Outside Online Archives

Outside magazine, December 1996

By Patrick Clinton

Basements, caves, and mines are nearly always cool, and yet animals burrow underground to keep warm during winter. What gives?
--Mark Crosby, New York, New York

The subterranean world is actually only cooler in summer, when the surface is warmed by the sun. In winter, underground spots are relatively warmer because of their "thermal inertia": Temperatures drop less quickly there, given the natural insulation from soil and the lack of windchill. (Large bodies of water also exhibit thermal inertia, but they're not very practicable for hibernation otherwise.) Dens only inches below ground--or below the snow, where there's permafrost--provide enough insulation that, thanks to the animal's own body heat, they're comfy all winter long.

Not that they're toasty. Most dens average maybe 20 or 30 degrees warmer than the surface. But burrowers don't want too much warmth anyway: Overly cozy temperatures speed up metabolism, which chews through stored body fat, which causes an animal to wake up unseasonably or, worse, to starve in its sleep. Heat also encourages the growth of parasites. And few animals wish to arise after a three-month hibernation hot, hungry, and covered with fleas.

What allows flying fish to truly "fly"? And what's the maximum distance they can go?
--Michael C. Rusch, San Clemente, California

Basically, they can fly because they have wings. All 40 or so species of tropical flying fish have oversize pectoral fins that when extended serve as airfoils. Unlike birds, they don't flap; they fling. Whooshing toward the ocean surface, flying fish beat their tails until they reach takeoff velocities of between 20 and 40 mph, outstripping some speedboats. They then launch themselves as much as 60 feet--to the great consternation of boaters nearby. Wayward Redwings, one of the most common species, have reportedly dive-bombed the chests of sailors, sent swimmers and waders reeling, and in one probably apocryphal story, whacked a woman so hard she died. More commonly they whir past drop-jawed cruise-line passengers and become the stuff of great UFO fish tales.

But why fly? "If you throw yourself out of the water, you get out of a predator's sight," says University of West Chester biologist Frank Fish (really), who has a sweetly empathic habit of referring to fish in the second person. "Since you control the flight path, you can curve off or decide when you drop back into the water."

Unless, of course, a fisherman is stationed nearby with a net. Some species are edible and highly sought-after--in which case, the fish's flight-to-flee response is likely to leave it, literally, high and dry.

Can giardia survive in stream ice?
--Alan Livingston, Denver, Colorado

Yes, at least some can--and when you're talking giardia, known to science as Giardia lamblia, not many is more than enough. Even a few in your gut will cause a host of famously nasty symptoms. And these protozoa, sad to say, are hardy as hell. When outside a host--as when suspended in a mountain stream--they take the form of cysts, tough-shelled microscopic balls. Cold doesn't kill them. Freezing and thawing can, but only if the cyst gets crushed by ice crystals. Don't bet on it. If you want to swig stream ice, filter or heat it first. The water has to reach the critter's "thermal death point" of 135 degrees Fahrenheit. "Heat it until it begins to steam," says microbiologist Ernest A. Meyer of Oregon Health Sciences University, editor of the forthrightly titled book Giardiasis. Then, to be safe, let the water boil. This will not only kill any bacteria present, but will ensure, gratifyingly, that every giardia you've scooped up crosses the great thermal-death-point divide.

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