Whether it’s because we destroy their habitats, discombobulate them with city lights, or allow cats into their midst, most wild birds want nothing to do with humans. But purple martins—shimmery, blackish-bluish swallows native to North America—just can’t get enough. For centuries, the species has gradually abandoned its homes in the wild for birdhouses we’ve built. An entire subspecies of the bird now nests exclusively in human-made boxes; east of the Rocky Mountains, “there are officially no purple-martin colonies that exist outside of that,” says Joe Siegrist, the president of the Purple Martin Conservation Association. Modern martins have become downright trusting of people. Some will even let humans reach into their nest and pick up their chicks—an intrusion that would send other birds into a screeching, pecking rage. “They’re the most docile species I’ve ever worked with,” says Blake Grisham, a wildlife biologist at Texas Tech University. And the more we build birdhouses and interact with martins, the more they seem to thrive. “It’s totally the opposite of our default in wildlife management,” Grisham told me. …