CHICAGO — The first attempt to reintroduce black-footed ferrets into the wild flopped.

Coyotes gobbled up the polecats, which once lived across the Great Plains but were on the brink of extinction, because the cage-born ferrets never learned about natural predators, how to hunt prairie dogs or to take over their burrows for homes.

The second time around, biologists used stuffed owls, remote-controlled "robo-badgers" and domestic dogs to chase the ferrets around, teaching them fear. They also brought in prairie dogs to teach the ferrets to catch food and live underground.

With that help, the ferrets regained a solid foothold.

"These are some of the problems we deal with," said Lincoln Park Zoo zoologist Rachel Santymire at a conference Thursday of about 100 biologists and nature resource managers from zoos, nonprofits, nature centers, universities, state governments and Chicago-area forest preserves.

Releasing endangered and threatened species to create self-sustaining populations and rebuild balanced ecosystems is often the goal in saving animals from extinction. But the endeavor can be risky, complex and expensive, with variables ranging from disease to inbreeding to the whims of politicians holding the purse strings for projects.

"It's not as easy as dropping ferrets out the window," Santymire said.

The two-day conference was co-hosted by the zoo and the U.S. Fish and Wildlife Service and touched on worldwide examples of reintroduction from apes to insects.

Picking winnable battles and preparing well are crucial, particularly with limited funding for conservation, said Mike Redmer, a herpetologist.

"If we're going to do this we have to be more responsible with the resources, not just the animals, with endangered species we have precious few of them, but also the financial resources can't be wasted," Redmer said.

The success stories include the gray wolf and the black-footed ferret, which went from just 18 in captivity to a wild population of about 600 today in a dozen locations from Mexico to Montana.

The failures include the 32 woodland caribou released in Maine in 1988 and 1989 but dead by 1990, killed by black bears and brain worm. Another example is the herd of Arabian oryx, an elegant desert antelope, which grew to 400 in Oman in the Middle East before poachers wiped them out in the late 1990s.

Michael Amaral, a senior endangered species specialist with the service's New England field office, detailed a decades-long project to bring back the American burying beetle, which once stretched across the eastern United States but has dwindled to tiny populations in Oklahoma and an island off Rhode Island. The red and black, 1 1/2-inch-long beetle, which feeds and breeds on dead animals it buries underground, has been reintroduced to Nantucket Island.

"Look at this magnificent animal," he said as a slide of the beetle projected on screen appeared the size of a rhino. "Some people say insects don't have charisma."