The Collaborative International Dictionary of English v.0.48:

Fork-tailed \Fork"-tailed`\, a. (Zool.)
   Having the outer tail feathers longer than the median ones;
   swallow-tailed; -- said of many birds.
   [1913 Webster]

   Fork-tailed flycatcher (Zool.), a tropical American
      flycatcher (Milvulus tyrannus).

   Fork-tailed gull (Zool.), a gull of the genus Xema, of
      two species, esp. X. Sabinii of the Arctic Ocean.

   Fork-tailed kite (Zool.), a graceful American kite
      (Elanoides forficatus); -- called also swallow-tailed
      kite.
      [1913 Webster]