Earlier this year, Chicago residents were delighted to watch a pair of Great Horned Owls take up residence in Lincoln Park, a swath of green along the city’s edge, and thrilled in seeing the family grow with the addition of an owlet in spring. “They were not distant creatures that you had to look through binoculars to see,” says Dana Harbaugh, who chairs the advocacy committee of the Chicago Bird Alliance. “They were right there, in the city, in this amazing green space.” Then, one by one, the owls started dying. First the adult male, sometimes known as “Papa Owl,” in early April; a few weeks later the pair’s owlet, found dead near the pond where the trio spent their time. Finally, in May, the adult female owl was discovered bleeding out on the sidewalk in front of a nearby home. Though full reports on these deaths are still in the works, local rehabbers strongly suspect that rodenticides played a role. If confirmed, that would place the Lincoln Park owls in a...