The Collaborative International Dictionary of English v.0.48:

Tropic \Trop"ic\, a.
   Of or pertaining to the tropics; tropical.
   [1913 Webster]

   Tropic bird (Zool.), any one of three species of oceanic
      belonging to the genus Phaethon, found chiefly in
      tropical seas. They are mostly white, and have two central
      tail feathers very long and slender. The yellow-billed
      tropic bird. Phaethon flavirostris (called also
      boatswain), is found on the Atlantic coast of America,
      and is common at the Bermudas, where it breeds.
      [1913 Webster]

WordNet (r) 3.0 (2006):

tropic bird
    n 1: mostly white web-footed tropical seabird often found far
         from land [syn: tropic bird, tropicbird, boatswain
         bird]