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Thursday, October 21, 2021

Migratory bird numbers down in Bengaluru, finds survey

Lake restoration has positive effect on resident bird figures

By: Express News Service | Bengaluru |
Updated: October 12, 2021 3:39:14 pm
The study also found that larger lakes support more bird species | Express photo

A recent paper titled “Relationship between lake area and distance from the city center on lake dependent resident and migratory birds in urban Bengaluru, a tropical mega-city in Southern India” has highlighted the impact of urbanization on birds.

The study published in the Journal of Urban Ecology has found that the size of the lake area and its distance from the city center are correlated to the number of bird species that frequent the lake. Larger lakes support more bird species. As the distance from the city center increased, the number of bird species increased.

Authored by Ravi Jambhekar, Kulbhushansingh Suryawanshi and Harini Nagendra, the paper investigated how the number of bird species found in Bengaluru’s lakes is related to the size of the degree of urbanization in surrounding areas.

Ravi Jambhekar, Visiting Scientist, Center for Ecological Sciences, Indian Institute of Science, spoke about the changing bird populations in Bengaluru. “We explored the populations of waterbirds in and around the city of Bangalore. Our study found that migratory birds visiting the city are declining but resident bird populations are increasing. We speculate that the decline behind migratory bird populations might be because of some changes happening in the breeding grounds but lake restoration, creation of islands in the lakes are helping resident birds. More species-level studies are required to understand the mechanisms behind these patterns,” he said.

The study used data from eBird, an online database where citizens, researchers and bird enthusiasts upload their bird observations. Overall, migratory bird numbers are declining in Bengaluru, while many lake-dependent resident bird numbers seem to be increasing in the past five years. These declines in migrant species are likely to be associated with conditions on the breeding grounds rather than on the wintering grounds in the city.

“Larger lakes support more diversity as compared to smaller lakes. Larger lakes are likely to have more resting and breeding spaces, feeding resources, and microhabitats required for birds. Lakes in the center of the city have less bird diversity as compared to lakes on the outskirts. This might be because of better habitat conditions, better breeding and feeding opportunities in the lakes outside the city,” the study says.

Harini Nagendra of Azim Premji University said, “Bengaluru’s lakes have a chequered past, having gone through multiple phases of creation, renewal, loss, and restoration. These changes have impacted bird diversity, ultimately affecting the character and beauty of Bengaluru – the city of lakes. Our exploration of eBird data exploits the power of citizen science to understand how bird communities have changed over time in response to the growth of the city and the restoration of lakes. Such research is important to manage lakes and wetlands for biodiversity.”

Birds that nest in tree canopies such as cormorants, painted stork, brahminy kite, and egrets are increasing. The study observed that this might be because of the availability of nesting sites in the islands created by the authorities. Many of these species are also piscivores (fish-eaters) and another reason for their increase could be the increase in the number of fish in the lakes, the main prey of these birds.

“Nine of the ten duck species found in the city of Bengaluru are declining. These declines are being reflected in the migratory sites. The decline in duck populations might be associated with urban pressure on their breeding grounds (perhaps from feral dogs and cats or other unknown forms of stress). Fish-eating birds such as cormorants, oriental darter are increasing in the city. Rejuvenating lakes in terms of desilting, creating islands, and introducing fish stocks to these lakes might increase food availability in the lakes, helping these birds maintain stable populations in cities,” an excerpt from the study read.

Kulbhushan Singh Suryawanshi, Scientist, Nature Conservation Foundation (NCF), spoke about the declining numbers of species like the pied kingfisher and how it can be avoided. “With proper management, lakes of Bengaluru have great potential for conservation of birds within the mega city. While bird watching around Bengaluru’s lakes, we have seen many species of waterbirds breeding here. Maintaining and improving some of these important characteristics of the lakes will be crucial. Our research shows that the number of pied kingfishers is declining; they nest in holes excavated on vertical mud banks, and these banks have disappeared as the edges of our lakes are covered in concrete or stones to make them into walking paths. With careful planning, we can make our urban lakes friendlier for the birds to live in,” he said.

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