When the birds fly south

by Stanton A. (Stanton Arthur) Coblentz

"When the Birds Fly South" by Stanton A. Coblentz is a lost race fantasy novel first published in 1945. American adventurer Dan Prescott stumbles upon a hidden valley in Afghanistan inhabited by the Ibandru, a mysterious winged people. He falls in love with Yasma, one of their own, and they marry. But when autumn arrives, the Ibandru prepare to fly south with migrating birds, forcing Prescott to make a desperate choice that will forever alter his fate.