Hibernation is a state of inactivity and
metabolic depression in
animals, characterized by lower body temperature,
slower breathing, and lower metabolic rate. Hibernating animals
conserve
energy, especially during winter
when food is short, tapping energy reserves,
body fat, at a slow rate. It is the animal's slowed
metabolic rate which leads to a reduction in body temperature and
not the other way around.
Hibernation may last several days or weeks depending on species,
ambient temperature, and time of year. The typical winter season
for a hibernator is characterized by periods of hibernation
interrupted by sporadic
euthermic arousals
wherein body temperature is restored to typical levels. There is a
hypothesis that hibernators build a need for sleep during
hibernation more slowly than normally, and must occasionally warm
up in order to sleep. This has been supported by some evidence in
the arctic
ground squirrel.
Hibernating animals
Animals that hibernate include
bats, some
species of
ground squirrels and
other
rodents,
mouse
lemurs, the
West European
Hedgehog and other
insectivores,
monotremes and
marsupials. Even some
rattlesnakes, such as the
Western Diamondback, are known to hibernate
in caves every winter. Historically,
Pliny the Elder believed that
swallows hibernated, and ornithologist
Gilbert White pointed to anecdotal evidence in
The Natural History of Selborne that indicated as much.
Birds typically do not hibernate, instead utilizing
torpor. However the
Common
Poorwill does hibernate. Many experts believe that the
processes of daily
torpor and hibernation
form a continuum.
One animal that some famously consider a hibernator is the
bear, although bears do not go into "true hibernation".
During a bear's winter sleep state, the degree of metabolic
depression is much less than that observed in smaller mammals. Many
prefer to use the term "
denning". The bear's body
temperature remains relatively stable (depressed from to
approximately ) and it can be easily aroused. Some reptile species
are said to brumate, or undergo
brumation,
but the connection to this phenomenon with hibernation is not
clear.
Hibernating ground squirrels may have abdominal temperatures as low
as , maintaining sub-zero abdominal temperatures for more than
three weeks at a time, although the temperatures at the head and
neck remain at 0 C or above.Before entering hibernation most
species eat a large amount of food and store energy in fat deposits
in order to survive the winter. Some species of mammals hibernate
while
gestating young, which are born
shortly after the mother stops hibernating.
Hibernating animals get their energy by a biochemical process known
as
gluconeogenesis.
For a
couple of generations during the 20th century it was thought that
basking sharks settled to the floor of
the North
Sea
and hibernated; however, research by Dr David Sims
in 2003 dispelled this hypothesis, showing that the sharks actively
traveled huge distances throughout the seasons, tracking the areas
with the highest quantity of plankton.
The
epaulette sharks have been
documented to be able to survive for long periods of time without
oxygen, even being left high and dry, and at temperatures of up to
. Other animals able to survive long periods without oxygen include
the
goldfish, the
red-eared slider turtle, the
wood frog, and the
bar-headed goose.
Until recently no
primate, and no
tropical mammal, was known to
hibernate.
However, animal physiologist Kathrin Dausmann of Philipps
University of Marburg
, Germany
, and
coworkers presented evidence in the 24 June
2004 edition of Nature that the Fat-tailed Dwarf Lemur of Madagascar
hibernates in tree holes for seven months of the year.
This is
interesting because Malagasy
winter
temperatures sometimes rise to over , so hibernation is not
exclusively an adaptation to low ambient temperatures. The
hibernation of this lemur is strongly dependent on the thermal
behavior of its tree hole: if the hole is poorly insulated, the
lemur's body temperature fluctuates widely, passively following the
ambient temperature; if well insulated, the body temperature stays
fairly constant and the animal undergoes regular spells of arousal.
Dausmann found that
hypometabolism in
hibernating animals is not necessarily coupled to a low body
temperature.
Noise and vibration from snowmobiles,
all-terrain vehicles (ATV) and the like
is said to sometimes awaken hibernating animals, who may suffer
severely or die as a result of premature awakening in times of food
shortage. However, many hibernators can return to hibernation after
awakening, and deep hibernators in fact awaken many times
throughout the hibernation season in what are called interbout
arousals.
Artificial hibernation
There are many research projects currently investigating how to
achieve "induced hibernation" in humans. The ability for humans to
hibernate would be useful for a number of reasons, such as saving
the lives of seriously ill or injured people by temporarily putting
them in a state of hibernation until treatment can be given
(compare
induced coma).
NASA
is also
interested in possibly putting astronauts in hibernation when going
on very long space journeys, making it possible one day to visit other stars.
See also
References
- Jaeger, E.C. 1948. "Does the poorwill hibernate?"
Condor 50:45-46.
- Secrets of Hibernation; nova, pbs.org
- Breathless: A shark with an amazing party trick is
teaching doctors how to protect the brains of stroke patients.
Douglas Fox, New
Scientist vol 177 issue 2385 - 8 March 2003, page 46. Last
accessed November 9, 2006.
- Hibernation
- Times Online
Further reading
- Carey, H.V., M.T. Andrews and S.L. Martin. 2003. Mammalian
hibernation: cellular and molecular responses to depressed
metabolism and low temperature. Physiological Reviews 83:
1153-1181.
External links
Wikis
Quiz
Facts
Map
Misc
Search
