The Collaborative International Dictionary of English v.0.48:

Birk \Birk\, n. [See Birch, n.]
   A birch tree. [Prov. Eng.] "The silver birk." --Tennyson.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Birk \Birk\, n. (Zool.)
   A small European minnow (Leuciscus phoxinus).
   [1913 Webster]