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]

The Collaborative International Dictionary of English v.0.48:

Marline \Mar"line\, n. [LG. marlien, marling, or D. marling,
   marlijn, fr. D. marren to tie, prob. akin to E. moor, v., and
   lijn line: cf.F. merlin. See Moor, v., Line.] (Naut.)
   A small line composed of two strands a little twisted, used
   for winding around ropes and cables, to prevent their being
   weakened by fretting.
   [1913 Webster]

   Marline spike, Marling spike (Naut.), an iron tool
      tapering to a point, used to separate the strands of a
      rope in splicing and in marling. It has an eye in the
      thick end to which a lanyard is attached. See Fid.
      [Written also marlin spike]

   Marline-spike bird. [The name alludes to the long middle
      tail feathers.] (Zool.)
   (a) A tropic bird.
   (b) A jager, or skua gull.
       [1913 Webster]