The Collaborative International Dictionary of English v.0.48:

Bulldog \Bull"dog`\, a.
   Characteristic of, or like, a bulldog; stubborn; as, bulldog
   courage; bulldog tenacity.
   [1913 Webster]

   Bulldog bat (Zo'94l.), a bat of the genus Nyctinomus; --
      so called from the shape of its face.
      [1913 Webster]