Call Sonograms And Functions Of Eastern Black Crested Gibbon (Nomasctis Nasutus)

The eastern black crested gibbon (Nomascus nasutus) is a criticallyendangered species with only one small population living in a karst forest alongChina-Vietnam border. Due to the difficult karst terrain, an international border, andsimilarity in male morphology, detailed monitoring of population dynamics and dispersalpatterns are not possible using traditional observation methods. In this study, wemonitored the eastern black crested gibbons in China-Vietnamese border for long time.We analyzed the sonograms of eastern black crested gibbons and compared the duetstructure of eastern black crested gibbon, and tested individuality and stability in malesongs of eastern black crested gibbons, then tested the song functions of eastern blackcrested gibbons.We used a Sony TC-D5Pro2recorder, Sony C-76directed microphoneand Sony tape recorder to record call bouts of three groups of eastern black crestedgibbons from in Bangliang, Guangxi and Vietnam. We got the song bouts of easternblack crested gibbons nearly6years.Call bouts of three groups of eastern black crested gibbons from September2007toJune2009in Bangliang, Guangxi were used and Signal/RTS4.0was used to analyze thesonogram of five high quality bouts for each group. Call frequency of eastern blackcrested gibbon was quite high, sometimes reaching or exceeding5kHz. Adult malesproduced boom, aa notes, pre-modulated note and modulated phrases, whereas adultfemales produced great calls. Adult males and mated females coordinated to producecomplex duets, which usually began with and ended with the male call. We alsocompared the duet structure of eastern black crested gibbon with western black crestedgibbon and Hainan gibbon. Both male and female calls and their coordinated duetsequences showed obvious differences between the three species. Sonogram characters,based on our results, therefore support the division of these groups of Nomascus into thecurrent three species.Call bouts of eastern black crested gibbons from September2007to October2012were used to test individuality and stability in male songs of eastern black crestedgibbons. We then discussed the possibility of using vocal individuality for populationsurveys and monitoring population dynamics and dispersal patterns. Significantindividuality of vocalization was detected in all9males, and the correct rate ofindividual identification yielded by discriminant function analysis using a subset ofvariables was satisfactory (>90%). Vocal stability over2-6years was also documented in4males. During the course of this research, we also observed one male replacement (confirmed by vocal analysis). This time-and labor-saving method might be the mosteffective way to detect dispersal patterns in this transboundary population.We used the singing data of three groups of eastern black crested gibbions fromJanuary2009to December2009to test the three hypotheses of singing function: territorydefense, inter-group spacing and group cohesion.(1) We analyzed the singing sites andthe impact of the conflict to sing behavior, which showed the singing of eastern blackcrested gibbon occurred in the central area of its home range; Inter-group conflict couldstimulate singing behavior, the frequency of female great call would increase. Althoughour results do not support the singing occurred in the border areas, but territory defensehypothesis was partly proved.(2) Neighboring groups did not tend to sing on the sameday. Although they sang on the same day, the phenomenon of song overlapping timeswas more than the number of non-overlapping existed in one of three paired groups. Sowe concluded that a group’s duet could elicit its neighbor to sing.(3) The individualsdecreased distance after the songs and even all day when singing occurred, whichsuggested the song play the group-cohesion function.