Many parts of the world have eperienced record high temperatures. In the U.S., 92 all-time record high temperatures had been set through July 16, 2002, according to the US National Oceanic and Atmospheric Administration. Globally, 188 all-time heat records were broken. At least 1,000 people have died from heat-related illness in Portugal and Spain as temperatures climbed to more than 114 degrees F during a heat wave. In the US, more than 40 million people were under heat warnings and advisories on from North Dakota to Texas.
How do birds survive this? Birds have no sweat glands so they can’t perspire to lose heat as humans do. Water evaporated from the skin takes some heat with it but birds don’t carry much water in order to minimize body weight for flight. Only a few flightless birds have urinary bladders; birds use very little water to excrete their wastes in the form of insoluble uric acid. Instead of perspiring, birds lose heat through their respiratory system, consisting of lungs and a system of air sacs attached to the lungs.
Both birds and mammals are homeothermic (warm blooded) and thermoregulate (maintain their body temperature) to keep their bodies from getting too warm and heat stressed or too cold and getting hypothermic. The respiratory system of birds is very efficient and in addition to exchanging gases, the lungs and air sacs expel heat. Some water is lost from the lungs with their complex vascular system, but little from the air sacs. When the birds get heat stressed, they begin to pant, increasing their respiratory rate to expel heat faster. In the case of some birds such as pelicans, cormorants, and other non-passerines, the throat membranes is vibrated, what is called gular flutter.
Behaviorally, there are other things birds can do to cool off. Some fluff their feathers or spread their wings to expose more skin to the air. Some seek shade under brush or trees or even burrows. Some long-legged birds defecate on their legs, the small amount of moisture evaporating to provide a bit of cooling.
Desert birds, of course, face the greatest risk of overheating. They are adapted to the higher temperatures with, for example, smaller body sizes and lighter plumage. In the Naroo Shrubland of South Africa, researchers studied 12 species of birds in two groups: drinkers and non-drinkers. The drinkers flew to water holes to drink while the non-drinkers obtained their water from juicy insects. The drinkers, as a result, imbibed more water and were able to cool themselves more readily and withstand temperatures a bit higher.
What can we do? Put out bird baths or other water supplies for our feathered friends. They especially love dripping or slow flowing water. If you are in a drought area, a drip line with water dripping at one or two drops per second seems to attract songbirds more than standing water (and put the container among plants that require watering). The water container should be shallow as well so birds can bathe. Luckily, in the northern hemisphere, fall is approaching.