How Animals Survive in Cold Conditions
Science of the Cold
One of the commonest questions
asked about animals in Antarctica is how do
they cope with the extreme cold conditions that
are found there?
temperatures averaging below freezing over
the year (usually well below freezing) with a range in
many places around -40°C to +10°C
and highs up to +22°C amongst rocks and
moss banks. Much of Antarctica is a cold
largely featureless icy desert where
positive temperatures are hardly if ever
reached. The temperature of the Antarctic
Ocean that surrounds the continent varies
from -2°C to +2°C over the year, seawater
freezes at -2°C so it can't get any colder
and still be water.
Antarctic birds and mammals
- penguins, whales and seals - are warm blooded
animals and they maintain similar internal
body temperatures to warm blooded animals in
any other climate zone - that is 35-42°C
(95-107°F) depending on the species. They
have to keep high body temperatures to remain
active. These animals are known as
endotherms (endo-inside + therm-heat) as they generate
their heat internally. Antarctica's cold and
wind mean that this heat can very quickly be
lost leading to hypothermia
are ectotherms (ecto-outside) , which means
that they generate so little heat internally
they are dependent on the external environment
to warm them up to a level where their enzymes
function sufficiently well for an active and
functional life. Typically they raise their
temperature by basking in the sun until they
are warm enough to become active. Reptiles and
amphibians do this while invertebrates
are usually small enough to be able to warm up quickly
to the ambient temperature from the air alone
without basking in direct sunlight.
A large ectothermic
Antarctic land animal would never get enough
energy regularly enough from the surroundings
to become sufficiently active once it had cooled.
All Antarctic land animals of any size therefore
need to be warm-blooded to be active. Antarctica
is such an extreme environment that the size
limit for an ectotherm is about 12mm, the size
of the largest fully terrestrial (land) animal
in Antarctica. In other words any animal larger
than this would not be able to warm up enough
to become active before it started to get cold
is a land mass surrounded by a large very cold
ocean, so unlike the Arctic, purely land-dwelling
animals cannot readily migrate in order to leave
the continent in the long, harsh cold and dark
months of the austral winter. The largest purely terrestrial animal found
in Antarctica is a flightless midge around
2-6 mm in length.
All other Antarctic animals are either smaller
than this or migrate spending some of the year
away from the deep south and the extreme cold.
They either swim or fly away - and back again.
Two examples of Antarctica's
largest land animal - the 1mm long wingless
midge Belgica antarctica has to stay
where it is year round (yes they are mating
Why do animals
go to Antarctica in the first place?
may seem very odd at first when you see pictures
of penguins and seals amongst ice strewn oceans
or snow and icefields. Why would any
animal want to be there in the first place at
all? While it's all very picturesque and makes
for nice pictures, it's hardly an inviting place
to be, especially if you are naked and unsupported
(as animals are).
The answer is a huge seasonal supply of food.
Due to upwelling's of deep ocean water bringing
high levels of nutrients to surface layers and
long day length of up to 24 hours for months
on end depending on the latitude, the southern
ocean is highly productive.
starts as phytoplankton, microscopic fast growing
and reproducing plants that live in the top
layer of the ocean. This is eaten by zooplankton
especially Antarctic krill of various Euphausia
species, particularly the species Euphausia superba. There
is literally millions of tonnes of potential food in the Antarctic
Ocean if you are able to catch it and process
it efficiently. Large blue whales for instance
can catch and eat 4 tonnes or more of krill
a day for weeks on end in the summer months.
has a thermal conductivity around 25 times
greater than air when static, with movement
of the water and convection currents, this
can be 50 to 100 greater than air. This
means that you lose heat much quicker in
water than air, but you knew that already.
