Ask Audubon Do birds perspire? 

Ray Tillmann, Menard, Illinois

Technically, only animals with sweat glands can sweat. Birds lack them, but being warm-blooded, they still must have some way to cool down when it's sweltering outside or they risk meltdown. Short of switching on a fan--which, incidentally, domesticated pigeons can be trained to do--they accomplish this by means of a number of thermoregulating strategies. Primarily, birds off-load excess heat either by evaporative cooling directly through the skin or by panting. The latter method cools the bird's airways and helps lower an elevated internal temperature. A robin running across a lawn on a sunny afternoon with its beak agape is doing exactly that. To supplement panting, several species vibrate the muscles and bones in their throats, a tactic called gular fluttering.

Bathing also beats the heat, as does ruffling feathers, seeking shade, and taking a siesta. Cormorants chill by perching with wings outspread. Other species, like black kites, ascend on thermals to reach higher, colder altitudes. Laysan albatrosses simply lean back to expose their feet to the breeze. Perhaps the most unique heat-dissipating antic belongs to some storks and New World vultures, which deliberately defecate on their legs. When the wind blows--voila!--natural air-conditioning. It's messy, but, hey, it does the trick--no sweat.

Why do June bugs fly around at the same time every evening?

Sandy Briggs, Ontario, New York

For the same reason that teenagers cruise on Saturday nights: romance. During a few fleeting weeks in June and July, swarms of ardent European chafers (which are often mistaken for June bugs) participate in an annual ritual that not only ensures the perpetuation of their species but also spells the end of their brief adult lives. Every evening, the beetles set forth at approximately 8:30, when the sun is slipping below the horizon. "Once the number of lumens reaches a certain level," says Cornell University entomologist Paul Robbins, "these guys come boiling out of the ground, looking for a vertical object to congregate on." And conjugate on. For the next half-hour, the air is abuzz with their beating wings. They convene en masse (sometimes by the thousands) around the chosen trysting place--usually a tree or shrub but occasionally a telephone pole or chimney--then find partners for a dos-si-do that lasts well into the wee hours. Couples start falling from the trees at about 10, and flights back home continue throughout the evening, with stragglers returning at dawn. Each insect has about six days to fulfill its biological imperative, just the amount of time it takes to use up all the fat gained during a yearlong larval feeding blitz. Then it dies. 

Any question about the origin of the expression "Crazy as a June bug"?

The leader of an owling walk told me that the night vision of humans and owls is comparable. True? 

Bonnie Campbell, Kalamazoo, Michigan

Unless you can spot a vole more than a football field away, your night vision is as similar to an owl's as, well, night is to day. Once the sun sets, it's no contest. In truth, no creature can see in total darkness. But owls have a keen sense of sight in dim light, which, coupled with an acute sense of hearing, makes them superb nighttime hunters. The ancient Greeks believed the birds' extraordinary vision emanated from a magical inner light. Superstitions notwithstanding, owls are endowed with ophthalmic assets befitting their lofty position on the food chain. They possess gigantic eyeballs, which can better absorb low-level ambient light (if our eyes were proportionate, they would be as big as grapefruits!). Complementing each super-size orb is a powerful lens, a broad retina, and a pupil capable of dilating to a great diameter to collect photons under even the duskiest conditions. Like other vertebrates, owls have two types of sensory cells in their retinas: light-sensitive rods and color-sensitive cones. Their retinas are densely packed with rods, at the expense of cones. Thus, they can better distinguish small moving objects--albeit, probably in monochrome--while flying beneath the crepuscular canopy of a forest. Some owl species boast nearly a million rods per square millimeter (people have about 200,000 per square millimeter). Furthermore, owl eyes contain a tapetum, a mirror-like membrane that amplifies light and gives rise to eye shine, the phenomenon that causes your car's headlights to reflect off of animals' eyes after dark. The birds' sharp audiovisual system works in concert with silent flight and spatial memory to keep them from being among those creatures that go bump in the night. 

By Carolyn Shea 

© 2000  NASI

Illustrations by Jonathan Carlson

Baffled by Nature?  Ask Audubon!