The descendants of escaped exotic pets could save endangered species. That’s what a team of scientists argues in a new paper, which proposes replenishing decimated populations of animals with their kin from the pet trade. One potential target is the yellow-crested cockatoo, one of the world's most prized household birds whose wild numbers are plummeting.

"This is a novel proposal for dealing with an increasingly common situation," says David Wilcove, an ecologist at Princeton University who was not involved with the work.

The yellow-crested cockatoo (Cacatua sulphurea) is a native of Indonesia's Sulawesi and Lesser Sunda islands. Its feathers are bright white, save for a shock of golden plumage at the crown, and the bird's medium size makes it ideal for a cage. The bird is a popular pet, but intense poaching has reduced its population to fewer than 7000 in the wild, earning the animal "critically endangered" status on the International Union for Conservation of Nature Red List of Threatened Species.

Ironically, there are too many yellow-crested cockatoos elsewhere. In Hong Kong, China, birds brought from Indonesia and sold as pets that escaped or were released have founded a growing, self-sustaining population of a couple hundred individuals in the city's woodlands. They're competing with native birds for nesting sites and food and are considered an invasive species.

So what if you could, so to speak, kill two birds with one stone? Wild bird trapping is illegal in Hong Kong, but if the city made an exception for the yellow-crested cockatoo and shipped the birds back to Indonesia, it could solve two problems at once.

That’s what ecologists Luke Gibson of the University of Hong Kong and Ding Li Yong of the Australian National University in Canberra propose in a paper appearing online today in Frontiers in Ecology and the Environment . The approach could work for other animals as well, including not only escaped pets, but species that were introduced outside their ranges for sport hunting or for domestication. Gibson and Yong identify 49 species—including birds, mammals, and reptiles—that could benefit from the same strategy. In some cases, captured feral animals could replenish the native populations; in others they could be funneled into the pet trade, hopefully replacing those captured illegally in their native habitat.

The list of species up for consideration includes the Philippine deer, now rare in the Philippines but damaging native vegetation on Guam and the Mariana Islands; a wild cow called the banteng, hunted to endangered status in Southeast Asia while there is a flourishing introduced population in Australia; and Burmese pythons—threatened in Asia, where the skin is used in traditional medicine—but now established in the Florida Everglades, where it is devastating foxes and rabbits.

"Introduced species are usually considered a problem,” Gibson says. “In these cases we consider them to be an opportunity to help buffer declining populations in their native ranges.”

The idea is "worth exploring," says Philip Seddon, a conservation biologist at the University of Otago in Dunedin, New Zealand. But the approach is "not likely to be a game changer for the management of either invasive or declining species, and carries some risk.”

Boosting species in their native ranges with animals from feral populations may be easier than introducing captive-bred animals, Wilcove says. "Captivity tends to diminish the ability of species to survive in the wild," he says; the prospects for translocating animals from one wild situation to another are "likely to be rosier." He adds that there will be numerous logistical hurdles to clear. Among other things, various permits will probably be required to trap, transport, and release endangered species.

In addition, selling captured feral animals into the wildlife trade could well increase demand for exotic pets, leading to more poaching, Seddon says. Gibson agrees that this would work only in very special cases. One is the Javan myna, which is so commonly kept as a caged bird in Indonesia that the wild population is now considered "vulnerable." Yet in Singapore, some 100,000 Javan mynas are displacing native birds from nesting and feeding sites, making them a pest. Capturing the birds in Singapore to supply the market in Indonesia could reduce pressure on the native population, Gibson says.

He and Yong stress that animals would have to be carefully checked for parasites and diseases before moving them to avoid exposing the native population to novel health threats.

One of the biggest challenges, the scientists say, is ensuring that the conditions that led to the decline of the native populations in the first place—typically habitat loss and lax protection—have been corrected. Otherwise, there's no point in translocating endangered species; on the contrary, for some species the best hope for avoiding extinction may be the safe havens they happened to find elsewhere on the planet.