10 Amazing Ways Animals Have Adapted to Survive Below Freeze
When their fingers throb and their speech stutters as they are overcome with shivers, people may wonder why they almost never see animals suffering in the same way in winter. It's true that many animals do better than humans in freezing temperatures, but it's not just insulation and hibernation.
In fact, nature has created many solutions to this problem. Some species have their own way of preparing for a cold period. Others sleep through it and deal with the challenges it brings, while some have no choice but to embrace the cold as they live in it every day. Here are ten of the extraordinary ways animals have adapted to freezing temperatures.
Related: 10 Strange Ways Insects Evolved to Survive
10 Reindeer: ultraviolet vision and eating during sleep
When not helping Santa, the reindeer roam areas where winters are snowy and dark. As herbivores, this is not ideal. They are faced with digging through the snow to find vegetation that is not frozen, and it becomes even more difficult when they want to find their favorite snack. Lichens, a composite of algae and fungi, are a mainstay of the reindeer diet, but they are also white. However, scientists have discovered that reindeer have an adaptation that makes it easier for them to see lichens and predators such as white wolves in the snow: their eyes detect ultraviolet light.
Snow reflects UV light, while lichens and wolves absorb it, making them easily distinguishable from the snow and a reindeer. Still, it's best to be prepared in advance, and they have a nice trick for that too. To help them eat enough and get fat in the summer months when vegetation is plentiful, they can sleep while they chew.[1]
9 Bears: recycle urine
Bears are mammals just like humans. But unlike humans, they can go without moving a muscle for up to five months without their bones and muscle mass completely degenerating. In fact, they can even emerge from hibernation with an increase in lean body mass, despite not exercising, eating or drinking at all during that time. And unlike other mammals that hibernate, such as squirrels, a bear's body temperature hardly drops during this period. This means they burn up to 4,000 calories per day. How can this be possible?
Well, it comes down to something else they don't do during hibernation: urination. Waste products from bone breakdown and proteins, which would normally be eliminated through the urine, are instead recycled while the bears are hibernating. So it is not the case that their bones do not break down if they do not move for a long time, but the waste products released during the breakdown are used to create new bone.
Another waste product, urea, comes from proteins and can cause kidney failure if too much builds up. But bears show no build-up of urea during hibernation, suggesting that this too is recycled.[2]
8 Snakes: Brumation
Typically thought to live in hot deserts or deep in rainforests and jungles, it may be surprising to learn that some snakes also experience harsh winters. In fact, cold temperatures pose a real danger to them because of their already cold blood. Being cold-blooded means that a snake's body temperature rises and falls depending on the external environment. So if conditions outside are freezing, there is a real risk that the hose will also freeze.
To survive cold and snowy seasons, snakes find a cozy place to lie low until it's all over, kind of like many mammals, but with a few differences. What snakes do is called hibernation, and it differs from hibernation in that they don't eat leading up to it. This is because snakes cannot digest food during hibernation as their metabolism becomes extremely slow. Another difference is that some snakes emerge from hibernation on warmer winter days to spend time in the sun and increase their temperature.[3]
7 Fish: natural antifreeze
Deep in the Southern Ocean, the water temperature is barely above freezing, and there are no cozy, dry places to take refuge. For most fish this would be a death sentence as they are cold blooded and would simply freeze. Yet fish, such as notothenioids, survive and thrive in Antarctica. They can live in the coldest seawater in the world because they have a unique internal antifreeze that prevents the formation of dangerous ice crystals in their blood.
When an ice crystal begins to form, it quickly becomes surrounded by a special protein that binds to the microscopic crystal and prevents more water molecules from binding to it and becoming ice. The crystal, now rendered harmless, is taken to the spleen of the fish. To overwhelm the antifreeze and freeze the fish, the water temperature would need to drop to 27.1°F (-2.7°C). But the freezing point of seawater itself is -1.9°C (28.6°F), so notothenioids are completely safe.[4]
6 Wood frogs: freeze but survive
Most animals have adapted to avoid freezing, but the wood frog has adapted amazingly well to freeze and survive. They live on the floor of North American forests up to the Arctic Circle. Although they take shelter under the leaves before winter, they have little to fear when temperatures drop below freezing. When ice gets into their isolated shelters, they crouch, tuck their fingers under their bodies and lower their heads.
