Chestnut-headed tesia are circled by trained field workers. | Photo credit: SPECIAL ARRANGEMENT
A new study from the Indian Institute of Science (IISc) has revealed that insectivorous birds found in the undergrowth of the eastern Himalayas are threatened by habitat degradation.
Scientists from the Center for Ecological Sciences (CES) studied how changes in forest microclimate following selective logging affect the survival of wild bird populations in the Eaglenest Wildlife Sanctuary, Arunachal Pradesh, over a 10-year period between 2011 and 2021.
The team marked the birds with lightweight aluminum rings and revisited the same locations each year to track their survival and changes in body weight.
Matching datasets
IISc said the team paired this data set with temperature and humidity loggers located in both primary and logged forests to estimate how understory insectivorous birds that live under the canopy are adapting to microclimate changes.
“Using these long-term data sets, we can better understand why some species survive after logging while others decline sharply,” said Akshay Bharadwaj, former CES Master of Science student and corresponding author of the study.
Overall, the team found that logged forests are consistently warmer and drier during the day and cooler at night compared to primary forests, exposing the birds to stressful fluctuations due to the loss of the forest canopy.
Impact of climate change
These conditions, the researchers say, could intensify with climate change, especially in the eastern Himalayas, where bird species are heat specialists.
Their findings reveal that these birds, which use very different primary and logged forest microclimatic niches, are most adversely affected in logged forests, experiencing reduced body weight and steep declines in long-term survival.
“Species that can still find microclimates in cleared forests similar to their original forest homes survive after selective logging. It is those that cannot match their old conditions that face steep declines,” Mr Bharadwaj said.
Based on their findings, the researchers suggest that conservation strategies should prioritize the preservation of primary forest across altitudinal gradients.
The study highlights the importance of understanding why certain bird species decline after mining and how microclimatic niches in disturbed habitats affect population dynamics.
Long-term database
“Long-term data sets are key to this, and we continue to collect these data to try to plan effective conservation measures for these bird species. As the climate warms, the persistence of microhabitats will be key for many species to remain resilient to climate impacts,” said Umesh Srinivasan, assistant professor at CES and co-author of the study.
Published – 12 Nov 2025 22:08 IST
