If you wonder what lurks within some curious crevice, use the size, shape, and structure to determine the possible residents (see "Whose Hole?" on page 40). A den site littered with fur, bones, and partially eaten prey is likely where a fox, coyote, or wolf is raising young. Move along so you don't disturb the babies. Otherwise, find a comfortable spot, preferably downwind of the hole, and wait for a little head to pop out, confirming your guess. Sit quietly, and keep these clues in mind:
Fresh dirt piled by a hole indicates an active marmot or woodchuck house. Quick-escape holes are dug from the inside and don't have the telltale mound.
A snake slithering out of a hole is just a visitor-or more likely a snacker-not a resident. Snakes don't dig holes, but will check rodent burrows for food.
Skunks often defecate near their holes. You'd better step lightly, or move away, if you spy 3/8- to 3/4-inch piles (similar in shape to dog scat) that contain lots of insect parts.
Why build when there's a den in move-in condition? That's what skunks, mink, and raccoons do. These animals often take over abandoned dens, while opossums and foxes have been known to move in with the original owner of a multichambered den.
Bear in mind that you might not even see some holes. Many pocket mice of the Southwest plug their entrance holes with soil during the day to stave off moisture loss. Tarantulas read the same book: During the day, they weave a film of silk that covers their burrows.
"On the ground," declares Merlin, "everybody has a trick up their sleeve."
Or, of course, down their hole.
A Field Guide to Desert Holes, by Pinau Merlin (Arizona-Sonoma Desert Museum Press, 520-883-3028; $7.50). Animal Architects: How Animals Weave, Tunnel, and Build Their Remarkable Homes, by Wanda Shipman (Stackpole Books, 800-732-3669; $16.95). Stokes Nature Guides: A Guide to Animal Tracking and Behavior, by Donald and Lillian Stokes (Little, Brown, 800-759-0190; $15). Tracking and the Art of Seeing: How to Read Animal Tracks and Sign, by Paul Rzendes (HarperCollins, 800-331-3761; $25).
Ground-dwelling wasps recently sent North Carolina writer Eddie Nickens to the emergency room, sharpening his interest in zoological aperture ecology.
Use a mirror to reflect sunlight into the hole instead of putting your face near the hole to see inside it. The beam is far brighter than that of a flashlight.
Look for shed hair or hair caught on sharp objects like rocks and tree roots around the hole opening to identify the occupant.
Carry a small measuring tape. Field estimates of hole dimensions often are way off.
Get too close to a suspected natal den. You might force the mother to move her young. Instead, observe with binoculars or a spotting scope.
Put your face close to a suspected animal den. You might inhale the eggs of the host's parasites.
Probe holes with sticks, stems, fingers, or hiking poles. If the occupant is an insect or young animal, you might injure it.