Human pressure forces endangered macaques to alter behavior: study

A new study by the Bengaluru-based Centre for Wildlife Studies (CWS) has found how the endangered and endemic lion-tailed macaque (Macaca silenus) uses its habitat selectively and strategically in response to increasing human pressure.

The study, conducted in Silent Valley National Park and titled "The Fluctuations of Tree Life: Space Use and Movement Strategies of Lion-Tailed Macaques (Macaca silenus) in the Western Ghats of India", highlights how differences in forest management and human presence can influence animal behaviour even in protected areas with similar forest compositions.

The lion-tailed macaque is found only in the Western Ghats, with fewer than 4,000 individuals remaining and the Silent Valley National Park is a stronghold for its conservation.

The IUCN (International Union for Conservation of Nature) lists the lion-tailed macaque as "Endangered". This designation reflects the species' declining population due to significant habitat loss, primarily from deforestation for agriculture and development. The lion-tailed macaque is endemic to the Western Ghats region of India, specifically in Karnataka, Kerala, and Tamil Nadu.

Sikha Hariharan, a doctoral fellow at CWS, led the study. She examined the spatial ecology and movement-based habitat selection of two lion-tailed macaque groups living in areas with different levels of human presence within the park boundaries.

CWS scientists monitored two groups of macaques, one in the boundary or buffer zone and the other in the core area of ​​the national park.

They combined GPS tracking, vertical space use estimation, and advanced activity modeling to study how macaques use the space around them, whether above the forest canopy or on the forest floor, with one in the edge or buffer zone and the other in the core area.

The study group living in the buffer of the protected area maintained a small home range and spent almost all of its time (94.2%) in the mid-level forest canopy, the CWS said.

"Their avoidance of the lowest forest area indicates a strategic response to ecological factors and increased risks from humans, hunters or other disturbances. In contrast, interior troops showed greater use of the forest floor, with larger contingents landing on the ground and occupying much larger home ranges," the CWS said.

Ecological resilience

The findings show that while both groups mostly stay in the middle part of the forest canopy, the group living deeper in the forest spends more time on the ground. This ground-based behaviour suggests that the species may be more adaptable than previously thought, as it was long believed to live only on trees. The macaques also tended to spend more time near important resources, such as fruiting trees and areas with thick canopies.

Hariharan noted that an animal’s activity reflects its perception of the environment and how it negotiates trade-offs between food acquisition, safety, and survival. It often serves as the first visible sign of how a species is responding to environmental changes.

"Earlier, macaques were thought to come to the ground only in damaged or disturbed habitats. But our study shows that even in undisturbed forests, they regularly explore and use the forest floor," said Hariharan. "However, being on the ground can expose them to more risks. That’s why it’s important for them to stay connected to the canopy. It’s also crucial to include their use of vertical space when planning for wildlife conservation."

Edited by Diwash Gahatraj

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