AVIAN COPING MECHANISMS FOR HEAT AND DROUGHT
By Jon Friedman
July is a particularly challenging month here in Southern Arizona. We've been in a long, sustained drought for over a decade. It's going to take an amazingly wet monsoon season (or two or three) before scientists declare a temporary end to this drought. Historical records and ever advancing climate change indicate the possibility of many more years of drought to come. And, dry as it has been, we've seen soaring heat as well. We've experienced record setting or near record heat this year and the past several years. The snowbirds, i.e. winter resident birds and humans, have already flown to cooler climates. We watch as the prickly pear cactus pads shrivel, riverbed mud dries into cracked irregular tiles and wildlife retreats into whatever deep shade they can find. Only the toughened desert dwellers remain - desert rodents, lizards, snakes, spiders, scorpions and centipedes, ground squirrels, foxes, coyotes and desert tortoises find burrows and underground dens to escape the hottest parts of the day. It's rather amazing then to consider the large numbers of birds that brave the summer's dry heat.
In our famed dry heat, all living plants and animals adapt to extreme conditions. We humans find shade, and air conditioning or cooling in the modern comfort of our homes. When thirsty, we pour ourselves a cool drink with relative ease. We hardly think twice about it. Given that we exercise some of our taunted high intelligence and don't run our wells or the Colorado River dry watering our golf courses, pools, yards, gardens, agribusiness, and our ever growing population, we can keep our need for water well satisfied, for the time being at least. However, not all the animals and birds that live in the desert find water as easily.
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Cooper's Hawk by Richard |
As the summer comes on, you may notice birds in your yard seeking shade, and perching with mouths wide open and wings held folded but away from their bodies. When we see this happening, we know that these valiant little birds are heat stressed. We check to see that our birdbaths have water in them, and that the drippers, misters and wigglers placed around/ in the baths and vegetation in the yard are turned on and working well.
Nature has provided birds with mechanisms for keeping cool, as she has done for humans. We humans have sweat glands in nearly all the areas of our skin. Our sweat glands respond to increased exercise, environmental temperature or fever by releasing fluid onto the surface of our skin. As the sweat evaporates, it carries heat away from our bodies. Birds can't sweat! They have no sweat glands. So, what else has nature done to assist our feathered friends when summertime temperatures soar?
A bird uses its respiratory (breathing) system to combat high temperatures. This system is the most efficient known among all animals with backbones (vertebrates). When a bird breathes in, air passes through its nostrils into the mouth, pharynx and through its glottis, a slit-like opening that is surrounded by the larynx. The larynx in humans contains our vocal cords, but in birds it does not. It is a simple valve that opens and closes the glottis during breathing. This prevents the birds from swallowing food down into their lungs. The inhaled air passes through the glottis, then down through the windpipe (trachea) and then through the birds voice box or syrinx. From the syrinx, the air travels through the paired bronchi into the lungs. From the lungs, it passes to a series of air sacs that are peculiar to birds. Some lizards, snakes and some larger active insects also have air sacs. Air sacs are like large, thin-walled soap bubbles that extend from a bird's lungs to different parts of its body. The number and exact placement of these air sacs varies from species to species.
Air sacs play no direct role in the exchange of oxygen and carbon dioxide; instead they contribute to the comfort and functioning of a bird by providing extra air circulation to help dissipate the extra heat generated by a flying bird. The air sacs have branches (diverticula) in nearly every part of the skeleton of many birds. Such pneumatized bones suggest that there is a relation between flight and light-weight bones. Air sacs also contribute to the buoyancy of some water birds, and seem to cushion the impact of gannets and Brown pelicans when they crash into the water while fishing.
Warm, moist air is collected from overheated tissues and expelled through the lungs. Fresh air is brought into the body and picks up heat radiated from body cells and blood. Exhalation removes excess heat. When the ambient temperature reaches 105 degrees and over, a bird's breathing rate increases. It begins to pant, which makes more air flow over its moist mouth, pharynx, bronchi and possibly even its air sacs. All this helps to cool it down, and is essential to its survival. According to some researchers, this cooling process is much more important to birds than the taking in of oxygen.
While panting cools down the birds, it has its price. Moisture is removed along with the heat. To prevent dehydration, most birds must drink water. Small birds lose more water from panting than larger ones. An external source of water becomes critical for them in our hot, dry summers. Some birds can survive by eating succulents and insects (which have high moisture content), but many will die without clean, available, reliable water sources that we can easily provide for them. Thirsty birds that cannot find water often die after drinking pools of engine coolant (anti-freeze) they have discovered on or along our roads or in parking lots. Several condors in hot Southern California were featured in the news when this became known. Studies of birds in deserts worldwide have shown that, even without sweat glands, extreme temperatures can exceed a bird's ability to cool and lead to deadly dehydration.
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Images by Richard at SearchNetMedia
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Panting is not the only way birds can cool off. Some desert-adapted species, like the Australian Budgerigars and Zebra finches and one of the Sonoran desert's most common and best singing songbirds - the Black-throated sparrow reduce their water losses by lowering their metabolic rates. They can survive for long periods of time on a diet of dry seeds alone. However, these birds are in the vast minority of birds. Many birds must fly long distances for life-sustaining water. Owls, Gambel's quail, Great blue herons, nighthawks, poorwills, roadrunners, doves and pigeons flutter the skin of their throats (gular fluttering) to cool down. Brown towhees and Black-throated sparrows use abandoned burrows to escape the summer heat. When the temperature is over 95 degrees, many birds become much less active, and find shady (and hopefully moist) places to pant and rest. Providing a fresh water source such as a birdbath can be a life-saver for many of our desert birds in our summer heat.
Ornithologist D.E. Hatch subjected five Turkey Vultures to rapidly rising temperatures. Before they even began to pant, he found they employed another method of cooling. They deliberately defecated on their legs. This caused their body temperature to decrease by 1 degree centigrade, a feat that panting could not produce. Cormorants and Turkey Vultures use yet another means of thermoregulation when the heat comes on - they spread their large wings, much like they do when they are drying them off. In the Sudan, large birds like ravens, Hooded vultures and Black kites cool themselves by rising on warm columns of air to over 3000 feet above ground level where the air is considerably cooler.
Why not help our birds, especially during these particularly hot summer months, with clean, dependable and safe sources of water? Our website is full of practical, functional, affordable items that you can consider for this purpose. Prices on the website are the same as in the store. Or, pay a visit to our new location and any of our friendly knowledgeable staff will glad to assist you and answer any questions you may have. If you haven't visited our new and expanded store, this is your invitation to do so. See you soon and enjoy the birds!