König, C 2000. Owl vocalizations as interspecific differentiation patterns and their taxonomical value as ethological isolating mechanisms between various taxa. In: R.D. Chancellor & B.-U. Meyburg (eds). Raptors at risk: 781-794. Berlin and Blaine.
Citaat (p. 791):
"In the Peruvian Screech Owl (Otus roboratus) two “subspecies” differing very much in size have to be recognized. Their vocalizations are said to be similar (Johnson & Jones 1990), but there are differences, which might suggest specific separation. Like other screech owls, the Peruvian Screech Owl has two different songs: the territorial advertising (A-song) and a courtship, resp. aggressive song (B-song). In the dwarfish lowland form pacificus the A-song shows a distinctly slower sequence of notes in a trill than in roboratus, while in the latter the harmonics (overtones) are much more pronounced. In the B-song of pacificus the notes are accelerated towards the end of the short trill, first rising and finally falling in pitch (Hardy et al. 1989). In roboratus the B-song is longer and consists of equally-spaced “staccato”-notes uttered with a somewhat “undulating” quality in pitch (Figs. 18 and 19). Larger differences may be noted in the calls (see Johnson & Jones 1990!). I therefore cannot support the idea of Johnson & Jones (1990), who treat the taxon pacificus as subspecies of Otus roboratus, which is a relatively large Otus, living in mountainous regions. I suggest to give the dwarfish Pacific taxon from northwestern coastal Perú and western coastal Ecuador species rank, calling it Otus pacificus, the Tumbes Screech Owl."
