The Collaborative International Dictionary of English v.0.48:

Wader \Wad"er\, n.
   1. One who, or that which, wades.
      [1913 Webster]

   2. (Zool.) Any long-legged bird that wades in the water in
      search of food, especially any species of limicoline or
      grallatorial birds; -- called also wading bird. See
      Illust. g, under Aves.
      [1913 Webster]

WordNet (r) 3.0 (2006):

wader
    n 1: any of many long-legged birds that wade in water in search
         of food [syn: wading bird, wader]