There is something called the "lower lethal
temperature" which is the temperature at
which an organism dies. This temperature in
water has never been measured for mammals
such as Antarctic seals and whales. Even the
coldest water (-2°C) doesn't result in death
meaning that these animals can live
indefinitely in cold water without suffering
Their skin surface temperature is nearly
identical to the surrounding water, though
at a depth of around 50mm beneath the skin,
the temperature is the same as their core
temperature. This is due to the insulative
properties of a layer of blubber (fat) under
the skin. Blubber insulates in water, fur
and feathers insulate in air.
blush on this chinstrap penguins
flipper is due to blood being
diverted to cool it down on in this
just above freezing point snow
In the air a seals' skin temperature will
often rise as it needs to lose heat due to
the air being less good at reducing
temperature. The skin is well supplied with
blood vessels that can shunt blood to the
surface or deep within by the constriction
or relaxation of tiny muscles that close or
open up blood vessels.
Penguins, seals and whales have flippers and
flukes without blubber that are poorly
insulated though well supplied with blood
vessels, these too can be used to lose heat
when needed. When it is necessary to retain
heat, arteries surrounded by veins act as
"counter current heat exchangers" to ensure
that blood from the body heats blood
returning from the flippers, so retaining
heat in the core and minimizing heat loss
through the flipper or fluke.
Birds have similar counter-current heat
exchangers in their legs so they don't lose
heat when swimming in frigid water. Like the
seals and whales, the muscles required to
operate these are deeper in the warm parts
of the body and movements made via cord-like
that generate heat from within by metabolic
activity (warm blooded).
Generating your own heat from within that is
sufficient to maintain a steady body temperature
requires two elements:
1 - Enough energy taken
in as food to generate the heat.
2 - Anatomical, physiological and behavioural
adaptations to retain the heat generated.
These two are bound tightly together, unless
you can raise and maintain your temperature,
you cannot be active enough to gather food,
so there aren't any large cold blooded
terrestrial animals in polar regions, once
cold they would never get warm again.
How do endotherms (warm
blooded animals) stay
warm in extreme cold?
- All - Most
of all you need to be large to reduce the
loss of heat from your skin.
- All - Extremities
tend to be small to prevent undue heat loss.
- All - You
need to be well insulated, internally immediately
under the skin with stored fat (blubber)
and externally with fur (the best insulation
of all, though useless when wet) or feathers.
- All - Eat
lots of high energy easy to digest food
to keep warm from within. All large animals
(from the smallest birds upwards) in Antarctica
are carnivores. Meat is a more concentrated
energy rich source of food than is vegetable
matter that doesn't grow very well or very
widely in Antarctica except as tiny
plankton in the seas which requires
extreme specialization to gather. Food supply
is the main problem, small animals
cannot eat enough to keep warm in
extreme cold, they lose heat faster than
they can replace it by releasing
energy from food.
- Some -
Huddling together in large or small
groups is a good way of getting
protection from the wind and retaining
warmth, e.g. penguins.
- Some - Whales
- never leave the sea, so little exposure
to extremes of air temperature, then migrating
north when the air temperature drops enough
to freeze the sea.
- Some - Seals
- entering the sea at times of extremely
cold air temperatures and high winds, then
migrating north when the air temperature
drops enough to start making the sea freeze.
- Some - countercurrent
heat exchangers in flippers
and feet means that these parts are kept
at a lower temperature than the rest of
the body to reduce heat loss, blood is
cooled when it enters and warmed up when
it leaves the flipper or foot. e.g.
seals and whales flippers, penguins
flippers and feet.
More about how
penguins stay warm in the cold.
that have to get heat from the outside (ecto
- outside) environment as they cannot generate enough energy from internal
metabolic processes to maintain a stable body
Ectotherms can warm
up by basking (as most reptiles) their
activity is determined by the external temperature,
when it gets cooler, they just slow down
eventually becoming torpid (dormant,
There are no reptiles or amphibians in
Antarctica and very, very few terrestrial
invertebrates compared to the rest of the
world, it is the only continent without ants
The largest land animal in Antarctica is a
wingless fly about 1mm in length, this and other similar
invertebrates are inactive for much of the
time, when the sun comes out and warms them
up, they become active for a few hours as
long as the temperature remains high enough,
cooling down even below freezing point when
it becomes colder. As they are so small,
they can warm up quickly, if they were
larger, they wouldn't have warmed up to
active temperature before the external
temperature started to drop again.
