The tiny legs of birds — like those of the greenfinch — are hardly two millimeters in diameter. How can they flit around in the snow all day, at the most unpleasantly low temperatures, when our thick fingers and toes already start hurting at temperatures just below freezing?

Birds have veins built in the form of heat exchangers. That protects the feet from freezing even when walking on ice. Through a finely arranged mesh of blood vessels called rete tibiotarsale, blood flowing from the body into the feet transfers warmth to the blood flowing back into the body. This way, the blood in the feed is colder, but the body doesn't lose much heat.

Just like in a building, this heat recovery system can be turned off in warmer temperatures. Then the feet fulfill the function of emitting surplus heat, since birds cannot sweat because of their feathers. In winter it's essential for them to find enough food to keep up their body's energy supplies. As long as there's not too much snow, they will find something to eat.

When there is too much snow, humans can help out. Blue tit and robin are devouring their special meal made up of seeds and grains held together by fat. There's a lot of energy in this! Another reason birds don't get too cold: their fluffy feather dress. It protects them just as well as a down jacket does us humans.

His feather dress includes an outer protective shield of coverts and fine down underneath, creating a thick air cushion. The Kingfisher can not only move through air, but even through icy waters. Running streams that do not freeze in winter are his hunting grounds. But finding open water that also holds enough small fish can be difficult for the beautiful bird.

Hedgehogs eat a lot in the fall to — hopefully — build up enough fat reserves before winter. Their best place to hibernate is a big pile of old leaves that will keep the ice out. If snow falls on top of it, even better! That will offer additional insulation. If you find weak or sick hedgehogs in winter, contact your local animal shelter. And before you burn piles of leaves, check for hedgehogs!

The dormouse goes underground in the winter. It will dig up to one meter deep into the soil. During hibernation, he lives off his body fat reserves, which he accumulated over the summer. To use as little energy as possible, the dormouse can reduce its pulse from the usual 300 to five beats per minute. His body temperature drops down to roughly five degrees Celsius.

Mice like to stick close to humans - like living inside a compost heap. Temperatures there usually stay above freezing. Another advantage: There will be enough food to go around. In winter, even carrot peels are better than nothing.

Bats are hibernating in frost-free caves, basements and attics. There they form colonies, keeping each other warm. They reduce their body temperatures so it's just slightly higher than that of their surroundings. Mating takes place in the winter quarters, but the actual fertilization in the body only happens when it gets warm again. By the time the young ones are born, it can be summer again.

Large mammals like deer or wild boar that don't hibernate have to find enough food to survive the winter. That means they have to save energy and should not move too much. Disturbances can be dangerous for them. If you see them on a walk through the forest, stay away and keep your dog out of reach as well.

Those two frogs are sitting on freshly fallen snow — but they won't stay there long. Usually reptiles and amphibians will seek protection in the underwood or little caves and crevices. There they hibernate with very low body temperatures.

Most insects will retreat and hide in tiny holes in wood, hay or in rocky areas. Mosquitos are probably an exception. Their eggs can survive underneath frozen water. Even in the middle of frigid winter, some mosquitos can be found buzzing around. Where there are human settlements, there will always be some puddle of water where the insects can lay their eggs.