Why Do Birds Have A Core Body Temperature Higher Than Other Animals?

There are several proposed reasons for why birds have a higher core temperature than mammals. First, birds tend to have more metabolic needs than mammals. Flying and incubating eggs are energetically costly and raise the core body temperature of birds. Feathers provide further insulation that keep birds warm.

As a kid, did you ever want to simply fly above the world? I certainly did! All I wanted was to morph into a colorful little bird, ruffle my feathers, and spread my wings. But flying isn’t that easy. A lot goes into making those tiny bodies glide through the skies, braving all sorts of weather.

One by-product of being able to fly is body heat. If you ever hold a bird in your hands, you will instantly feel its warmth, because they have a core body temperature significantly higher than ours.

Wonder why?

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How Do Different Animals Produce Heat?

Since we’re talking about why birds are hotter than you, me, and your pet fish or dog, we must look at the rest of the animal world and identify how they produce heat. Your body temperature, or that of any animal, depends on a few factors: whether we produce our heat, body mass (how large and heavy the animal is), and the energy needs of the animal (a cheetah has very different needs from a sloth, which has very different needs from a frog).

In terms of how different animals produce heat, we can broadly divide them into two groups—ectotherms and endotherms.

Ectotherms are animals whose body temperatures depend on the temperature of their surroundings; they do not generate any heat themselves. Their external environment helps regulate their body temperature. For example, a snake bask in the sun to raise its internal temperature. It later retreats to its burrow to cool down. Likewise, frogs sit on the rocks to warm themselves and return to the water when it needs to cool down.

These ectotherms are also known as ‘cold-blooded’ animals. They include fish, amphibians, and reptiles.

Endotherms, on the other hand, can regulate their body temperature by generating internal heat. Regardless of the ups and downs of the environment, they can maintain their physiological body temperature within a stable range. In the cool winters, they ramp up their metabolic heat production and insulation to stay warm, whereas during the hot sweltering summers, they sweat to cool down.

Thus, all their metabolic processes occur at a constant temperature.

Endotherms are also known as ‘warm-blooded’ animals, and include mammals and birds.

Also Read: What Is An Ectotherm?

Metabolic Needs Of Birds

So, mammals and birds are both endotherms, so why do birds need more energy than so many other mammals? On average, a bird’s body temperature is approximately 4 to 8 degrees higher than that of humans.

A few probable reasons are available.

While a mammal’s fur only helps in insulation, a bird’s feathers have a dual function; they allow the birds to fly and keep them warm.

Flying at high altitudes makes them more susceptible to unfavorable conditions, such as cold weather and freezing winds, which can chill them to the bone. Additionally, their wings allow them to fly, and flying requires the muscles to work harder and use more energy.

Insulation from the feathers and the heat from hard-working muscles lead to a higher internal body temperature.

Even then, mammals can sweat to cool down, but birds do not have sweat glands. They only lose heat through their exposed skin and respiratory system.

This heat isn’t pointless. Birds generate heat to incubate their eggs. They sit on their eggs to help them stay warm. This heat is essential for an embryo to develop properly into a chick. Without adequate incubation, eggs would fail to hatch. Mammals do not face this issue, as most of them directly give birth to their young ones.

At a very basic level, birds engage in more energy-costly activities as compared to mammals, and they are smaller.

Size

Correlating body size and body mass with core body temperature is tricky. A study published in 2007 found that there is a relationship between size and core body temperature among birds. Their study compared body temperatures and size of birds phylogenetically (in other words, according to the evolution of birds). Smaller birds such as the passerines (birds that perch) as a group have a higher core body temperature than non-passerine birds. Large birds such as the ostrich and the moa (and others in the group ratite) have a body temperature closer to mammals.

None of this discussion has considered the environment and time of the day. Some bird, such as the hummingbird, can lower their body temperature at night to conserve energy. They lower their body temperature by 3 degrees! If your body temperature tanked by 3 degrees, you’d be in the hospital for hypothermia.

Also Read: What Is An Endotherm?

To Sum It Up…

Birds are endotherms or ‘warm-blooded’ creatures who regulate their body temperature. On average, birds are involved in highly demanding activities with a lot of energy expenditure, including flying and incubating eggs. Without the production of adequate heat, birds would not be able to survive the cold temperatures greeting them at the heights they fly.

Moreover, their eggs will not hatch if there is inadequate heat during incubation. Therefore, their energy requirements and expenditure is way higher than other creatures of the animal kingdom. This results in higher metabolic activity and a consequently higher core body temperature.