WOLF: Yeah, it's beautiful. SUMMERS: Adrian Wolf knows birds. He once studied a threatened species called the streaked horned lark for over 10 years. WOLF: It has a piece in my heart, and it's little ...

ADRIAN WOLF: The Swainson's thrush. It's a lovely, ethereal sound. (SOUNDBITE OF SWAINSON'S THRUSH CALL) WOLF: Yeah, it's beautiful. SUMMERS: Adrian Wolf knows birds. He once studied a threatened ...