The structure of vocalization of ewes and male lambs at pasture.

We performed an analysis of the vocalization of 161 ewes and 50 male lambs that were pastured day and night. The vocalization structures of the phonetic notations of the opened-mouth from closed mouth /etaaee/ and /etanaeee/ and closed-mouth /etaetaetaeta/ of ewes, and the opened-mouth from closed-mouth /etaeee/ and /etaneeee/ and closed-mouth /etaetaetaeta/ of male lambs were studied in terms of their audio characteristics. The items subject to analysis included duration of each vocalization, fundamental frequency, sound pressure and first formant (F1), second formant (F2), and third formant (F3). Among the male lambs, the duration of each call type showed significant differences depending on the behavior types or the target types, and the closed-mouth to open-mouth sounds, /etaeee/ and /etaneeee/ showed a tendency to be longer than the closed-mouth sound of /etaetaetaeta/. A significant correlation (r = 0.9, P < 0.05) was observed between the fundamental frequency and F1 with the /etaeee/ type of call of the male lambs when the vocalization was targeted toward the stockperson. When the ewes' behavior pattern was grazing and moving and the calling target was an ewe, the sound pressure significantly differed between /etaetaetaeta/ and /etanaeee/ (P < 0.05). From the analysis of the call durations, the fundamental frequencies, the sound pressures and formants, and the particular characteristics in sound structure were shown to vary according to the vocalization conditions and the situations, and where the animals were placed, even within the same call types.