When there is no forest left: fragmentation, local extinction, and small population sizes in the Sri Lankan western purple-faced langur

Abstract

The western purple-faced langur Trachypithecus vetulus nestor is a Critically Endangered primate endemic to Sri Lanka according to the International Union for Conservation of Nature (IUCN). Its population decline is inferred mainly due to vast habitat loss. Few recent data are available regarding its distribution or abundance. The aim of our study was to assess the conservation status of T. v. nestor throughout its known historical range by establishing presence/absence and correlating these data with semi-structured interviews determining human perceptions and threats. Twenty-six sites were investigated, with presence of T. v. nestor being confirmed at 11 and indicated through questionnaires only at 2 additional sites. The present distribution of T. v. nestor is severely fragmented both locally and regionally. More than half of the populations comprised 1 or 2 groups only and, being isolated in a matrix of urban landscapes, are close to unviable. Conflicts between local people and T. v. nestor were identified at such sites, where reports of troops crop-raiding gardens and plantations were associated with negative perceptions. Consequences for crop-raiding langurs ranged from shouting to (infrequently) shooting and killing by dogs. Negative views towards T. v. nestor were significantly related to the length of time they spent in anthropogenic landscapes, while more positive views were significantly associated with the length of time T. v. nestor spent in forested areas. Evidence of local extinctions means that the remaining, yet increasingly fragmented habitat of the highly arboreal T. v. nestor is critical for survival. Intervention to manage this human-wildlife conflict is vital. An integrated approach using international and local conservation authorities is highly recommended.

Habitat use and Documentation of a Historic Decline of Western Hoolock Gibbon (Hoolock hoolock) in Dampa Tiger Reserve, Mizoram, India

“…Soliciting information from villagers can lead to a better understanding of the attitudes and perceptions of people towards biodiversity conservation including complex issues researchers may miss when conducting an ecological study. When interpreted with care, interview data can provide good insights regarding the (local) status of threatened primates (Parker et al 2008;Meijaard et al 2011). Our approach was a general one, without giving precise time periods but referring to key events (civil unrest, establishment of the area as a Tiger Reserve) instead.…”

Purple-faced Langurs in Human-Modified Environments Feeding on Cultivated Fruits: A Comment to Dela (2007, 2012)

“…Between 81 % and 90 % of the natural habitat in the range of the western purple-faced langur has been replaced by residential areas, home gardens, plantations, and other human-dominated areas (Rudran 2008;Rudran et al 2009). Within this region it appears to be absent from approximately half of the sites where it was known historically, and remaining populations are isolated by kilometers of unsuitable habitat (Parker et al 2008). Rudran et al (2009: p. 53) concluded that "deforestation has fragmented and drastically depleted the preferred habitat and principal food sources of the highly arboreal and folivorous T. v.…”

“…The researchers showed that infection with the apicomplexan protozoan Cryptosporidium (causing the diarrheal illness cryptosporidiosis in humans) was higher in purple-faced langur groups using areas and water that had been heavily soiled by human feces and livestock (Ekanayake et al 2006). Work in the more urbanized parts of the purplefaced langur's range highlighted some of the other dangers of living too close to humans, with langurs being killed by electrocution and guard dogs, or by traffic while crossing roads (De Silva et al 2011;Parker et al 2008).…”

“…Dela's research demonstrated the behavioral plasticity of the purple-faced langurs allowing them to survive in human-modified environments. It also illustrated the extreme situation the purple-faced langurs face, especially in western Sri Lanka, with hardly any forest left and purple-faced langurs living almost exclusively commensally with humans (Parker et al 2008); indeed in the years after Dela's study, her study groups lost large proportions of the trees in their home ranges because of clear-felling (Dela 2012).…”

“…In the 2000s researchers conducted a number of surveys to assess the distribution and status of purple-faced langurs (Bernede 2003;De Silva et al 2011;Nahallage et al 2008;Parker et al 2008;Peiman 2001;Rudran 2008), especially in the western part of their range, leading to the species being considered globally Endangered according to IUCN threat criteria (Dittus et al 2008). Between 81 % and 90 % of the natural habitat in the range of the western purple-faced langur has been replaced by residential areas, home gardens, plantations, and other human-dominated areas (Rudran 2008;Rudran et al 2009).…”