Silky sifaka (Propithecus candidus) “zzuss” vocalizations: Sexual dimorphism, individuality, and function in the alarm call of a monomorphic lemur

Abstract

Vocalizations of Madagascar's lemurs have generally been less investigated than those of other primate groups, with virtually no information available about calling in the silky sifaka (Propithecus candidus), a large rainforest species. Current work examined the "zzuss" vocalization, one of the most common and loudest sounds produced by this monomorphic species, and included 160 calls from nine adults (five males, four females) in three groups. Analyses focused on overall acoustic features, individual and sex differences, call usage, and likely function. Acoustically, the calls included separable turbulent noise and tonal components, with the later often marked by frequency jumps and dramatic frequency modulation. Male and female zzuss calls differed most in F0- and amplitude-related features, characteristics that are relatively unconstrained by overall body size. All measures differed among individual callers, with F0-related variables again playing the largest role. Based on usage, these calls most likely function both as generalized alarm and group-coordination signals. The sounds were thus of interest in several regards, including showing sexual differentiation in the absence of other dimorphisms, exhibiting primarily F0-based differentiation in both sex- and individual-based comparisons, and combining apparent alarm and coordination functions across a variety of contexts.