What does "jager" mean?

Jager: (Zoöl.) 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).