Birds are warm-blooded and can regulate their temperature, but they need to keep warm and avoid hypothermia to survive harsh winters. They have many different ways of doing this, and in this article, we look at some of the ways that they keep warm.
Birds use the sun to warm their bodies without using any energy. Huddling together in groups can save a lot of energy, as can roosting in warm nests. Birds will trap air in their plumage to keep themselves insulated, but birds will increase their metabolic rate to shiver and warm up if none of these methods works.
Birds can use a lot of energy to keep warm, and they need to eat plenty of food to regulate their temperature. However, there are other ways for them to stay warm. If you want to know more, please read on.
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Why do birds need to keep warm?
Birds use various methods to regulate their temperature and keep warm, ranging from physiological mechanisms to simply sitting in the sun.
Birds are warm-blooded and can regulate their temperature. Keeping warm is very important for their survival, and they need to keep their body temperature steady so that they are not at risk of hypothermia.
Birds are homeothermic and keep their body temperature between 40 and 42 degrees centigrade. The internal temperature is different depending on the bird’s size, which affects how cold they can get before getting sick. If the bird gets too cold and the body reaches the lower critical temperature, they realise that they need to raise their body temperature.
Small birds heat up and cool down quicker than large birds due to the high body surface area to volume ratio. This means that they reach the lower critical temperature faster than large birds. Large birds can keep their temperature stabilised easier than smaller species. Larger birds have a lower critical temperature as low as 5 degrees, while smaller birds may have an LCT of 30 degrees.
Once the lower critical temperature is reached, the body will shiver to warm up. Birds can triple the metabolic rate, but this comes at an energy cost, and they will need to eat soon after.
If the body does not warm up, the body reaches the lower lethal temperature. The body can’t produce enough heat at this temperature, and the bird will get hypothermia and likely die.
In cold areas, birds are generally larger. This occurs even in the same species, where birds further north are larger than those in the south. Birds in colder areas also have more feathers than those in tropical regions and a thicker plumage.
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How do birds keep warm?
Birds keep warm in different ways, but the easiest way is to use the sun. Birds can often be seen sunning themselves either on the ground or in trees. Doves can often be seen laying flat on the ground with their wings outstretched to warm their upper bodies before lifting one of their wings to let the sun get underneath.
Birds can often be seen high in branches with their wings open, facing the sun to take advantage of its rays. I often see a cormorant on a perch over the water drying itself out with its long wings outstretched after it has been fishing.
Sunning allows birds to reduce their metabolic heat production without using any energy, so it is the most common way for birds to warm up.
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Many birds roost together, and by huddling together, they can share their body heat. They do this on branches or in nests which serves two purposes. This keeps them warm and also helps them stay safe from predators.
By huddling together, each bird saves almost half of the energy it would expend on heat if they were alone. The number of birds huddling together can make a huge difference, with the RSPB stating that two long-tailed tits huddled next to each other can save 27% of their energy, but three increases the saving to 39%.
Birds will often find shelter to help them keep warm, especially when it starts to snow. Birds can be found roosting almost any place that is safe and warm, including houses and barns, but also on top of mechanical structures such as air conditioning units and heaters that are often warmer. Birds can sometimes be seen resting on rocks that have been warmed by the sun.
Because birds do not have feathers on their legs, the legs are often exposed to the elements. Birds have a couple of different ways of keeping their legs warm. They can often be seen pulling them into their bodies, allowing the feathers to warm them up. The legs are pulled up to the belly, and they sit in a hunched position to keep them warm.
The legs also have arteries that carry blood from the heart alongside the veins carrying cold blood from the legs. This warms the blood, keeping the legs warm.
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Birds don’t only hide their legs in their plumage. They can also be seen hiding their faces under the wings or standing on one leg to reduce heat loss and keep warm.
By fluffing their feathers, they can trap air into their plumage. This helps keep them warm as the air is insulated in the feathers, although this only occurs when they are resting.
Birds can nearly double their plumage volume by trapping air, reducing heat loss by more than one-third. In winter, birds in colder areas often have denser plumage than birds in warmer areas, even of the same species.
Many birds, especially smaller species, have to increase their metabolic rate in winter to keep warm. Some will increase their rate by up to 40%. However, this comes at a price as they need to eat more to maintain this higher rate. Food is not always easy to come across in the harshest weather, which can cause problems for smaller birds.
Most birds that live in colder areas are larger non-passerines with dense plumage to keep them warm.