The Wild File

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Q) Which animal makes the shortest migration?

Ned Balbo, Baltimore, Maryland

Migration can mean many things, and one scientist's definition might not jibe with another's. Some would call daily movements to and fro a form of migration; by this standard, the short-distance champ might be Convoluta roscoffensis, a species of marine flatworm that lives between grains of beach sand. These creatures migrate to the surface at low tide and burrow back down at high tide—a round-trip of less than eight inches. Then there are vertical migrations, as with Dall sheep, which might descend just a few hundred feet for the winter. But if you mean seasonal migration from one area to another, there are several you'd hardly notice. Many amphibians, like the Yosemite toad, travel less than a quarter-mile each spring, from meadows to the pools where they breed. Yet even this outdoes the lowly spotted salamander, whose annual pilgrimage takes it between 100 and 1,000 feet—still, that's a trek for a salamander.

Q) What is the Specter of the Brocken, and what causes it?
Mike Brown, Bellingham, Washington

Named for Germany's foggy 3,747-foot Brocken peak, where climbers have observed it for centuries, this optical effect—also called a mountain specter—usually occurs when you're high above a heavy cloud or fog bank and the sun is directly behind you—conditions rare enough that many mountaineers have never seen one, though airline passengers flying above clouds often witness specters of the planes they're on. If you ever see the Specter, which looks like a giant human figure, what you're witnessing is your shadow projected onto the cloud, usually surrounded by multicolored rings, or "glories," so as to resemble an angelic vision. But you haven't arrived at the pearly gates. As Jeffrey Lew, an atmospheric scientist at UCLA, explains, when sunlight hits the backs of water droplets and bounces back, it skims the surface of the drops; this can cause interference, which appears to us in the form of rings. "In the old days, only climbers saw them, and they got really freaked out," says Lew. "Now all you have to do is look out from your window seat as you nurse a bloody mary."

Q) Do whales shiver?
Jim Wells, Chicago, Illinois

The shivering mechanism is an involuntary heat-producing tremble seen in most mammals, but it's never been observed in whales. According to John Heyning, a marine biologist at the Natural History Museum of Los Angeles County, that's probably because whales don't need to shiver—their superefficient thermoregulation systems keep their body temperatures steady whether they're off the coast of Hawaii or in 30-degree Arctic water. The big guys' main defense, of course, is the subdermal layer of fatty tissue called blubber, which in a bowhead whale can be 20 inches thick. Leviathans also can shut off blood flow to their fins and flukes if they need to preserve core body heat, thanks to uniquely designed heat-regulating blood vessels. So if you ever do see a whale shiver, beware: The ghost of Ahab may be about.

Q) Why does water expand as it cools, while everything else seems to contract?
Lincoln Bleveans, Pawling, New York

Actually, water does contract until it gets down to about 39 degrees Fahrenheit. Like most matter, it's composed of molecules that move more slowly as heat is removed, causing the spaces between them to shrink. But water's a little funky. As the temperature approaches the freezing point, says John Chen, an applied scientist at Dartmouth, H2O molecules rearrange themselves in 3-D structures called lattices—series of six-sided rings of molecules connected by hydrogen bonding. Because water molecules can bond only at certain angles, these lattices are full of empty space, and the solid takes up more room than the liquid. The result? Your ice tray overfloweth.

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