Spectral characteristics and sex differences in the song of Skywalker hoolock gibbon(Hoolock tianxing)
Species of the genus Hoolock were previously thought to lack sexual dimorphism.Identifying sexual dimor-phism in vocalizations is helpful for their population dynamics monitoring and behavioral research.In this study,we an-notate the song bouts of 11 Hoolock tianxing individuals.We employed k-medoids clustering to divide note types,and we classified phrase types based on the length and note composition of phrases.We also compared sexual dimorphism in notes and phrases.We identified 5 note types:wa,oo,whoop,ow and eek.The range and rate of frequency modulation of wa and ow notes of females were higher than those of males,the frequency features of oo notes were lower than those of males,the range and rate of frequency modulation of whoop notes were lower than those of males.For the phrases use,solitary apes were more similar to the parts contributed by their respective genders during a chorus.Males seldom sing phrase G mainly composed of the whoop note and the ow note,females seldom sing phrase B(wa-whoop)and phrase C(wa-oo-wa-whoop).Our study demonstrated sexual dimorphism in the vocalizations of Hoolock tianxing,which is not only helpful for the monitoring of Hoolock tianxing,but also important for understanding the function of dif-ferent note types and sex differences.