the
mallard
Did you know that mallards exist in every country on the planet apart from Antarctica? Their name derived from the Old French 'malar't or 'mallart' meaning ‘wild drake’, these heavy ducks and bodies are a common sight at ponds, either pecking at pondweed or rushing towards the sound of bread falling into the water. But despite their relatively plain and simple appearance, there is a lot more to this bird than meets the eye...
Mallards can swim in water below freezing and seem unperturbed, and swimmers across the world have envied them after clambering out of lakes or streams and diving for the nearest heat source. Amazingly, the reason for this is because they have a countercurrent heat exchange system between the arteries and veins in their legs – their veins and arteries intertwine (see image left). The arterial blood warms up the venous blood, dropping in temperature as it does so. This means that the blood that flows through the feet is relatively cool – meaning that there is less heat difference between the water around their feet, and their feet themselves. To understand this, imagine getting into a bath that was exactly your blood temperature. You wouldn’t feel any temperature difference, no matter how cold or hot you and the water were. We only feel cold or hot because of heat difference. This ingenious countercurrent heat exchange system means that there is hardly any temperature difference between the feet and the water! It keeps the feet supplied with just enough blood to provide tissues with food and oxygen, and just warm enough to avoid frostbite. But by limiting the temperature difference between the feet and the ice, heat loss is greatly reduced. Scientists who measured it calculated that Mallards lost only about 5% of their body heat through their feet at 0o C!
mallards and water