The Collaborative International Dictionary of English v.0.48:

Red-tailed \Red"-tailed`\ (-t?ld`), a.
   Having a red tail.
   [1913 Webster]

   Red-tailed hawk (Zool.), a large North American hawk
      (Buteo borealis). When adult its tail is chestnut red.
      Called also hen hawck, and red-tailed buzzard.
      [1913 Webster]

WordNet (r) 3.0 (2006):

red-tailed hawk
    n 1: dark brown American hawk species having a reddish-brown
         tail [syn: redtail, red-tailed hawk, Buteo
         jamaicensis]