Montane bird communities are transformed by logging and climate

The Indian Institute of Science (IISc) has released a compelling report on the impact of logging and climate change on bird communities in tropical montane forests. 

The researchers analyzed more than a decade of data, focusing on bird communities in the Eastern Himalayas’ mid-elevation understory. 

The team used methods like mist netting to explore changes in montane bird communities in both primary (undisturbed) and logged forests.

Tropical montane forests

Tropical montane forests, ranging from 150-200 meters to 3,500 meters in altitude, are biodiversity hotspots. 

“In tropical mountains, each species has a particular niche where it is found. This restriction creates much more diversity in a small space,” explained Ritobroto Chanda, a former project associate at the Centre for Ecological Sciences (CES).

Significant threats 

Tropical mountain ecosystems face significant threats from forest loss and climate change, yet very few studies have explored these impacts. 

“Birds – and indeed 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,” noted Professor Umesh Srinivasan. He emphasized the need to investigate the combined impact of these threats.

Key findings

The IISc team observed many bird species shifting to higher elevations due to rising temperatures. In logged forests, higher temperatures and lower humidity accelerated this transition. 

Interestingly, smaller montane birds adapted better to logged forests, while larger species density increased in primary forests.

Eaglenest Wildlife Sanctuary

The study was conducted in the Eaglenest Wildlife Sanctuary in Arunachal Pradesh, a region known for its rich avian diversity, hosting over 500 bird species. 

The area’s history of intensive logging (until 2002) offered a distinct contrast between logged and intact forests, making it an ideal site for this study.

Local support

Chanda noted that the support of the local community is critical to carry out such research. “You have to stay in a wildlife sanctuary with no paved roads, no electricity, and no place to stay as such.”

“We take our food with us, cook on a daily basis, make a makeshift camp and move around, and without the people’s support, it’s really not possible to continue this for a long time,” said Chanda.

How the research was conducted 

The researchers’ daily routine involved setting up mist nets, checking them every 20-30 minutes, processing the birds, and releasing them. Out of 6,189 captured individuals from 130 species, the study focused on 4,801 understory insectivores from about 61 species.

The researchers focused on these particular montane birds because their niches are well defined and abundant data is available for them. The study did not include rare species that may skew the results. 

Impact of logging 

The analysis revealed that logging leads to the loss of large-bodied, old-growth-dependent species, and a decrease in overall biodiversity. 

Logging negatively impacts understory insectivores, leading to a significant decline in their numbers. Furthermore, logged forests have lower insect densities, affecting the birds’ food resources.

Study implications 

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

“Logging managers should ensure that undisturbed forests across large elevational gradients are protected,” said Srinivasan. He explained that this will allow species to shift their ranges upwards in response to climate change and maintain survival. “If species encounter degraded forest while they shift upwards, certain species will most likely go locally extinct.” 

The study is published in the journal Global Ecology and Conservation. 

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