Nightwings by Robert Silverberg

"Nightwings" is a science fiction novella by Robert Silverberg. It won the Hugo Award for Best Novella in 1969 and was also nominated for the Nebula Award in 1968. Nightwings is the first in a trilogy of novellas, the next two being "Perris Way" (1968) and "To Jorslem" (1969). These three works were later collected into a single novel in three sections, also titled "Nightwings".