On the first day of a new project to study the long-billed curlew, North America’s largest shorebird, ornithologist Jay Carlisle came across something upsetting: a dead curlew with a bullet hole through his head.

It was 2009, and populations of the knobby-kneed bird with an eight-inch beak were struggling in southwestern Idaho, though no one was sure why. Shooting these birds is illegal under federal law, but Carlisle, who’s the research director of the Intermountain Bird Observatory, a project of Boise State University, soon found out that it was a common occurrence.