The Collaborative International Dictionary of English v.0.48:

Chitter \Chit"ter\, v. i. [Cf. Chatter.]
   1. To chirp in a tremulous manner, as a bird. [Obs.]
      --Chaucer.
      [1913 Webster]

   2. To shiver or chatter with cold. [Scot.] --Burns.
      [1913 Webster]

WordNet (r) 3.0 (2006):

chitter
    v 1: make high-pitched sounds, as of birds [syn: chitter,
         twitter]