The Collaborative International Dictionary of English v.0.48:

Flacker \Flack"er\, v. i. [OE. flakeren, fr. flacken to move
   quickly to and fro; cf. icel. flakka to rove about, AS.
   flacor fluttering, flying, G. flackern to flare, flicker.]
   To flutter, as a bird. [Prov. Eng.] --Grose.
   [1913 Webster]