Australia is like a pet shop with its doors thrown open. Strange marsupials, frilled lizards, and gaudy birds dot the countryside. And many of Australia’s birds, from cockatoos to budgies, are pet shop staples. Until the mid-1980s, trappers collected 11 species of finches from the grasslands of northern Australia, earning up to $11 per bird in the pet trade.

The most valuable of these was the Gouldian Finch, a tiny, outrageously colorful bird that is now one of the most popular cage birds in the world. “I’m always amazed wherever I go; I walk into a pet shop and Gouldians are there,” said Sarah Pryke, a biologist at Macquarie University in Sydney, Australia, who has worked on the finches since 2005. She studies them because, despite their ubiquity behind bars, Gouldian Finches are nearing extinction in the wild—a sad paradox that afflicts other beloved cage birds, including the Java Sparrow and South America’s Red Siskin. Learning how to bring back wild populations, and discovering the ways in which their caged counterparts can and cannot help, is an ongoing puzzle. Fortunately for Gouldians, recent focus on the birds’ unusual nesting sites may help turn the tide.

Hundreds of thousands of Gouldian Finches used to live in Australia’s tropical savannas, but by the 1980s their numbers had crashed to 2,500 or fewer. The pet trade was not so much to blame as the bird’s fussiness and naïveté, Pryke said. Gouldian Finches eat the seeds of only about a dozen species of grasses; they nest only in deep, hollow branches of two species of eucalyptus trees; and if they are bred in captivity, they emerge into the wild clueless about predators.

Brad Congdon, of James Cook University, was part of an early project to release captive-bred birds from an aviary at the Jabiru Safari Lodge in northern Queensland. When they first opened the doors, the birds didn’t even wake up. When they did leave, “they were like lollipops for raptors,” Congdon said. “They just did not know what to do when any predators came around.”

Captive-bred birds can have problems in the wild, said Eduardo Iñigo-Elias, who leads the Cornell Lab’s Neotropical Conservation Initiative. For example, endangered Puerto Rican Parrots were raised using Hispaniolan Parrots as surrogate parents. The chicks developed just fine, but they only learned the dialects of their foster parents and failed to recognize their own species once released.

So even though Gouldian Finches breed well in captivity, issues with genetics, behavior, and disease mean they can’t be used to restock the wild population. Instead, Pryke studies captive birds to learn about wild ones. A breakthrough came when her team focused on nest sites, which for years hadn’t been studied because tree holes seemed plentiful on the Australian savanna. But it turns out they weren’t the right kind of tree holes.

“Gouldians are really fussy about what they’ll use,” Pryke said. “They like a very small entrance, and they like a very deep, long entrance, and they pretty much won’t breed in anything else.” So Pryke and her colleagues invented a nest box that looks like a cross between a bluebird box and a didgeridoo. “They love it really, really dark, and they love to run down this sort of tunnel into their box,” Pryke said.

The first few years of results have been promising. In places where just 40 percent of adults nested each year, the addition of nest boxes pushed the nesting rate to 90 percent, and also reduced predation and increased brood sizes, Pryke said.

Using teams of graduate students and volunteers, Pryke has now built more than 3,000 of these boxes, and Gouldian Finch populations in her study areas have tripled. “It suggests that if we can get the environment right, [nest boxes] could probably help to increase these birds back to good numbers,” she said.