Birds in Arunachal Pradesh face dual threat of climate change & deforestation: study

A study in Global Ecology and Conservation used data from bird netting and ringing to see how the bird community in the Eastern Himalayan mid-elevation forests changed in both undisturbed and logged forests. The study found that birds in northeastern India are moving to higher elevations because of rising temperatures from deforestation.

The undisturbed forest was 2.3 degrees Celsius cooler and 14.6% more humid than the logged forest, with fewer arthropods living in the foliage. The researchers noted that larger species, which need more energy, are likely to decrease in number if there are fewer resources.

Tropical montane forests are unique ecosystems that can start at about 150-200 m and reach up to 3,500 m high up on mountains around the world. They are critical centres of biodiversity. “In tropical mountains, each species has a particular niche where it is found. This restriction creates much more diversity in a small space,” explains Ritobroto Chanda, former Project Associate at the Centre for Ecological Sciences (CES), IISc, and corresponding author of the study.

The researchers studied a montane broadleaved forest in the Eaglenest Wildlife Sanctuary in Arunachal Pradesh in the Eastern Himalayas. From 2011 to 2021, they captured 6,189 birds from 130 species. The final analysis included 4,801 insect-eating birds that live under the canopy of large trees, belonging to about 61 species, said Umesh Srinivasan, an assistant professor at CES and co-author of the study.

The authors of the research noted that while many studies have looked at the separate impacts of habitat loss and climate change on biodiversity, few have looked at the influence of both these threats together, especially in the tropics and particularly in tropical mountains.

Logging impacts bird diversity negatively

The loss of forests and climate change are big threats to ecosystems. A bird called the yellow-throated fulvetta, along with many other plants and animals in tropical mountain ranges, are very sensitive to temperature. They’re quickly reacting to global warming. Also, most of the world’s land-based biodiversity is found in tropical mountains, says Umesh Srinivasan, an Assistant Professor at CES.

The research team found that many bird species are moving to higher places because of increasing temperatures. Logged forests are warmer and less humid than untouched forests, which speeds up this movement. Smaller birds seem to handle the higher temperatures in logged forests better, while larger bird species are becoming more common in untouched forests.

Insect-eating birds decline in numbers

The team gathered data from the Eaglenest Wildlife Sanctuary in Arunachal Pradesh, a biodiversity hotspot in the Eastern Himalayas that’s home to over 500 bird species. Loggers heavily logged the area until 2002, and the logged areas differ greatly from the untouched forests, which makes them suitable for study.

Every day, after setting up nets to catch birds, the team checked them every 20-30 minutes. They weighed and tagged the birds, then let them go right away. Out of the 6,189 birds they caught from 130 species, the final analysis included 4,801 insect-eating birds that live under the canopy of large trees, from about 61 species.

The team concluded that logging could cause the loss of large, old, growth-dependent species and decrease overall biodiversity. They also discovered that logging along with the availability of specific locations negatively impacts insect-eating birds. These birds usually inhabit specific places and are experiencing a sharp decline in their numbers.

Logged forests also have fewer insects living in the foliage, which means less food for the birds. Since larger species need more energy, this reduces the number of large species even more.

According to the researchers, the study highlights the need to safeguard primary forests in order to mitigate the effects of climate change.

Srinivasan said, “Logging managers should ensure to protect undisturbed forests across large elevational gradients.” He explained that this protection would allow species to shift their ranges upwards in response to climate change and maintain survival. “If species encounter degraded forest while shifting upwards, the chances of certain species going locally extinct are high.”

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