I was talking to a fellow birder the other day about how we were both noticing that it seems to be getting hotter earlier in the year and this got us talking about how we stay cool when we get hot. We started talking about birds and how they cool down when hot, which led us to ask whether birds sweat.
Birds do not have sweat glands and so do not sweat. Birds cool down using water, shade, breeze, cool air, panting, and in some cases, defecating on their legs. Birds can overheat quickly and by using a combination of these they can regulate their temperature when hot.
Sweat is used to cool the body down and most mammals sweat to evaporate the heat from their bodies, but birds do not sweat. Birds use a lot of energy and can get hot very quickly when flying but they need to use other methods to cool down.
Why don’t birds sweat?
Birds do not have sweat glands so they cannot sweat as mammals do. However, even if they did have sweat glands this would still be problematic for them.
Because birds are covered with feathers, sweating would be a major problem. Feathers are used to insulate the body so this would stop the moisture from evaporating from the skin. This could cause birds problems with bacteria or fungus growing.
While oils on the top of feathers make most birds waterproof, the feathers underneath can get wet, especially if the moisture is coming from the skin. This would lead to the feathers getting wet, causing them problems if they tried to fly.
Do any birds sweat?
While no birds possess sweat glands, some birds that feed on nectar such as hummingbirds and sunbirds do need to get rid of the extra water they consume.
Hummingbirds beat their wings between 50-80 times a second, and the heat in their bodies can build up very fast. Because of their diet and rapid movements, hummingbirds, sunbirds, and sugarbirds use evaporation to remove the excess liquid. The evaporation assists water loss from the kidneys and digestive tract.
Water is also lost through the skin as part of natural dehydration in some species.
How do birds regulate their temperature?
Birds need to regulate their temperature throughout the year, and the warmer seasons are no different. Birds generate their body heat through the nutrients they consume, with an average body temperature of around 40 degrees centigrade.
The body temperature varies per species, with passerines usually a couple of degrees warmer. Nocturnal species are generally warmer at night, while diurnal species usually are warmer during the day.
Birds need to maintain a stable temperature, and to do this, their heat production and heat loss need to remain balanced.
Small birds are more prone to heat loss than larger species as their surface area is large relative to their body mass.
How do birds cool down?
Because the outside temperature affects birds, higher temperatures mean that the birds need to insulate their bodies less than when it is cold.
When hot, birds will ideally drink more water to cool them down. When hydrated, birds can use water for evaporative cooling. Birds that live on the water will never be as hot as birds that don’t, but most birds will stand in the water to cool down or splash about. Standing in water helps cool the scaly skin down.
Species such as kingfishers and bee-eaters can be seen diving into the water to cool down, while swallows will swoop over the water to get their chests wet.
To control their internal temperature when it is hot, birds have several ways to cool down. Birds that are too hot can often be seen spreading their wings to let areas underneath breathe. Feathers are often sleeked back, and more of the bird’s bare areas can be seen.
Many birds will face away from the wind and ruffle their feathers, allowing the cool breeze to get to their skin. An insulating layer of air is trapped around the body by fluffing the plumage. This slows down the heat transfer from the environment and allows the breeze to cool the skin.
Birds can often be seen panting, similar to how a dog does. Evaporation occurs through the respiratory tract, and moisture is expelled into the air. Non-passerine birds, such as parrots, owls, and falcons, use a cooling mechanism known as gular fluttering, where they move the mouth, and the throat rapidly moves up and down.
This increases the speed of the air moving through the gular sac. The air is moved rapidly, and this causes heat in the blood vessels close to the surface to dissipate. Evaporative heat loss happens at the same time through moist membranes. Gular fluttering also helps get cool air into the body.
Seeking shade is one of the most common ways birds keep cool in hot climates. Finding shade under a tree can reduce the body temperature considerably.
Tropical birds often have lower metabolic rates than non-tropical birds, while some can lower their metabolic rate when the temperature rises.
Birds of prey will often take to the skies to find cooler pockets of air, and many birds can be seen higher up in trees than on cold days to benefit from the cooler breeze.
Some birds go to more desperate measures to reduce their temperature. Storks, turkey vultures, and gannets can often be seen defecating on their legs to cool them down, a process called urohidrosis. This assists with evaporative cooling and reflects solar heat as the waste is usually white.
Ground birds can often be seen standing as tall as possible. By exposing less of their bodies to the ground, birds can cool themselves down. By keeping their bodies away from the warm ground, birds can lower their temperature.