How do birds survive a polar vortex?
The winter of 2019 has delivered extreme weather to the Midwest of the United States. Temperatures have plummeted to record lows and much of the landscape is now hidden under a deep covering of snow. Can birds survive the extreme conditions that have already killed several people?
What is a polar vortex?
The cold weather being experienced by the Midwest is the result of a polar vortex. This is an arctic weather system featuring bands of strong winds high up in the atmosphere. These keep the region bitterly cold. Sometimes, the vortex can distort, breaking free from the Arctic. It moves further south than usual, causing havoc in America. It has been colder in Chicago than within the Arctic Circle during the latest bulge in the polar vortex. It is thought that climate change is causing the polar vortex to bulge more often.
The streets are strangely quiet in the big cities with blizzard conditions forcing people to stay indoors. But the birds don’t enjoy such luxury. They have disappeared from the skies and have taken cover to ride out the storm.
Many species of bird are actually surprisingly resilient and can cope with temperatures that see us turning the heating up a few notches. The birds have evolved to cope with the cold and are able to withstand freezing temperatures for much longer than we can. Nature has seen to it that their legs are structured to help them. They boast counter-current blood circulation which means that heat can be transferred to cool veins to prevent the legs from freezing. How clever is that?
How birds prepare for winter
Birds’ legs don’t feature muscles or nerves which also helps them to withstand the cold. They keep warm by fluffing up their feathers to enhance the insulation around their bodies. They may stand on one leg to conserve heat or tuck their feet into their feathers. Some species group together in winter to keep warm.
But birds’ greatest weapon against the cold is perfect preparation. They eat more as winter approaches to consume as many calories as possible and then avoid activity in extreme weather, so they don’t burn off calories too quickly.
Some species also store food in crevices which they can call on quickly without having to move too far if it gets very cold. Insect eating species may peck the ground around them to find food rather than venturing further afield in severe weather. Sadly, birds which have been unable to prepare by eating more food can run into trouble when a blizzard strikes. If their bodies cannot generate enough heat, they will eventually suffer from hypothermia and die.
The importance of good timing
Timing is all for many birds. Those that travel for the winter must arrive at the right time to feed. If the birds arrive too early, there will be no food but if they arrive too late, they miss the flock and are more vulnerable to predators.
Deaths are surprisingly uncommon as the weather is rarely extremely cold for long enough to trouble birds. As soon as the temperatures rise, they get busy eating again, preparing for the next cold snap.