Guwahati: Have you seen capped langurs drinking water from a tree hole?
Arboreal species rarely descend to the ground because of its associated predation risks, which far outweigh the reward in return.
A unique drinking behaviour of capped langur from tree holes was noticed by scientists from Hollongapar Gibbon in Assam in 2015 which has now been published in Current Science journal.
The behaviour was noticed by Samrat Sengupta of the Department of Zoology, Debraj Roy College, Golaghat and Narayan Sharma of the Department of Environmental Biology and Wildlife Sciences, Cotton University.
“Drinking behaviour in primates, though less reported, holds critical insights into conservation planning and management of their habitat. However, this behaviour has been reported only from certain primate species and populations, especially the New-World Primates, with anecdotal notes from the Old-World Primate group. In this context, our observation could very well be the first published record of ingestion of water from a tree hole by a free-ranging troop of capped langur and, thus, provides valuable insight into the physiological requirements of a typical folivore in general, whose diet primarily comprises of leaves, both young and mature” Samrat Sengupta of Debraj Roy College told EastMojo.
The Hollongapar Gibbon Sanctuary (HGS) is a small forest patch of 20.98 sq km in the Upper Brahmaputra Valley, known worldwide for its rich assemblage of the arboreal mammal community.
The arboreal mammal community of HGS has been studied extensively over the last few decades. Only one study reported sporadic observations of drinking behaviour from the water accumulated in tree holes among two of the six primate species in the Sanctuary. These observations involved a typical ‘dipping-and licking’ behaviour by adult individuals of western hoolock gibbon Hoolock hoolock and northern pig-tailed macaque Macaca leonina. However, no capped langurs have ever been observed to drink water directly from any such standing sources.
The study says a troop of capped langurs was spotted foraging near the Forest Inspection Bungalow. Drinking behaviour was observed in one adult male from the water-filled hole of a Ficus ben ghalensis tree. While drinking from the tree hole, the individual first positioned himself comfortably near the height at which the tree hole was located and then inserted his head to drink the water accumulated in it. Apart from this single event, feeding observation on some aquatic plants in a nearby standing pool, for which the troop had to cross an intervening railway track, was also documented. Surprisingly, no drinking behaviour was observed during this instance despite being knee-deep in water in the pool.
“In the case of folivores such as capped langur, a dietary change to mature leaves can also induce supplemental drinking behaviour, to maintain hydration owing to the high non-digestible fibre and secondary compounds intake which puts additional water stress for efficient detoxification. Interestingly, the present study recorded these observations when the group was still feeding on young leaves,” Samrat said.
The study quoting the scientists believe that primates’ drinking water from tree holes may largely be context-specific behaviour, which they seldom resort to, depending on specific local conditions (water availability) and the diet they select.
Scientists say climate change and habitat degradation are likely to impose new unseen challenges for the continued survival of arboreal inhabitants, especially in the tropics with distinct seasonality of weather patterns. “Food resources, being patchy and distributed unpredictably over space and time, will play a crucial role. Animals who are flexible enough to incorporate the required changes in their diet, including their water budget, will have a better chance of survival. However, for this to materialize, water-filled tree holes should be an important resource element in all existing forest management plans, as they are known to provide critical habitats for many organisms and a source of free water during water-stress conditions.
“Water-filled tree holes should be an important resource element in all existing forest management plans, as they are known to provide critical habitats for many organisms and a source of free water during water stress situations,” Samrat Sengupta says.
The scientists urged field biologists to adopt continuous, unhindered data collection with a finer temporal resolution of sampling, especially during the rainy season, to increase the chances of documenting such relatively rare behaviour, which goes unreported because of short-term studies largely avoiding rainy season. “This will also help understand folivore ecology concerning their diet and the concomitant water requirement,” they said.
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