The Collaborative International Dictionary of English v.0.48:

Skua \Sku"a\, n. [Icel. sk?fr, sk?mr.] (Zool.)
   Any jager gull; especially, the Megalestris skua; -- called
   also boatswain.
   [1913 Webster]

WordNet (r) 3.0 (2006):

skua
    n 1: gull-like jaeger of northern seas [syn: skua, bonxie]