Q: What animal has the greatest migratory range?
—Jordan Linville, Wye Mills, Maryland
A: The Arctic tern is the champion globetrotter, a big deal for an animal that measures only a foot long. Each fall, the white pelagic bird with pointed wings (and extremely toned pectoral muscles) flies about 22,000 miles from the Arctic Circle to the Antarctic Circle, "wintering" in the extreme south and thus seeing more
daylight than any other bird. To navigate between their breeding grounds in the north and their feeding grounds in the south, they follow an elder's lead and an inherited internal map. Arctic terns rarely rest during their three-month, over-ocean commute. They stay aloft by riding the Gulf Stream and other trade winds, and divebomb for shrimp, krill, or
plankton blooms when hungry. Unfortunately, such prolonged airtime also works to their disadvantage: "At only two pounds, they get royally buffeted by storms," says Russ Greenberg, head of Washington D.C.'s Smithsonian Migratory Bird Center. On the other hand, by the advanced age of 30, these long-lived birds will have winged almost a million
miles—enough frequent-flyer mileage for ten free first-class Anchorage-Santiago round-trips.
Q: I've heard that 90 percent of all tornadoes hit the United States. Why are we such a good target?
—Robin Angstadt, Denver, Colorado
A: "Eighty percent is probably more accurate," says Harold Brooks, a research meteorologist with the National Severe Storms Laboratory in Norman, Oklahoma. He estimates that 1,500 tornadoes per year touch down in the United States, compared to 150 in Europe, 20 in Canada, and a couple dozen more in places scattered around
the globe. The reason we're the biggest twister-magnet, explains Brooks, is that there's no other region like the Plains, with a warm body of water to the south and a high, wide mountain range to the west. In April and May especially, heated moist air from the Gulf of Mexico blows in at a couple thousand feet and meets dry air crossing the Rockies at 5,000
to 30,000 feet. The two currents create a rotating column of air that can generate 318-mile-per-hour winds, debark trees, and fire cars across the sky like missiles. Granted, this is as grim as it gets. Most American tornadoes hover around 100 miles per hour, and typically touch down in "Tornado Alley"—sections of Texas, Oklahoma, Colorado, Kansas,
Nebraska, and South Dakota. Pity Pauls Valley (pop. 6,150), 50 miles south of Oklahoma City. With an average of one tornado every three years, it's the twister capital of the world.
Q: How much rain is required to make a rainbow? Is there a raindrops-per-cubic-inch threshold that's necessary for a rainbow to be visible?
—Andrew Heiz, Flushing, New York
A: The brightness of a rainbow has more to do with the size of individual water droplets than with the density of rainfall. As long as you've got enough moisture to blur the horizon, white sunlight enters each prismatic raindrop, divides into a spectrum, and then each minirainbow makes a U-turn by reflecting off the back of
the drop toward your eyes. In small raindrops, half the width of a human hair, these beams of color overlap and interfere with each other to create a white rainbow, what's known to atmospheric physicists as a "fog bow." Rainbows with larger drops, about the size of BBs, display vivid violet, green, and red stripes. However, if the drops are too large
they'll collide with each other, break apart, and form a bow that shimmers. Of course, Mother Nature rarely lets loose a shower of uniform raindrops, so it's nearly impossible to predict the color and intensity of a rainbow—which, after all, is part of the charm.
Q: Perhaps you can resolve a dispute between myself (short) and a friend (tall). He claims a tall man can do fewer pull-ups than a short man because the tall man pulls a longer distance to the bar. I say a tall man puts forth the same effort, since taller men have bigger muscles. Who is right?
—Tim Anderson, St. Coal Valley, Illinois
A: Assuming a similar level of fitness, diet, and body shape, the taller person has a disadvantage when it comes to pull-ups. But don't let your pal gloat—the height handicap has nothing to do with distance from chin to bar, but rather with a frustrating fact of physiology: When you grow, you add weight in all
directions—getting thicker and taller—but your muscle gets stronger only as it grows thicker. "Muscle force has been found to correspond to the two-dimensional cross-section of a muscle, measured across the muscle fibers," explains University of California-Davis exercise biology professor Keith Williams. "Weight is proportionate to body volume,
measured in three dimensions." Simply put, taller people have bigger muscles, but they have less muscle to lift more weight. To illustrate gravity's triumph over human development, look no further than the women's division of the American Sport Climbing Federation Nationals. Last June, the muscle-bound, five-foot, four-inch champ Tiffany Campbell nearly
lost to four-foot, nine-inch Tori Allen—a 65-pound 12-year-old.
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