These animals have lives
of temperature dependent stop-start, the stop
part can last for weeks or even months, the
start part can be just a few hours.
They live in and amongst rocks, moss
and other vegetation. Were they any larger or
if they came out into the open, they would be
easy prey for birds, especially if the
temperature dropped causing them to slow
down and become easy prey for warm blooded
The Antarctic Ocean
is cold but the temperature is very stable varying
between -2°C and +2°C over the year.
It can go down to -2°C (actually -1.9°C)
before it freezes because the dissolved salt
reduces the freezing point of sea-water.
The Antarctic Ocean has been at this temperature
for around 20 million years giving plenty of
time for plants and animals that live there
to become adapted to life in temperatures that
would cause most marine animals to simply slow
down to a state of near torpidity.
That they can do this is down to having very
specialized cold temperature adapted enzyme
systems, many Antarctic marine species are as
active at 0°C as their temperate counterparts
are at 20°C. Cool the temperate species
down and it virtually stops - however warm the
Antarctic species up and it soon starts to suffer
finding life at even 5°C difficult and most
probably dying long before reaching 20°C.
Many species of Antarctic fish have
anti-freeze in their blood, not so much
against the temperature per-se as against
touching ice which at low temperatures could
cause a nucleation point making the ice
spread through their cooled bodies.
These anti-freezes are large
glycoprotein molecules that surround any
small ice crystals that may form, so
preventing their spread throughout the
animals tissues which would mean death.
Interestingly only fish that are likely to
encounter ice have these anti-freezes,
deeper living fish way below the level of
floating ice don't have anti-freeze,
they have a freezing point
above that of the sea-water in which they live. They spend their entire lives in
a state of being "supercooled" that is, at a temperature that is below their freezing
temperature. They can do this as they never come into contact with ice crystals
- such fish do not have anti-freeze and live in the depths of the Antarctic ocean
- ice is only found in the upper reaches.
If these fish are brought to the surface where they
can come into contact with ice, the ice will cause a nucleation point that spreads
in their bodies causing instant freezing and death.
ectotherm, poikiliotherm, homeotherm,
heliotherm, warm blooded, cold blooded
There are many words used to describe the ability
of animals to maintain their body temperature.
Some are infrequently used these days but
all are used at some time or other.
The basic distinction is between animals such
as birds and mammals that maintain a stable
core temperature of around 35-42°C irrespective
of the environmental temperature and those whose
temperature is variable, more closely reflecting
the environmental temperature.
The reason that the nomenclature is not straightforward
is that there are animals that refuse to sit
cleanly in one of the two apparent obvious categories.
Some organisms clearly didn't read the rules
and sometimes make bits of themselves warmer
than other bits irrespective of the
ambient temperature or manage to maintain a
stable internal temperature without necessarily
generating that heat internally.
Warm blooded -
Animals that maintain a stable warm core
temperature of around 35-42°C, the
temperature itself usually being closely
monitored, the actual temperature is species
dependent and very precise, 37°C in humans
Endotherm - Animals
that generate heat from within by metabolic
activity, usually this means that they can maintain
a stable core temperature of around 35-42°C.
The term can also apply some of the time to
fish such as tuna that are able to maintain
their active swimming muscles at 20°C or so
above the temperature of the rest of their
body by means of a counter-current heat
exchanger, this keeps the swimming muscle
warm so it works better and prevents heat
loss to the rest of the body.
Homeotherm - homo-same,
therm-heat, an animal that maintains a stable
warm body temperature.
Cold blooded - Animals
that have a body temperature the same as the
environmental temperature and are unable to
warm it above this.
Animals that cannot generate enough energy
from internal metabolic processes to
maintain a stable body temperature, heat
comes from outside of the animal.
An animal whose internal temperature varies
quite considerably (little used any more).
Heliotherm - An
organism that warms itself up by basking in
the direct rays of the sun.
Heterotherm - hetero-other,
therm-heat, an animal that differs in its body
temperature at different times.
It is possible that more than one of these terms
may apply to a particular animal at different
times, which could be daily or annually.