Colonial-era land-use changes in India led to severe decline in grassland birds, study finds

(Press-News.org) Ithaca, NY—A new study published in the journal Global Change Biology reveals that colonial-era landscape modifications have resulted in a devastating 80% loss of grassland habitat and significant declines in grassland bird populations in India's Nilgiri hills over the past 170 years.

An international research team—led by scientists from Columbia University, the K. Lisa Yang Center for Conservation Bioacoustics at the Cornell Lab of Ornithology, Indian Institute of Science Education and Research Tirupati, and 10 other institutions—analyzed an extensive dataset comparing historical land cover maps from 1848 with modern satellite imagery and bird observations from 1850 to 2021.

“What's unique about this work,” said Vijay Ramesh, lead author and postdoctoral fellow at the Cornell Lab of Ornithology, “is that we contrasted historical datasets from two centuries ago with present-day data collected from the field. We show that maps, hunting records, and museum specimens can be leveraged to estimate baseline environmental conditions against which data from modern ecological surveys and satellite imagery can be compared.”

The research team found that about 90% of grassland birds have significantly declined in relative abundance since the 1850s. Eight out of the nine grassland bird species the research team studied showed significant population declines. Birds such as the Nilgiri Pipit and the Malabar Lark showed the steepest declines over time. According to the study, this decline coincides with colonial-era policies that favored converting natural grasslands into tea and timber plantations. 

"British settlers viewed grasslands as wastelands, and this notion has resulted in the large-scale plantations of tea, and exotic timber species (such as acacia, eucalyptus, and pine) that we see today in this highly biodiverse region,” said Ramesh. 

Somewhat surprisingly, the authors found that 53% of the forest birds they studied have not declined as dramatically over the past two centuries. “Some forest birds in the Nilgiri hills seem to be using timber plantations despite the fact that these monocultures do not offer the complex habitat structure that native forests are able to provide," said Ramesh. But the authors stress that this result is specific to the historical context in India and does not provide evidence that plantations are suitable replacements for all forest birds. 

Unlike some forest birds that moved into timber plantations, for grassland birds little alternative habitat exists in the region. “We are losing grasslands at a rapid rate today, which has resulted in cascading effects on fauna that depend on these unique habitats. While forest conservation certainly requires continued attention, we hope that our work urges policymakers to also prioritize grassland protection and restoration equally. The key message we want readers to take away is that open natural ecosystems such as grasslands are undervalued hotspots of biological diversity,” said Ramesh.

The results of the study are now available to the public and Ramesh hopes that conservation practitioners and State Forest Departments in India can assess which areas have undergone conversion from grassland to plantations, and where restoration efforts should be focused.

This research was made possible by the contributions of numerous scientists including Priyanka Hariharan at the University of Florida; Pratik Rajan Gupte at the University of Groningen; Ashwini Mohan at the Natural History Museum London and the University of Neuchatel;  VA Akshay at University of Florida; Amrutha Rajan at Indian Institute of Science Education and Research Tirupati; Chandrasekar Das at the Keystone Foundation; Ian Lockwood at Overseas School of Colombo; VV Robin at Indian Institute of Science Education and Research Tirupati; Morgan Tingley at University of California, Los Angeles; and Ruth DeFries at Columbia University.

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