The Mystery of Sambhar Lake: Why are so many birds dying in Rajasthan?

Hamza Khan
Sambhar Lake: A civic worker carries a dead bird at the Sambhar Salt Lake in Rajasthan, Monday, Nov. 11, 2019. (PTI Photo/File)

On November 10, visitors at Sambhar Lake, India's largest inland saltwater lake located about 80 km southwest of Jaipur, spotted a very large number of dead birds.

Over the following week, their unpleasant discovery manifested itself as a crisis of disturbing dimensions -- until Tuesday (November 19), the Rajasthan government had, using various agencies, buried a total 17,454 dead birds to prevent the spread of infection. A total 8,559 birds were disposed of in Jaipur, and 8,895 in Nagaur.

Why and how did these birds die?

Nearly 10 days into the tragedy, the government is yet to determine the cause of the deaths. The investigation so far points to avian botulism -- a paralytic, frequently fatal disease caused by the ingestion of toxins -- as a possible cause. This has not, however, been officially confirmed.

After studying bird samples, the Apex Centre for Animal Disease Investigation, Monitoring and Surveillance at the College of Veterinary and Animal Science under the Rajasthan University of Veterinary and Animal Sciences (RAJUVAS), Bikaner, has said in its report: "On the basis of history, epidemiological observations, classical clinical symptoms and post-mortem findings, the most probable diagnosis is avian botulism.

"The clinical signs exhibited by affected birds included dullness, depression, anorexia, flaccid paralysis in legs and wings, and neck touching the ground. The birds were unable to walk, swim, or take flight. There was no rise of body temperature, no nasal discharge, no respiratory distress or any other sign."

But why is it taking so long to ascertain the cause of the deaths?

The government is waiting for reports from various institutes to determine the exact cause with certainty. It has so far engaged eight agencies or institutes to study the phenomenon, but has received complete reports from only two: RAJUVAS and the National Institute of High Security Animal Diseases (NIHSAD) in Bhopal.

While RAJUVAS has pointed to avian botulism, NIHSAD, after carrying out tests on samples, has ruled out bird flu.

Partial reports have been received from the Wildlife Institute of India, Dehradun, as well as the Rajasthan State Pollution Control Board.

Reports are awaited from the Indian Veterinary Research Institute, Bareilly, The Salim Ali Centre for Ornithology and Natural History (SACON) in Coimbatore, the Bombay Natural History Society (BNHS), and Sambhar Salt Limited.

OK, so broadly, what could be the possible reasons?

After a Division Bench of the Rajasthan High Court led by Chief Justice Indrajit Mahanty took cognizance of the bird deaths, the Rajasthan government listed four likely reasons.

* Viral infection

* Toxicity, as new area has been filled up after almost 20 years, and there could be higher concentration of salts along the edges

* Bacteriological infection

* Higher temperature and high water levels due to good monsoon might have led to an increase in intra-species and inter-species competition for resources. The weaker individuals, exhausted from the long journey, perhaps were unable to compete, and may have succumbed to stress emanating from the shortage of food, susceptibility to disease/pollutants/toxins and other habitat-related factors in the wintering grounds. In such an eventuality, it is expected that with fall of temperature and lowering of water levels, the incidence of such mortality will go down.