The Wild File


Q) How many calories would a hummingbird need to consume in a day if it were the size of a human?
Mark McCubbin, Madison, Wisconsin

A) THE DIMUNITIVE BIRDS John James Audubon described as "glittering fragments of the rainbow" have a faster metabolism than any other vertebrate on earth. The reason, says Robert Dudley, a professor of integrated biology at the University of Texas at Austin who specializes in all things hummingbird, is that unlike most birds, which flap their wings vertically to keep aloft, hummingbirds beat their wings nearly horizontally—roughly 53 times per second—as though they were treading water. This allows them to hover in places like helicopters when, say, feeding on sugar water outside your window. Of course, such hyperactivity takes its toll. An average ruby-throated hummingbird—the common East Coast variety—weighs just four grams but burns around three and a half calories per day. Just to stay alive, says Dudley, it must find thousands of flowers and drink approximately its body weight in nectar each day. Computing the calories required per gram of weight, you'd find that a man-size hummingbird of 180 pounds would need to scrounge up around 82,000 calories every 24 hours—the equivalent of 228 chocolate milkshakes. God save us all from the day when humongous hummingbirds descend on our diners in search of vital carbs. "It wouldn't be pretty," warns Dudley. "It just might get downright ugly."

Q) What is the highest unclimbed mountain in the world?

Philip Rush, Arlington, Virginia

A) IF BY MOUNTAIN you mean individual massif (as opposed to an outcropping that's part of another mountain), 24,829-foot Gangkar Puensum on the border between Bhutan and Tibet currently holds the coveted title. This is according to Joss Lynam of the International Mountaineering and Climbing Federation, which represents some 88 climbing organizations worldwide and keeps tabs on first ascents (or the lack thereof) of the earth's loftiest summits. In 1986, two teams—one British, one Austrian—attempted the summit via the South Ridge, but neither was able to top out. So why hasn't the bastard been knocked off since? Two words: religion and politics. For over ten years, Bhutan's authoritarian Buddhist government has imposed a countrywide ban on mountaineering, claiming that its peaks are sacred. China, meanwhile, has been less than forthcoming with permits to climb from the Tibetan side. In 1998, a Japanese team was granted permission to ascend the peak, but in a textbook example of cryptic Chinese diplomacy, the government "postponed" the permit, citing sensitive border issues. Instead, the climbers got clearance for a successful 1999 bid on 24,711-foot Liankang Kangri, where they were left an agonizing few kilometers away—and just 118 feet below—the highest peak on the same massif, Gangkar Puensum.

Q) Why do hammerhead sharks have such strange-shaped heads?

Eric Waters, North Vancouver, British Columbia

"GOOD QUESTION," says Kim Holland, a professor at The Hawaii Institute of Marine Biology outside Honolulu. "I just had a student earn his Ph.D. on this very subject." For starters, he explains, the wide head acts "like a canard," providing lift and making the shark a more agile swimmer (bad news for the speedy squid, one of its favorite snacks). The hammer-shaped mug also enriches the shark's sensory system. Its two nostrils occupy prime real estate on the front corners of the broad head, where they're spaced far enough apart to detect changes in the concentration of a scent from one side to the other. This makes the shark an olfactory all-star, able to narrow in on its prey. But perhaps the most important function of the odd-shaped noggin, says Holland, is the added surface area it provides for the hammerhead's ampullae of Lorenzini, the extremely sensitive jelly-filled electroreceptors located around its mouth. Scientists believe these sensor cells act like metal detectors. They pick up weak electric fields, emitted by all living organisms, and then relay the signals to the shark's central nervous system to alert the dorsal-finned demon to prey camouflaged on the ocean floor. Which is really bad news for bottom-dwelling stingrays, another hammerhead staple.

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