The Collaborative International Dictionary of English v.0.48:

Caddow \Cad"dow\, n. [OE. cadawe, prob. fr. ca chough + daw
   jackdaw; cf. Gael. cadhag, cathag. Cf. Chough, Daw, n.]
   (Zool.)
   A jackdaw. [Prov. Eng.]
   [1913 Webster]