FOCUS ON NATURE

Prairie Dogs Look Askance at Black-footed Ferret Comeback

In a prairie-dog town, bad news travels fast. Standing atop the mounds of dirt surrounding the mouths of their burrows, prairie dog sentinels use yips and barks to warn the neighborhood that a coyote is nearby or a red-tailed hawk is overhead. Researchers believe the prairie dogs have specific calls for specific threats.

If so, “black-footed ferret” must be a four-letter word in prairie dog talk.

The ferrets have a simple diet-prairie dogs. Coyotes and hawks will snatch a careless prairie dog in broad daylight, but they mostly eat other small mammals. Not so the ferret. To make matters worse for the daylight-loving prairie dog, the black-footed ferret prowls after dark. So, when Mr. and Mrs. Prairie Dog have settled down for the night safe from Wiley E. Coyote, the skulking black-footed ferret goes dashing from burrow to burrow, sniffing along pitch-black tunnels until it finds its sleeping supper and takes up residence.

Mind you, this is not your kid-brother’s pet. It’s about the same size-maybe 2 feet long and 2.5 pounds-but in the wild, the black-footed ferret is all tooth and fury-one ferocious little carnivore.

So Arizona’s prairie-dog population must have thrown a heck of a party when the last black-footed ferret disappeared from the state’s grasslands.

But the party proved premature.

These days, the Arizona Game and Fish Department is making a concerted effort to bring back the black-footed ferret. West of Seligman, State Route 66 follows the southern edge of the Aubrey Valley, with prairie-dog mounds visible on both sides of the highway. When the sunlight is just right, metal fences gleam in the middle of the valley to the north-pens holding black-footed ferrets awaiting a return to the wild.

Once upon a time, their range extended from the Yukon to the American Southwest. But progress, poisons and plague decimated prairie dogs and ferrets as farmers and ranchers wiped out the prairie dogs that sometimes turned the grassy plains into hole-studded hazards for cattle. When the campaign of extermination eased, the prairie-dog populations gradually recovered; black-footed ferrets did not. By 1979, they were listed as extinct.

However, in 1981, biologists discovered a few surviving black-footed ferrets hanging on near Meeteetse, Wyoming. When canine distemper swept through even this final population in 1986, biologists rounded up the last 18 left alive to prevent extinction.

The U.S. Fish and Wildlife Service and state agencies like Arizona Game and Fish established a plan to save the ferrets. In September 1996, wildlife managers released 35 black-footed ferrets in the Aubrey Valley. To provide protection and time to get used to their surroundings, biologists built acclimation pens of chicken wire, trenched 18 to 24 inches around the perimeter, so ferrets can’t dig their way out and foxes, coyotes and badgers can’t dig their way in. The pens have an electrically charged wire running close to the ground powered by solar panels and storage batteries. Another set of crisscrossed wires overhead wards off hawks and eagles.

Built on top of an existing prairie-dog town, the acre-sized pens’ interior fences divide into four separate conditioning areas, each with a buried nest box that emulates natural conditions.

Daily, the biologists visit each nest box to feed the ferrets and to remove their scat. The scat provides an early indicator of health problems. After a couple of weeks of monitoring and feeding the ferrets chunks of prairie dog, biologists lock the ferrets out of their nest boxes, forcing them to learn how to navigate the prairie-dog burrows and tunnels for food.

After the ferrets make three live kills, they are released into the wild. They breed in March and April, and biologists conduct a mid-gestation follow-up check at about 21 to 23 days. At 42 to 45 days, the ferrets give birth to three to five kits.

Because the black-footed ferret is nocturnal, keeping track of the wild population requires special measures. Nocturnal animals have a thin reflecting membrane behind the retina called the tapetum lucidum, which causes their eyes to shine visibly when a light hits them. Different species have different colored eye shine. The eyes of a black-footed ferret shine emerald green.

So biologists and volunteers count ferrets by driving dirt roads or hiking across country carrying heavy batteries and lights with which they sweep the landscape, looking for emerald-green eye shine. When they find one, they capture the ferret by placing a custom-made, baited trap into the burrow. The biologists keep the ferret just long enough for identification and inspection.

Because of a wet winter in 2004-05, prairie-dog numbers are higher in the Aubrey Valley than they have been for the last seven years. The most recent count shows that prairie dogs inhabit more than 43,000 acres there, equating to about three prairie dogs per acre. As for the ferrets, the most recent count in September 2005 identified 68 ferrets living in Aubrey Valley, although biologists suspect the population is larger than the numbers indicate and are encouraged by data that show numbers are on the rise.

In the meantime, the prairie dogs of the Aubrey Valley have discovered to their dismay, that ferret is just another four-letter word. AH