More on Hunting the Gowk from Infoplease:

• Hunting the Gowk - Hunting the Gowk (See April Fool.) Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894 ...
• Gouk - Gouk or Gowk. In the Teutonic the word gauch means fool; whence the Anglo-Saxon geac, a cuckoo, and ...
• Poisson d'Avril - Poisson d'Avril An April fool. The poisson d'Avril is the mackerel, and we have the ...
• April Fool - April Fool Called in France un poisson d'Avril (q.v.), and in Scotland a gowk (cuckoo). In ...
• Dictionary of Phrase and Fable: H - Definitions, origins, and illustrative excerpts for words, phases, and literary allusions starting with "H"