When the Birds Fly South is a lost race fantasy novel by American writer Stanton A. Coblentz, defined as a "significant tale ... involving avian theriomorphy.

"[1] It was first published in hardcover by The Wings Press, Mill Valley, California in 1945 and reprinted in 1951.

Dan Prescott, an American adventurer, discovers the hidden valley of Sobul in a mountainous region of Afghanistan, inhabited by a strange race of winged people known as the "Ibandru".

When fall comes, however, the Ibandru abandon their valley to fly south with the birds for the winter.

Unable to bear the loss of Yasma, Prescott pleads with her to remain with him rather than participate in the traditional migration, with tragic consequences for his marriage.