The Collaborative International Dictionary of English v.0.48:

Chirp \Chirp\, v. i. [imp. & p. p. Chirped; p. pr. & vb. n.
   Chirping.] [Of imitative orgin. Cf. Chirk, Chipper,
   Cheep, Chirm, Chirrup.]
   To make a shop, sharp, cheerful, as of small birds or
   crickets.
   [1913 Webster]