The origins of this name are unkonwn.It could possibly have been given because the smugglers conducted their activity at night. Maybe they communicated warnings to their group members by imitating an owl's hoot. There was also a crime against the public trade of 'transporting wool or sheep out of the Kingdom.' Again the offenders normally carried this out at night, so Owlers could also refer to this.
The writer, Parliamentarian and social blogger of his day, Narcissus Luttrell's report (in his diary) of 1699 was one of the first documents to use this term. The diary is also a record of major events in Parliament, diplomacy and the arts.
Pirates and smugglers may well have used a 'slang or cant language' and codes to confuse outsiders. An example is the word 'pad' which was said to be slang used by smugglers, highwaymen and footpads, to mean 'highway.' To test your skill at cracking a lost treasure code click here