Birds handle heat better than mammals

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Oh, to be a bird now that August is here. I confess I am miserable in the heat of summer. When the thermometer tops 100 degrees everything outside is a chore. The wall of heat greets me as I step from the house to weed or to mow or even to head for the car to run a few errands.

A doe suffers the heat in the shade, annoyed by the ever-present flies adding insult to injury. At least I can retreat to a cooler house. To be a bird is to be spared much of this grief.

Jays, orioles and black-headed grosbeaks worry the fruit on the flowering plum trees without pause. Swallows and red-tailed hawks endlessly cruise the skies. Even the family of chickadees continues its spirited search for insects in the heat of the afternoon. The heat doesn't affect them as it does us poor mammals.

The secret lies in their body temperature. Humans run at a cool 98.6 degrees farenheit, while most small birds operate at a feverish 105.1 F. Birds play a dangerous game by operating at such high temperatures. Humans with a fever this high risk serious harm. A great many proteins are damaged irreparably at temperatures just a touch higher than this. A bird that runs a fever is in real trouble. Even at a normal 105.1 F there is a high turnover in proteins. The damaged molecules must be replaced, putting nutritional demands upon birds much greater than for cool-running mammals.

Despite the risks, there are rewards that I envy — especially in August. If you or I sit quietly in the shade at temperatures of 98 or lower, your body will continue to lose heat to the environment without you doing a thing. If you step into the sun or actively work or play, you build up heat faster than you can passively lose it to the air. This is where sweating comes in. Evaporating sweat cools the body.

Birds, on the other hand, don't have to worry about heat build-up until the temperature reaches 105.1 degrees. Of course if they sit in the sun or actively work, they have the same issues that you or I would. Still, they have more than a 6-degree margin of comfort over us. In August, I'd take it, given the choice.

This is a good thing for birds, because sweating is not an option. Sweat mats feathers and destroys the ability to insulate. It's not a surprise that birds have no sweat glands in their skin.

About the only recourse a bird has when it gets really hot is to pant. Moisture evaporates from the inside of the mouth and throat, providing some relief. This panting in birds is called gular fluttering. In larger birds you can see the skin of the throat vibrate. This moves the air about, increasing the rate of evaporation. A dip in a bird bath also helps.

I really shouldn't complain about the heat. As I contemplate my lot in life as a mammal with an "engine" that tends to overheat, I am sitting inside an air-conditioned house with iced tea in hand. It's really not so bad, and fall is quickly approaching.

Stewart Janes is a Biology Professor at Southern Oregon University. He can be reached at janes@sou.edu.

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