When the ice then reaches them, up to 70% of the water in their bodies freezes and they no longer move, breathe, pump blood or show any sign of brain activity. To all outward appearance they are dead. The process involves storing urine in their blood before winter. When the cold sets in, the ice begins to suck water from the frog's cells. To stop this, the frog's liver begins to produce glucose, which binds with the urine and forms antifreeze. This keeps all the water from leaking out of the body, which would mean death.
Amazingly, they can stay that way for months and return to normal when temperatures rise again and they thaw. This strategy ensures that they wake up earlier than other animals that spend the winter underground, giving them time to reproduce safely.[5]
5 Antarctic mosquitoes: rapid cold hardening
Despite being one of the harshest environments in the world, Antarctica actually has some endemic land species. The largest is the Antarctic mosquito, an interesting insect species that proves that fish are not the only animals that can survive the Antarctic cold and that frogs are not the only ones that can freeze solid and stay alive.
These tiny creatures are less than an inch long, cannot fly and spend about three-quarters of the year frozen. They live underground, where the temperature is below zero, but much warmer than the air above. However, their larvae can survive temperatures as low as -15°C.
Scientists have discovered that the survival of Antarctic mosquitoes is due to a mysterious process called “rapid cold hardening.” This prevents injuries while the insects freeze, allowing them to get better quickly afterwards. It is thought that studying this process could also benefit humans. For example, it could improve the way organs are preserved before transplants.[6]
4 Snow flying: self-amputation
Another small insect that can survive freezing temperatures against the odds is the snowfly. But unlike Antarctic mosquitoes, they do not spend the winter in a coma-like state. In fact, they do the opposite: they set out to find a mate and reproduce. This is a major survival advantage for the species as a whole, as they can reproduce when no predators are around.
Scientists have discovered that to make the most of this opportunity, snowflies will keep moving and look for a mate until they freeze to death. Even more impressive, they buy themselves more time to find someone by sacrificing their own limbs when they feel themselves starting to freeze. These traits allow the species to survive above ground in mountainous regions of North America, such as the Cascades, even when temperatures drop below 0°C.[7]
3 Bacteria: transport cells and cold-active enzymes
There are species even smaller than insects that can survive freezing temperatures, possibly for hundreds of thousands of years or more. These are special types of bacteria called psychrophiles, from the Greek for 'cold-loving'. They are specially adapted to survive where no other species can: in the ice, or at least in the tiny veins that form in sea ice and glaciers.
Psychrophiles can undergo different adaptations depending on whether they live in salt or fresh water, but there are a few traits they have in common. One of these is having more transporters on the surface of their cells to speed up the transport of nutrients. This is essential because cold temperatures slow this down. Like Antarctic fish, some bacteria also have antifreeze proteins, and all have cold-active enzymes. These differ from the enzymes found in normal bacteria because the optimal temperature range in which they work is below 20°C.[8]
2 Himalayan songbirds: thick feathers and height limits
Humans are no stranger to using feathers for warmth, so it will come as no surprise to hear that feathers also help some bird species in colder climates stay warm, such as the Himalayan songbird. What's surprising about Himalayan songbirds is that the thickness of their feathers and their color are specifically adapted not only to the mountain range where they live, but also to the altitude at which they live.
Crimson sunbirds live around the base of a mountain in the Himalayas. These usually inhabit areas that are less than 487.7 meters in elevation. Between 5,000 and 10,000 feet (1,524-3,048 meters) are their relatives, the green-tailed honeybirds, and from 11,000 to 13,000 feet (3,353-3,962 meters) are fire-tailed honeybirds. Scientists have recently begun to understand how different birds maintain their altitude ranges.
One factor is the thickness of their feathers, which increases in species that live higher up. Birds shiver to stay warm, but this costs energy. Without sufficient insulation in their feathers, the birds can burn so many calories that they starve. Over time, they have learned to avoid this by sticking to the range for which they are adapted.[9]
1 Ducks: countercurrent heat exchange
Even on a cold, snowy day you can see ducks swimming around in ponds. When the water temperature is close to freezing, the question arises why ducks' feet do not freeze. The answer lies in the way blood is transported through the bodies of ducks and other waterfowl. Their arteries, which carry warm blood from their heart to their feet, surround the veins that carry cool blood back to their heart.
This cleverly warms the cool blood as it re-enters the duck's upper body on its way to the heart. When heat is transferred from the arteries to the veins, the blood flowing in the duck's feet cools significantly. The temperature in their feet can drop as low as 33.8 °F (1 °C), while their bodies are 77 °F (25 °C). This is very efficient and means they lose little heat through their feet in the water because the temperature is virtually the same.[10]