The Collaborative International Dictionary of English v.0.48:

Merlin \Mer"lin\, n. [OE. merlion, F. ['e]merillon; cf. OHG.
   smirl, G. schmerl; prob. fr. L. merula blackbird. Cf.
   Merle.] (Zool.)
   A small European falcon (Falco columbarius, syn. Falco
   lithofalco, or Falco aesalon). In North America called
   also pigeon hawk.
   [1913 Webster +PJC]