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2. What is torpor???
 Torpor is a state of decreased physiological activity in an animal, usually by a
reduced body temperature and metabolic rate.
 Torpor enables animals to survive periods of reduced food availability.
 The term "torpor" can refer to the time a hibernator spends at low body
temperature, lasting days to weeks, or it can refer to a period of low body
temperature and metabolism lasting less than 24 hours, as in "daily torpor".

3.  Animals that undergo daily torpor include birds (even tiny hummingbirds, notably
Cypselomorphae) and some mammals, including many marsupial species, rodent
species (such as mice), and bats.
 During the active part of their day, such animals maintain normal body
temperature and activity levels, but their metabolic rate and body temperature
drops during a portion of the day (usually night) to conserve energy.
 Torpor is often used to help animals survive during periods of colder
temperatures, as it allows them to save the energy that would normally be used to
maintain a high body temperature.

4.  Some animals seasonally go into long periods of inactivity, with
reduced body temperature and metabolism, made up of multiple
bouts of torpor.
 This is known as hibernation if it occurs during winter or
aestivation if it occurs during the summer.
 Daily torpor, on the other hand, is not seasonally dependent and
can be an important part of energy conservation at any time of
year.

5.  Torpor is a well-controlled thermoregulatory process and not, as previously thought,
the result of switching off thermoregulation.
 Marsupial torpor differs from non-marsupial mammalian (eutherian) torpor in the
characteristics of arousal. Eutherian arousal relies on a heat-producing brown adipose
tissue as a mechanism to accelerate rewarming.
 The mechanism of marsupial arousal is unknown, but appears not to rely on brown
adipose tissue.

6. Evolution
 The evolution of torpor likely accompanied the development of homeothermy.
 Animals capable of maintaining a body temperature above ambient temperature
when other members of its species could not would have a fitness advantage.
 Benefits of maintaining internal temperatures include increased foraging time and
less susceptibility to extreme drops in temperature.
 This adaptation of increasing body temperature to forage has been observed in
small nocturnal mammals when they first wake up in the evening

7.  Although homeothermy lends advantages such as increased activity
levels, small mammals and birds maintaining an internal body
temperature spend up to 100 times more energy in low ambient
temperatures compared to ectotherms.
 To cope with this challenge, these animals maintain a much lower body
temperature, staying just over ambient temperature rather than at normal
operating temperature.
 This reduction in body temperature and metabolic rate allows the
prolonged survival of animals capable of entering torpid states.

8. Function
1) In times of insufficient resources is the primarily noted purpose of torpor.
2) This conclusion is largely based on laboratory studies where torpor was
observed to follow food deprivation.
3) There is evidence for other adaptive functions of torpor where animals are
observed in natural context of small migrant birds to increase their body
fat.
4) Hummingbirds, resting at night during migration, were observed to enter
torpor which helped conserve fat stores for the rest of their migration.

9. Fat conservation in small birds
 This strategy of using torpor to increase body fat has also been observed in wintering
chickadees.
 Black-capped chickadees, living in temperate forests of North America, do not migrate
south during winter.
 The chickadee can maintain a body temperature 12 °C lower than normal. This
reduction in metabolism allows it to conserve 30% of fat stores amassed from the
previous day.
 Without using torpor the chickadee would not be able to conserve its fat stores to
survive winter.

10. Advantage in environments with unpredictable food sources
 Torpor can be a strategy of animals with unpredictable food supplies.
 For example, high-latitude living rodents use torpor seasonally when not reproducing.
 These rodents use torpor as means to survive winter and live to reproduce in the next reproduction cycle
when food sources are plentiful, separating periods of torpor from the reproduction period.
 Some animals use torpor during their reproductive cycle, as seen in unpredictable habitats.
 They experience the cost of a prolonged reproduction period but the payoff is survival to be able to
reproduce at all.
 The eastern long-eared bat uses torpor during winter and is able to arouse and forage during warm
periods.

11. Parasite resistance by bats
 A drop in temperature from torpor has been shown to reduce the ability of parasites to
reproduce.
 Ectoparasites of bats in temperate zones have reduced reproductive rates when bats enter torpor.
 Where bats do not enter torpor the parasites reproduce at a constant rate throughout the year.