Anthropogenic Changes Threaten Eastern Himalayan Birds
Researchers from IISc’s Center for Ecological Sciences (CES) tracked wild bird populations in the Eaglenest Wildlife Sanctuary in Arunachal Pradesh for over a decade. The findings suggest that logging and other disturbances are changing the forest microclimate, making it hotter during the day and colder at night.
These changes stress species that depend on the stable, cool, moist environment of primary forests. The study, conducted between 2011 and 2021, focused on understory insectivorous birds that live and feed under the canopy.
The research team tagged the birds with lightweight aluminum rings and revisited the same sites each year to monitor changes in body mass and survival rates. They also placed temperature and humidity loggers in both intact and selectively recorded forests to understand how microclimatic changes affect bird populations.
“Using these long-term datasets, we can better understand why some species survive after logging, while others decline strongly,” said Akshay Bharadwaj, a former graduate student at CES and corresponding author of the study.
The findings show that in woodland forests where the canopy is thinned or broken, the ground-level environment is more exposed to direct sunlight during the day and loses heat more quickly at night. Such conditions increase stress on thermal specialist birds that have evolved to thrive in the stable, temperate climates typical of intact forests. “Species that can still find microclimates in logged forests similar to their original lodges survive after selective logging. Those that cannot adapt to their former conditions face sharp declines,” Bharadwaj explained. Over time, these birds showed a decrease in body mass and a sharp decline in long-term survival. Researchers warn that such changes could spread throughout the ecosystem. A decrease in insect-eating birds may lead to an increase in the insect population, which may disrupt the ecological balance and affect plant health.
Chestnut-headed Tesia is circled by trained field personnel | Credit: IISc
The team emphasized that conservation efforts should prioritize protecting primary forests at different elevations in the Eastern Himalayas. In areas where forests have already been destroyed, measures such as creating shaded areas or adding water sources to help revitalize microhabitats are recommended.
“Studying these fascinating animals in the field is always exciting. We work in a relatively remote region of Arunachal Pradesh, often under challenging conditions (rain, leeches and elephants), but long-term field data like these are vital. They help us plan practical conservation steps for species facing climate and habitat pressures,” says co-author Umesh Srinivasan, Assistant Professor at CES.
