Calling patterns of Western purple-faced langurs (Mammalia: Primates: Cercopithecidea: Trachypithecus vetulus nestor) in a degraded human landscape in Sri Lanka

Abstract

The study of calling patterns is a useful non-invasive method for determining population densities and the taxonomic relationships of rare or cryptic animal species. The Western purple-faced langur Trachypithecus vetulus nestor, endemic to Sri Lanka’s lowland rainforests, is severely impacted by forest fragmentation, with most remaining populations living almost completely in home gardens. Due to their shy nature, little is known about the behaviour of this subspecies; analysing the regular loud calls emitted by these langurs could allow for improvement of census techniques, clarification of their taxonomy, and an understanding of the impact of forest destruction on their behaviour. In 2007, we recorded the calling patterns of five male T. v. nestor at Talangama Wetlands. Time, duration, weather conditions, and stimulant of 253 calls were noted. Loud calls comprised three structural units: harsh barks, whoops and residuals. The average call contained 4 phrases and 3.8 residuals, was 38 seconds in length, had an average maximum frequency of 3.5 kHz, a formant frequency of 0.36 kHz, and a fundamental frequency of 0.2 kHz. Significant differences were found between individuals for the number of phrases and residuals within a call, two different phrase lengths, the formant frequency and the fundamental frequency. The earliest call occurred at 05:27 hrs, while the latest was made at 17:57 hrs. The greatest percentage of calls (73.5%) was heard in the morning (05:00-09:59 hrs), mostly stimulated by territorial battles with neighbouring troops. These results show that vocalisations can be used to distinguish individual males; as langurs are more often heard than seen, and most troops contain only a single adult male, vocalisations may be used to determine the number of troops in an area. Calls of this taxon also differed from the other subspecies, suggesting that they may be used to distinguish subspecies and their boundaries. Finally, calling behaviour differed from other subspecies. Deforestation may be a direct cause of different calling patterns. These baseline data form a valuable starting point for further studies of this Critically Endangered primate.

A New Color Morph of the Southern Purple-faced Langur (Semnopithecus vetulus vetulus) from the Rainforests of Southwestern Sri Lanka

“…Semnopithecus v. vetulus is likely to habituate further (Eschmann 2008), but occurrences such as the shooting we recorded and that of Dela (2004) should stop if the whole community is aware of the consequences. Education of the younger generation is possible through schemes such as 'Trees for monkeys' by the Wildlife Conservation Sociendemic Artocarpus nobilis tree (Moraceae).…”

Vocal acoustics in the endangered proboscis monkey (Nasalis larvatus)

“…With the development of new bioacoustic technologies, bioacoustic monitoring became an interesting issue for conservation‐related activities [Blumstein et al, ; Eschmann et al, ; Laiolo, ; Marques et al, ; Obrist et al, ]. Multiple microphone arrays linked to long‐term automatic recording devices can be installed in the environment and specified analysis software (e.g., pattern recognition via trained neural networks) can extract information on biodiversity, abundance of species, and distribution of species in the habitat.…”

Habitat use by western purple-faced langurs Trachypithecus vetulus nestor (Colobinae) in a fragmented suburban landscape

“…Buddhist beliefs have, in the past, shielded T. v. nestor to some extent from persecution (Rudran 2007, Wolfe & Fuentes 2007, but recent reports in Sri Lanka suggest a shift in human tolerance (Dela 2004, Nahallage et al 2008. This shift may be exacerbated by the fact that T. v. nestor is showing greater tolerance towards humans, thus making individuals of the species easy targets for catapults and rifles (Eschmann et al 2008). It is evident that a broader understanding of the complex interactions that take place between humans and primates living in sympatry is of paramount importance to the survival of T. v. nestor.…”