How do fish and water birds cope with winter?

Storks fly to warmer countries, bears retreat to their cozy dens, and lynxes grow thick fur. But it’s hard not to shiver at the thought of animals forced to spend winter in icy, often frozen water. Fortunately, nature has equipped fish and waterfowl with fascinating adaptive mechanisms.

Fish in winter – in blissful lethargy

Fish are cold-blooded animals, meaning they cannot maintain a constant body temperature. As the surrounding water cools, so do they. However, instead of developing hypothermia, they gradually slow down their metabolism in response to the cold: movements, heart rate, and respiration decelerate to conserve energy.

When rivers, ponds, and lakes freeze over, fish paradoxically thrive. The ice layer acts as insulation, and near the bottom, where water density is highest, the temperature remains steady at around +4°C. Since ice allows sunlight to penetrate, algae in the water can continue photosynthesis, producing oxygen for the fish. Winter may not be an exciting time of year for fish, but it allows them to peacefully await spring, no matter how harsh the frosts or blizzards on land.

Interestingly, some species of fish living around Antarctica have a special protein in their blood that acts like… antifreeze.

Water birds – warm coats, cool feet

Birds, despite being warm-blooded, have also adapted their metabolism to harsh weather conditions. During severe frosts, they sit passively on the water, avoiding unnecessary exertion. The key to their comfort lies in their winter plumage, which can be compared to Gore-Tex. Close to the skin, they have short, fluffy feathers that create air pockets and provide excellent insulation against the cold. No wonder the best winter jackets are still made with goose down!

Additionally, the outer layer of feathers features micro-hooks that interlock, forming a waterproof cloak. To stay dry, ducks also produce a special oil from glands near their tails, which they spread over their feathers by preening. This oily layer protects the skin from cold water, much like petroleum jelly.

But that’s not all! Ducks, geese, gulls, and other water birds have developed a fascinating mechanism called countercurrent heat exchange. This process limits blood flow in such a way that cold blood from the legs doesn’t circulate through the entire body but is instead warmed locally by arteries located close to veins. Their feet remain cold but are protected from frostbite, and the overall body retains its precious warmth.

When winter becomes exceptionally harsh, swans tend to move to land, curling up with their legs tucked under their feathered bellies and heads nestled under their wings. This minimizes heat loss. Interestingly, standing on one leg, with the other tucked into their feathers, also helps conserve warmth.

How can you help?

It’s common for people to see ducks on a frozen pond and think, “Poor things,” before heading home to grab a bag of stale bread. Later, bundled in warm hats and coats, they proudly watch the birds squabble over crumbs. Unfortunately, this isn’t the best way to help.

Scientists from the Wrocław University of Environmental and Life Sciences confirm that feeding water birds in winter is beneficial, as extra calories help them cope with the cold when natural food sources are scarce. However, birds should not be fed bread, salty or sweet pastries, pretzels, or chips. This diet, rich in salt and bread acids, disrupts their water balance and digestive systems, which can tragically lead to death.

If you want to help birds during winter, bring what they truly need: grains or raw vegetables. It’s best to scatter food on the shore, as it spoils too quickly in water. And never feed birds directly from your hand – taming wild animals is one of the worst things you can do to them!