Thanks to Xavier Basora for his prompt and interested reply to my query. 'Owl' in Catalan is òliba or, less commonly, xibeca (x is Catalan in pronounced 'sh' or 'ch'). Both of these strike me as a bit of a stretch for onomatopoeia, though òliba might be possible. When Catalan speaking owls hoot the verbs are cridar [like Italian gridare?], udolar [whoo-oo-ooo-dolar!] or ganyolar [??].

Update: Mr. Basora settles my questions and speculations.