JACKSON, Wyo. (AP) — Gus Smith was walking his German shorthair not far from his Moose home one Saturday in late May when euphoria flew by in a flock.

Fellow birders would best appreciate his experience.

Out on foot near the Chapel of Transfiguration, Smith suddenly found himself engulfed by black rosy finches. That's an alpine species of songbird that's normally found only above treeline, yet there he was, at below 6,500 feet, surrounded by perhaps 300 to 350 of them.

"They're just doing that cloud thing," Smith recounts. "They were right there — they go right through us."

Even retelling the...