[Sonogram structure and timing of duets of western black crested gibbon in Wuliang Mountain].

We studied the sonogram and timing of duets of three groups of Central Yunnan western black crested gibbons (Nomascus concolor jingdongensis) in Dazhaizi, Mt. Wuliang. The study was based on a 13-month field observation period, from March 2003 to March 2004. A Sony TC-D5 Pro2 recorder, Sony C-76 directed microphone, and Sony tape were used to record the duet bouts in March 2007 and March 2008. Signal/RTS 4.0 was used to analyze the sonogram of the duet. We first presented sonograms of all kinds of sound units in the duets made by western black crested gibbons. The adult male could produce boom, aa notes and modulated figures. Adult females produced great call or abortive great call. The two adult females in each group usually produced great calls synchronously. After the great call, males always immediately produced a modulated figure to coordinate with the female. The interval between the modulated figure and great call was 2.7 s. On average, groups sang on 53% of days monitored, and sang 1.09 duet bouts per singing day. 91.5% of the duets were produced between half an hour before and three hours after the sunrise. The average duration of the duets was 12.9 min, and females produced 4.6 great calls during one duet bout. The intervals between two successive great calls were generally 115 s. There was no significant difference in the duration and frequency of the duet bouts, but there was significant difference in the number of the great calls and intervals between great calls among groups.