The Collaborative International Dictionary of English v.0.48:
Owler \Owl"er\, n. [From Owl, v. i.] One who owls; esp., one who conveys contraband goods. See Owling, n. [Obs. or Prov. Eng.] --T. Brown. [1913 Webster]Bouvier's Law Dictionary, Revised 6th Ed (1856):
OWLER, Eng. law. One guilty of the offence of owling.