How Animals Survive 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?
averaging below freezing over the year (frequently
significantly 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, though many places are significantly
colder. The sea temperature varies from -2°C
to +2°C over the year.
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
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 (hypo-under).
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 many invertebrates
are 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 1mm, 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 again.
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. This means that
the largest purely terrestrial animal found
in Antarctica is a flightless midge that reaches
a maximum size of 1mm 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. This productivity
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 various Euphausia
species, especially Euphausia superba. There
are piles and piles of 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.
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
2 - Anatomical, physiological and behavioural
adaptations to retain the heat generated.
These two are bound tightly together, unless
you can maintain temperature, you cannot be
active enough to gather food, so there aren't
any large cold blooded terrestrial animals in
How do endotherms 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 anyway. Food supply
is more of a problem than the other aspects
of living in a cold climate, small animals
cannot eat enough to keep warm in extreme
- Some - Huddling
together in large or small groups is a good
way of getting protection from the wind
and retaining warmth.
- Some - Whales
- never leave the sea, so little exposure
to extremes of air temperature, then migrating
north when the air temperature drops enough
to start making the sea freeze.
- 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 seals and whales flippers
and birds feet means that these parts are
kept at a lower temperature than the rest
of the body to reduce heat loss.
More about how
penguins stay warm in the cold.
Animals that cannot generate enough energy from
internal metabolic processes to maintain a sufficiently
high body temperature to be active have to warm
up by basking (as most reptiles), be as active
as they can manage given the temperature they
are or just slow down and become torpid.
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 for example.
As mentioned above, the largest land animals
in Antarctica is a wingless fly, 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.
These animals have lives
of temperature dependent stop-start, the stop
part can last for weeks or even months.
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 when they slowed
down to a stop and couldn't run away.
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
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.
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.
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 no longer used so often but it seems
that 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 utterly 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.
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,
but 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.
Homeotherm - homo-same, therm-heat, an animal that maintains a stable
warm body temperature.
Cold blooded - Animals
that have a body temperature colder than the
environmental temperature, though not necessarily
all of the time.
Ectotherm - Animals
that cannot generate enough energy from internal
metabolic processes to maintain a stable body
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.