BENGALURU: Researchers at the IISc studied the effects of forest logging and climate change on bird species in tropical mountains by examining over 10 years of data.
The team used mist netting and bird ringing data to answer how the composition of the mid-elevation Eastern Himalayan understorey bird community changed in undisturbed forests and wood-cutting forests.
Tropical montane forests are unique ecosystems that can start at around 200 metres and reach up to 3,500 metres high up on mountains around the world.
They are critical centres of biodiversity. Forest loss and climate change present major threats to these ecosystems. “Birds and much of the flora and fauna of tropical mountain ranges are extremely temperature-sensitive and are responding to global heating rapidly. Also, most of the world’s terrestrial biodiversity is concentrated in tropical mountains,” said Umesh Srinivasan, assistant professor, Centre for Ecological Sciences (CES), IISc, and corresponding author of the study.
The report published in Global Ecology and Conservation collected data from the Eaglenest Wildlife Sanctuary, Arunachal Pradesh, situated in the biodiversity hotspot of Eastern Himalayas and home to over 500 bird species. The area saw intensive logging until 2002. The study highlighted that many bird species have started shifting to higher elevations due to rising temperatures.
Logged forests have higher average temperatures and lower humidity than primary forests, which is hastening the transition. Birds that are smaller in size are colonising these logged forests better because they can tolerate higher temperatures, while the density of larger bird species appears to be increasing in the untouched forests.
Every day after setting up the mist nets, the team checked them every 20-30 minutes, weighed and labelled the birds, and released them immediately. “Of the 6,189 captured individuals from 130 species, the final analysis included 4,801 understorey insect-eating birds that live under the canopy of large trees – belonging to about 61 species,” the researchers said. They focused on these birds because their niches are well defined and abundant data from the mist nets is available for them.
The study showed that logging can lead to the loss of large-bodied, old growth-dependent species, and decrease the overall biodiversity.