Source : Webster's Revised Unabridged Dictionary (1913)

Bird's nest \Bird's" nest`\, or Bird's-nest \Bird's-nest\, n.
   1. The nest in which a bird lays eggs and hatches her young.

   2. (Cookery) The nest of a small swallow ({Collocalia
      nidifica} and several allied species), of China and the
      neighboring countries, which is mixed with soups.

   Note: The nests are found in caverns and fissures of cliffs
         on rocky coasts, and are composed in part of alg[ae].
         They are of the size of a goose egg, and in substance
         resemble isinglass. See Illust. under {Edible}.

Source : WordNet®

bird's nest
     n : nest where birds lay their eggs and hatch their young