For endangered species, even a small boost in numbers can help shift the needle away from extinction. But isolating animals for safe breeding comes with a cost. Captive “insurance populations” of endangered species, like the protected group of Puerto Rican Parrots, can lose their survival edge, both behaviorally and genetically, in just a few generations. Once they become easy prey, they’re less likely to survive if released.

This situation has left some conservationists in an ethical bind. So far, wildlife-reintroduction programs have been hesitant to embrace an approach where live predators possibly injure or kill one animal for the sake of teaching many—even if, as in the safety-vested parrot’s case, the animal that’s attacked isn’t endangered. But White’s results seem promising. And researchers behind these programs know that pampering wildlife in captivity won’t help if the species can no longer make it on its home turf.

Earlier this year, on an island thousands of miles from Puerto Rico, another group trying to bring back a critically endangered bird called White for advice. The group, based primarily on Hawaii’s Big Island, had released five Hawaiian crows—raven-like birds with bristly feathers framing dark beaks—from a captive flock into their native forest, a place the species had not been in nearly 15 years. But within a week, three of the crows had died. Two were killed by their native predator, the Hawaiian Hawk, or ‘io.

Having some deaths in a reintroduction program, especially early on, is not unusual, says Alison Greggor, a researcher with San Diego Zoo Global, one of a few institutions collaborating to reintroduce the crows. Nevertheless, this initiative—known as the the ‘Alalā Project, after the crows’ native name—collected the surviving birds back into captivity, and vowed next time would be different. While the group had attempted antipredator training before releasing the crows, they realized it wasn’t rigorous enough. For these ‘alalā, approximately five generations removed from the wild, to have a chance at survival, the species needed to relearn to outwit its old adversary.

White advised his colleagues in Hawaii to show the ‘alalā that hawks mean business, and recommended a similar approach to the training he employs with the Puerto Rican Parrots. If the ‘alalā were going to watch a non-native bird get attacked, “I told them that you don’t need to worry about a vest,” White says. “Just go ahead and have the real experience.”

But the “real experience”—allowing a hawk to actually kill a bird in front of the ‘alalā, as opposed to merely simulating an attack—might not go over well with everyone. Animal-welfare permits and public perception are concerns, and the ‘alalā is revered as a family guardian in Native Hawaiian culture. Besides, the ‘Alalā Project wanted to take a “data-driven approach” to the training and adapt it to the learning style of crows, which are notoriously perceptive, social birds. To narrow down the best techniques, the group performed pilot trials, observing how the crows reacted to multiple scenarios, including one in which a hawk attacked live prey.