Skyler Kardell gets to watch birds for a living, in his job as a coastal steward on Tuckernuck Island, part of the town of Nantucket, Massachusetts. While patrolling the beach on September 5, observing terns, the 18-year-old spotted what initially looked like a great blue heron, a waterbird commonly seen there. But on closer look, something was off—it appeared smaller and paler.

“It had a shorter neck, shorter legs, and shorter bill than a great blue,” Kardell says. In fact, it looked like a gray heron, though Kardell had only seen one before in a book. But these birds are native to Eurasia and Africa.

“I had my suspicions right from the get-go, but because this identification poses a number of issues,