attuned to the airflow at the hibernacula entrance, which is driven by temperature differences between inside and outside the hibernacula, allowing bats to leave when the temperature begins to warm. Some hibernacula are shared between multiple species, such as common pipistrelles roosting with soprano pipistrelles. Behavior other than hibernating can also occur at hibernacula; common pipistrelles produce most of their mating calls and mate with each other in and near their hibernacula.

See also

• Insect hotel
• Dead hedge