Source : Webster's Revised Unabridged Dictionary (1913)

Redtail \Red"tail`\ (-t?l`), n. (Zo["o]l.)
      (a) The red-tailed hawk.
      (b) The European redstart.

Source : WordNet®

redtail
     n 1: dark brown American hawk species having a reddish-brown tail
          [syn: {red-tailed hawk}, {Buteo jamaicensis}]
     2: European songbird with a reddish breast and tail; related to
        Old World robins [syn: {redstart}]