And a Cast of Thousands

Caribou
Each March or April, 129,000 caribou leave their wintering grounds on the Porcupine River in the Canadian Yukon, point their noses northwest, and don't stop until, ten days, 350 miles, and an entire mountain range later, they reach a shimmering strip of tundra in Alaska's Arctic National Wildlife Refuge. Here the sun never quite sets, and the cotton grass is vibrant enough to qualify as God's own green shag rug. During their six- to seven-week stay, the caribou give birth, devour the grasses, and escape the ubiquitous mosquitoes by thrashing in the icy waters of the Beaufort Sea. They fill the air with their curious moos, make the ground vibrate with their shovel-size hooves, and dodge the wolves and grizzlies that trail in their wake. But as soon as the calves can keep pace with their elders, the herds vanish like smoke, Yukon-bound. Unfortunately, the caribou calving grounds occupy a section of the refuge that oil companies in nearby Prudhoe Bay have been eyeing for years. This summer, Congress votes on an energy bill that may open the area to drilling—activity that environmentalists warn could disturb the pregnant cows and alter the migration pattern. Upshot: Visit soon.

See for Yourself: Several Alaska outfitters run trips that coincide with the caribou migration. Try Spring Caribou Basecamp, June 4­10, with Arctic Treks ($2,550 per person; 907-455-6502; www.arctictreksadventures.com). To go on your own, make arrangements with a bush-plane service (from $300 per hour) such as Coyote Air (800-252-0603) or Wright Air Service (907-474-0502), both in Fairbanks.
Mexican Free-Tailed Bats
With a 12-inch wingspan and a drag flap on its tail that retracts for faster flying, a Mexican free-tailed bat can easily cover 50 miles in a night. Each spring, 100 million of them migrate more than 1,000 miles from central and northern Mexico (and some from as far as Chile) to the limestone caves of the Texas Hill Country, where the females give birth to scads of inchlong bat pups. By May, the caves are crammed with bats—up to 300 per square foot—and carpeted yards-deep with crunchy guano. "The cave walls look just like fur," says Brian Keeley, a biologist with Austin-based Bat Conservation International. "The summertime maternity colonies of Texas are literally the largest, most dense concentrations of mammals on Planet Earth." Each day at dusk, the lactating mother bats emerge in massive cumulations of clicks, flaps, and flesh—a slam-dunk viewing opportunity for humans—to eat their own body weight (half an ounce) in insects. In September, they leave the colonyand ride the cold fronts south, to caves like Queva la Boca, near Monterey, Mexico.

See for Yourself: Naturalists from The Nature Conservancy of Texas lead tours at the Eckert James River Bat Cave near Mason, Texas, from May to September (no charge, 512-263-9201; www.tnc.org). Or try a guided trip to the state's biggest bat cave, Bracken, just north of San Antonio, with Bat Conservation International (free, for members only; membership $35 per year; 915-347-5970; www.batcon.org). Allergic to Texas? Watch the bats via the National Weather Service Doppler radar system at www.nws.noaa.gov.

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