Vocal communication of the brown hawk owl Ninox scutulata in Japan

Abstract

Vocalizations of the largely nocturnal Japanese Brown Hawk Owl Ninox scutulata japonica were studied, with particular reference to the function of vocal communication. The adult owls were found to have thirteen types of vocalization and three non-vocal sounds with the possible addition of one other vocal sound. Nestlings had four vocal and one non-vocal sound. The development of the vocal repertoire was also studied from captive juveniles. Most of the vocal repertoire was recorded and sonagraphically analysed, and their behavioural contexts were investigated to give an idea of their various functions. The main function of primary calls was in interactions with conspecific birds from a distance. The daily calling of territorial males was not time-related and appeared to be greatly influenced by the intraspecific environment. Seasonal production was concentrated during breeding activity, showing four peaks which are discussed in terms of territorial, sexual and family interactions. The unusual vocal activity of a replacing male was studied and gave valuable additional information. Primary calls were also considered to convey different types of information through variation in their physical structure. From the examination of calls in natural conditions and in aggressive responses to playback, variations of frequency and rate were related to location in the territory, the breeding cycle and the caller's motivational state.There were consistent individual variations in temporal and frequency features of the calls. Playback of neighbour and stranger's calls and that of the mate and other females' calls at various locations in the territory elicited differential responses, suggesting individual recognition by voice. A general description of the species, including their classification, distribution, migration and inter-racial differences, is also given.