On an August day almost four years ago, Joe Harkness stood at Blakeney Point, a nature reserve in Norfolk, England. Rain poured along the North Sea coastline, a hotspot for observing avian migrants, and Harkness had his face turned to the sky as birders often do. Soon, it wasn’t just water coming down; flocks began descending, too. “I find it difficult to put into words how it feels to be standing while it's raining birds,” Harkness says. “It was unbelievably magical, and when I got back, I wrote my [first] blog.” The phenomenon Harkness experienced, called a “fallout” of birds, occurs when winds funnel migrating species toward the shore where they hit a wall of rain and are forced from the sky. For Harkness, it was a climactic moment. He began writing a blog called “Bird Therapy,” with his first post documenting the awe-inspiring event and the positivity he felt through birding. After many more revelations and entries, Harkness decided to spin the...