Science Feature

Migratory birds make a pit stop at mine lakes

Open-pit mining in eastern India has carved out unique yet neglected water havens that must be conserved.

Richa Malhotra

doi:10.1038/nindia.2020.121 Published online 13 August 2020

 A cotton teal swims in a pit lake in eastern India.

© Santanu Gupta

Every winter, migratory birds descend upon the Indian sub-continent from far-off lands in search of warmer climes. During these long flights, the birds stop by wetlands to rest and refuel. Scores of ‘pit lakes’, formed as a result of open-pit mining in West Bengal and Jharkhand, offer the avian guests a stopover venue, new research suggests1.

The rich habitat of these pit lakes also attracts a number of local bird species, and therefore it is important to conserve them, according to researchers from the Salim Ali Centre for Ornithology and Natural History (SACON) in Coimbatore, Tamil Nadu.

Pit lakes are formed when groundwater and rains fill up mining dug-outs. New pit lakes may have poor water quality but with time a few of them develop into healthy ecosystems, harbouring wildlife and supporting local communities.

A pit lake habitat naturally restored over several years in the mining belt of West Bengal looks lush green during the monsoon.

© Santanu Gupta

SACON’s Santanu Gupta prepared an inventory of 62 such pit lakes in the Eastern Coalfields Limited’s (ECL) mining operations in West Bengal and Jharkhand. Some of these lakes are more than 50 years old2. Using a combination of mathematical models and field visits, Gupta and colleagues assessed 20 lakes to see how suitable they are for birds. They found three pit lakes to be highly favourable for the species they chose to study – the long-distance migrants bar-headed goose and red-crested pochard; and the locally dispersing cotton teal (also called pygmy-goose).

The researchers mapped the three pit lakes and divided each into three conservation zones – a  ‘conservation priority site’ with the restored lake at its core; a ‘habitat development zone’ where trees have been planted; and an ‘eco-overlap zone’ criss-crossed by farms, homes and roads.

The priority site of the lakes can be protected as they are, says Snehangshu Das, a Master’s student at Shivaji University in Maharashtra and co-author of the study. In the habitat development zone, non-indigenous trees planted by ECL to rehabilitate the land will need to be replaced by indigenous varieties, Das says. All human activities, he adds, should be restricted to the eco-overlap zone.

During their survey of the 20 pit lakes, the researchers counted 41 resident and 10 migratory bird species. They also found nests of some resident bird species.

However, despite being important bird habitats and a source of water for communities, pit lakes find no mention in state or national wetland policies such as the West Bengal Wetlands and Water Bodies Conservation Policy or the National Plan for Conservation of Aquatic Eco-systems.

These unrecognised lakes also face the threats of pollution and infilling. According to Gupta, at least five pit lakes have been entirely or partially filled with either coal ash waste from thermal power plants or debris from active coal mines nearby. The flattened land is repurposed for human housing and other development activities, Gupta says.

Gupta and team hold ECL, a subsidiary of the government-owned Coal India Limited, accountable for not fulfilling their corporate social responsibility (CSR). During 2017-18, the company spent3 most of its CSR funds on activities unrelated to the environment while a balance of Rs 15.52 crore from the allocations remained unspent. ECL must take responsibility in protecting the biodiversity of the pit lakes, the researchers say.


1. Das, S. et al. Spatial prioritization of selected mining pitlakes from Eastern Coalfields region, India: A species distribution modelling approach, Conserv. Sci. Practice (2020) doi: 10.1111/csp2.216

2. Gupta, S. Ecological exploration and socioeconomic valuation of pitlakes in Eastern Coalfields, India: Implications for conservation and sustainable use. Annual Progress Report (1). Submitted to DST, GoI (2018)

3. ECL Annual Report 2017-18, 64-72 (2018) Report