Uropygial /(?)/

U·ro·pyg·i·al

Uropygial

a.
  1. Of or pertaining to the uropygium, or prominence at the base of the tail feathers, in birds. (Anat.)

Phrases & Compounds
Uropygial gland
a peculiar sebaceous gland at the base of the tail feathers in most birds. It secretes an oily fluid which is spread over the feathers by preening.