BENGALURU: A study done in Bengaluru has found that migratory bird numbers are declining in the city, while the numbers of many resident birds dependent on lakes seem to be increasing in the past five years. These declines in migrant species are likely to be associated with conditions in the breeding grounds rather than in the wintering grounds in the city, said the study titled "Relationship between lake area and distance from the city centre on lake dependent resident and migratory birds in urban Bangalore, a tropical mega-city in Southern India". It has been published in the Journal of Urban Ecology.
Authored by Ravi Jambhekar, Kulbhushansingh Suryawanshi and Harini Nagendra, the paper investigates how the number of bird species found in Bengaluru's lakes is related to the degree of urbanisation in surrounding areas. This study is unique because it uses data collected by residents of Bengaluru and uploaded to the eBird portal.
"Birds that nest in tree canopies such as cormorants, painted stork, Brahminy kites and egrets are increasing. This might be because of the availability of nesting sites in the islands with tall trees, created by the authorities. Many of these species are also piscivores (fish-eaters) and another reason for their increase could be the increase of fish in the lakes, the main prey of these birds," read the study done by Azim Premji University and the Nature Conservation Foundation.
Ravi Jambhekar, Visiting Scientist, Centre for Ecological Sciences, Indian Institute of Science, said, "We speculate that the decline behind migratory bird populations might be because of some changes happening in the breeding grounds but lake restoration and creation of islands in the lakes is helping resident birds."
Kulbhushan Singh Suryawanshi, Scientist, NCF, spoke about the declining numbers of species like the pied kingfisher and how it can be avoided.
"Maintaining and improving some of these important characteristics of the lakes will be crucial. Our research shows that the pied kingfisher 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.
This study found that the size of the lake area and its distance from the city centre are correlated to the number of bird species that occur at the lake; larger lakes support more bird species. As the distance from the city centre increased (i.e. urbanisation decreases), the number of bird species increased. Larger lakes support more diversity compared to smaller lakes as they are likely to have more resting and breeding spaces, feeding resources and microhabitats required for birds. Lakes in the centre of the city have less bird diversity 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.
Fish-eating birds such as cormorants and oriental darters 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.
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).