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]

The Collaborative International Dictionary of English v.0.48:

Jager \Ja"ger\, n. [G. j[aum]ger a hunter, a sportsman. Cf.
   Yager.] [Written also jaeger.]
   1. (Mil.) A sharpshooter. See Yager.
      [1913 Webster]

   2. (Zool.) Any species of gull of the genus Stercorarius.
      Three species occur on the Atlantic coast. The jagers
      pursue other species of gulls and force them to disgorge
      their prey. The two middle tail feathers are usually
      decidedly longer than the rest. Called also boatswain,
      and marline-spike bird. The name is also applied to the
      skua, or Arctic gull (Megalestris skua).
      [1913 Webster]