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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?

The problem


Emperor penguins breed in the depths of the Antarctic winter


Weddell seals swim in water that is 2 degrees either side of zero, the air temperature when they leave the sea is often a lot colder
Air 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 above freezing temperatures are hardly reached if ever at all. 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 (hypo-under).

Many animals 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 body and enzymes function sufficiently well enough 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 again.

Migration

Antarctica 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 that grows no more than 13mm 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 13mm long wingless midge Belgica antarctica has to stay where it is year round (yes they are mating - snigger).

Why do animals go to Antarctica in the first place?

It may seem very odd at first when you see pictures of penguins and seals amongst ice strewn oceans or snow and ice fields.

Why would any animal want to be there at all? While it's all very picturesque and makes for nice photos and videos, it's hardly an inviting place to be, especially if you don't have any shelter or support (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 exceptionally productive.

This productivity starts as phytoplankton, microscopic fast growing and reproducing plants that live in the top layer of the ocean. These are eaten by zooplankton especially Antarctic krill of various Euphausia species, particularly the species Euphausia superba (pictured).

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.

Air or Water


The pink blush on this chinstrap penguins flipper is due to blood being diverted to cool it down on in this just above freezing point snow flurry
Water has a thermal conductivity around 25 times greater than air when still, 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, which you probably knew 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 because it can't. Even the coldest water (-2C) doesn't result in death meaning that these animals can live indefinitely in cold water without suffering from hypothermia.

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 insulating properties of a layer of blubber (fat) under the skin. Blubber insulates in water, fur and feathers insulate in air.

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 tendons.


Rockhopper flipper showing how little muscle there is with tendons which attach to muscles that are deeper in the penguins body to prevent heat loss

Endotherms and the cold

Endotherm - Animals that generate heat from within by metabolic activity (warm blooded).

Killer whale or Orca looking around having broken thin ice for a breathing hole, picture courtesy NOAAGenerating your own heat from within that is sufficient to maintain a steady body temperature requires two elements, making warmth and then hanging onto it.

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 generate warmth 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 and dolphins - 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.

Ectotherms and the cold

Ectotherm - Animals 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 temperature.

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, inactive).

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.

The largest land animal in Antarctica is a wingless fly about 13mm 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-go, the stop part can last for weeks or even months, the go 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 while the warm blooded animals could remain active.


The Sea

The Antarctic Ocean is cold but the temperature is very stable varying between -2C and +2C over the year. It can go down to nearly -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 aquatic animals to simply slow down to a state of near torpidity (or "suspended animation").

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 they virtually stop - however warm the Antarctic species up and they soon start 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. They also provide a tiny cushion for the end of sharp ice crystals so they are less likely to puncture cell membranes.

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.


Words
endotherm, 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 often very precise, 37C in humans for example, slightly more or less can cause major problems.

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.

Ectotherm - Animals that cannot generate enough energy from internal metabolic processes to maintain a stable body temperature, heat comes from outside of the animal.

Poikiliotherm - 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.

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