The Collaborative International Dictionary of English v.0.48:

Egg-bird \Egg"-bird`\, n. (Zo["o]l.)
   A species of tern, esp. the sooty tern (Sterna fuliginosa)
   of the West Indies. In the Bahama Islands the name is applied
   to the tropic bird, Pha["e]thon flavirostris.
   [1913 Webster]