Page 2 - 2006 DT 12 Issues

The Big Sleep All hibernators rouse from sleep mingbirds experience torpor as deep as
at some point for a few hours or days. death on almost any night—even in the
s winter approaches, most No one is sure why because this strat- tropics. Their daytime energy use is so
animals plan ahead. Food is egy uses up precious energy stores. extreme that they cannot afford to fall
Abeginning to get scarce, and Re-warming may normalize chemical below their metabolic budget. This is
for those not especially adapted to the imbalances that could occur in the known as daily torpor or noctivation.
cold, as rabbits and foxes are, there is suspended state. Little brown bats, for They rouse themselves slowly about one
little choice but to get out of town or find example, may hibernate without rous- to two hours before dawn and can warm
another way to survive. Mother Nature ing for many weeks, or they may wake by several degrees per minute.
is nothing if not resourceful. So if you as often as every 12 to 19 days. Some Although hibernation is gener-
can’t fly away or migrate to a warmer small animals store food in their quarters ally associated with cold regions, it is
climate, why not just go to sleep? for these times. Artificially waking an also a common phenomenon in deserts.
Hibernation is nature’s wonder. animal in deep hibernation, however, Short-term torpor for hours or days is
Many animals practice some form of can have serious survival consequences. a thermo-regulation strategy used by
it—mammals, reptiles, birds, aquatic Snow mobiles and all-terrain vehicles kangaroo rats, prairie dogs, ground
animals (including many fish), worms can be loud enough to disrupt the sleep squirrels, and rock squirrels to tough out
and insects. Unlike normal sleep, clas- cycle, causing energy usage to the scarcity of forage during the winter
sic hibernation, or deep torpor, is a skyrocket, possibly leading months. Many desert reptiles and birds,
death-like state. Metabolism slows to to starvation. including rattlesnakes, chuckwallas,
a very low level, and body temperature Most people as- Gila monsters and nightjars, also
and heart rate drop dramatically. In sociate hibernation with practice torpor.
bats, for example, the heart rate of the bears, but bears are not The most famous hiberna-
desert-dwelling western pipistrelle may classic hibernators. In- tor in the Mojave and Sonoran
drop from a high of over 600 beats per stead, they exist in a Deserts, however, is the des-
minute in mid-flight to a low of under 20 long-term torpid state. ert tortoise. When seasonal
beats per minute. The body temperature Their body tempera- temperatures drop, tortoises
of a warm blooded hibernator will fall ture never falls much enter their underground bur-
to almost match the outside temperature. below normal, and al- rows or dens and go into deep
Breathing is virtually undetectable. though heart rate slows, hibernation, or brumation, as
Peripheral blood vessels close down in their brains are active. it is known in reptiles. As cold
the dormant animal, allowing the aortic Bears can often be eas- blooded reptiles, they cannot reg-
blood pressure to remain at normal lev- ily roused and have been ulate their own body temperature
els. A concentration of lipid droplets in known to attain full alertness and must rely on their dens for warmth.
the myocardium not found in non-hiber- within in a few seconds, according to They may venture out on a warm winter
nators allows energy production in the scientists who’ve lived to tell about it. day, but are usually in the ground from
heart. In this suspended state, an animal In fact, some bears don’t hibernate at all October to March, depending on their
will rely on stored body fat accumulated if the food supply is adequate. environment. Like many desert reptiles,
during late summer and fall. The torpid state is a type of hi- desert tortoises thermo-regulate by mov-
Marmots, woodchucks, box turtles, bernation that varies by duration and ing into areas of sun or shade. During
black snakes, garter snakes and toads are season and is often very short-term. It summer’s warmest months, tortoises
a few of the classic hibernators. Until provides a way for animals like skunks spend increasing amounts of time un-
2004, no primate or tropical mammal was and raccoons to power down and con- derground to avoid the heat of the day.
known to hibernate in this way. Animal serve energy by dropping their body This summer version of hibernation is
physiologist Kathrin Dausmann, Philipps temperature to a set-point for a period. called aestivation and helps many small
University of Marburg, Germany dis- The common poor-will can drop its mammals, reptiles, amphibians, earth-
covered that the fat-tailed dwarf lemur temperature to as low as 43 degrees worms and some insects, such as bees, to
of Madagascar will hibernate in its tree- F in short-term torpor if its supply of conserve energy and fluids during times
hole for as long as seven months. flying insects becomes too scarce. Hum- of high temperature and drought.

Page 2 FORRC/January 2006