The Collaborative International Dictionary of English v.0.48:

Hagdon \Hag"don\ (h[a^]g"d[o^]n), n. (Zool.)
   One of several species of sea birds of the genus Puffinus;
   esp., Puffinus major, the greater shearwarter, and
   Puffinus Stricklandi, the black hagdon or sooty shearwater;
   -- called also hagdown, haglin, and hag. See
   Shearwater.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Shearwater \Shear"wa`ter\, n. [Shear + water; cf. G.
   wassersherer; -- so called from its running lightly along the
   surface of the water.] (Zool.)
   Any one of numerous species of long-winged oceanic birds of
   the genus Puffinus and related genera. They are allied to
   the petrels, but are larger. The Manx shearwater (Puffinus
   Anglorum), the dusky shearwater (Puffinus obscurus), and
   the greater shearwater (Puffinus major), are well-known
   species of the North Atlantic. See Hagdon.
   [1913 Webster]