If you have ever wondered how the mallards on Lanark Loch manage to stand on the frozen water over winter for hours on end without the hint of discomfort then you will be amazed by what I am about to tell you! Many birds have a counter-current heat exchange system at the top of their legs. It sounds rather complicated but it is an ingenious adaptation that allows birds to avoid losing heat through their scaly feet. Human beings in comparison are rather Neanderthal-like losing heat as if the sun shone down upon us every day! In humans and many other mammals the arteries and veins in the legs are quite far apart. In many birds these arteries and veins branch around one another like a webbed embrace. This means that warm arterial blood going down to the foot transfers across to the venous blood that comes back into the body. In humans warm blood travels all the way down to our extremities and cools as it goes so by the time it travels back up our veins and into our body the blood has dropped in temperature. This is evident when you go paddling in the sea or if you injure your foot and ice it to reduce the swelling; not only do your feet get cold but your whole body starts to cool down as well. With birds, only 5% of heat is lost through their feet because all their heat is transferred across, so in essence the warm blood never really leaves the bird’s core. Therefore birds can stand on the ice for hours without getting cold and to prevent their feet from freezing every once in a while warm blood is allowed to travel down to their feet.
Next week: Find out about our Upper Nethan Gorge tree-planting event!
Laura Whitfield – Falls of Clyde Ranger