Bengaluru's water birds thriving, migratory birds vanishing: Study

Bengaluru’s once-profuse bird populations may have been decimated by urbanisation but scientists have found that resident waterbird populations are on the rise.

Some scientists attributed this to lake rejuvenation activities. Not all is rosy, however, as nearly all migratory water birds which used to visit the city during winter have ceased coming.

According to the study, published in the Journal of Urban Ecology, all but four of 24 migratory waterbird species, including several European-origin species such as northern shovelers, northern pintail and garganey, which traditionally migrated from the United Kingdom during the winter, have virtually disappeared from Bengaluru.

Researchers from the Indian Institute of Science (IISc), Azim Premji University and the Nature Conservation Foundation (NCF) made the findings after surveying some 56 lakes in a radius of 32 kilometres from Halasuru Lake. The study also utilised data uploaded online by citizens to Cornell University’s eBird portal.

The study largely tallied with the scientists’ hypothesis that lakes in the centre of the city will have less diversity as they are most likely to be disturbed and might be polluted. However, they found that lakes further from the city centre showed healthy populations of tree-canopy dwelling birds such as painted storks, pelicans, cormorants, Brahminy kites and egrets.

While this indicates that urbanisation is the primary associate of the decline in lake size closer to the city centre, the findings also show that lake rejuvenation programmes could be working when it comes to restoring ecological balance.

“Bird populations are increasing because of the availability of nesting sites in islands enhanced by lake rejuvenation activities,” said Dr Ravi Jambhekar, a visiting scientist at the Centre for Ecological Sciences at the IISc, who is corresponding author for the study.

He added that the thriving populations suggested that the ecosystem of these rejuvenated lakes could be returning to normal, with an increase of fish.

However, many ground-nesting birds continue to decline. “The pied kingfisher is declining. They nest in holes excavated on vertical mud banks. These banks have disappeared as the edges of our lakes are covered in concrete or stones to make them into walking paths,” noted scientist Kulbhushan Singh Suryawanshi of the Nature Conservation Foundation.

Migratory birds decline

In the case of migratory birds declines, scientists say this could be due to pressures at their home breeding sites in other regions or countries, possibly from feral dogs and cats. For example, nine of the ten migratory duck species previously found in the city were declining. “None of the migratory birds breed in Bengaluru. This is all happening elsewhere,” Dr Jambhekar said.

Speaking as an independent expert, Vishwanth Srikantaiah of Biome said that the “the fact that water bird populations are thriving are an indication that the lake rejuvenation projects are having a positive effect on the environment.”

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