Thousands of migratory birds of about ten species were found dead around Sambhar Lake, the country's largest inland saltwater lake near Jaipur, sending shock waves among locals and authorities.

This is the second such incident in the state within a week. Last Thursday, 37 demoiselle cranes were found dead in Jodhpur's Khinchan area.

Authorities have initiated rescue efforts and have sent their viscera to pathology labs in Ludhiana and Bhopal for further investigations for the suspected cause.

At Khinchan, officers are suspecting pesticide-laden seed in a particular field as the cause of death.

Officials also said that they suspect water contamination as one of the reasons for the deaths but were awaiting viscera test reports. Though the official toll was 1,500, locals claimed the number of dead birds could be as high as 5,000.

"We have never seen anything like that. Over 5,000 birds died mysteriously all over the place," 25-year-old Abhinav Vaishnav, a local bird-watcher said.

When Vaishanav went on a stroll along the edge of the lake on Sunday, he took the hundreds of dark lumps strewn across the marshy land for cow dung. But it didn't take him and his fellow bird watchers Kishan Meena and Pavan Modi to realise the lumps were bodies of hundreds of lifeless migratory birds.

Carcasses of hundreds of dead birds including plovers, common coot, black-winged stilt, northern shovelers, ruddy shelduck, and pied avocet were scattered on the edge of 12-13 km of the catchment area of the lake, leading to a possible number of over 5,000, they said.

Forest ranger Rajendra Jakhar said a possible reason could be the hailstorm that hit the area a few days back.

"We estimate about 1,500 birds of about 10 species have died. We are also looking at other possibilities like toxicity of the water, bacterial or viral infection," he said.

A medical team from Jaipur has collected a few carcasses and water samples are being sent to Bhopal for further examination.

Ashok Rao, a veterinary doctor and part of the team, said that while the exact reason for the deaths was uncertain, he ruled out the possibility of bird flu.

"At the initial examination, we did not find any sort of secretion from the birds, which is a giveaway in the cases of bird flu," he said.

RG Ujjwal, nodal officer, animal husbandry department, joined Rao and listed possible reasons behind the mysterious calamity.

"There could be some sort of contamination in the water. The increased salinity of the water could also be another reason, as it increases salt concentration in the blood, which can further lead to slow blood flow and the internal organs like the brain may stop working," Ujjwal said.

The lake is also a favourite of flamingos, stilts, stints, garganey, gulls and a number of other species of birds.

Jakhar informed that the lake every year hosts approximately 2-3 lakh birds, which include about 50,000 flamingos and 1,00,000 waders.

The strange episode has left villagers and people of the forest department baffled for the lack of a sensible explanation.

An officer said higher temperature and deep water because of the good rainy season can also lead to such mortality as birds are unable to eat properly after being exhausted by a long flight.

"I have never seen such a thing in 40 years of my service in the forest department. First I thought it could be because of the hail, but that occurs every year. There is no chemical waste in this water either," said Ramesh Chandra Daroga, a local working with the forest department.

Ashok Sharma, joint director, State Disease Diagnostic Centre, said that once the reason was ascertained further steps will be taken.

"We don't think it is a case of infection, but if it turns out to be the case we will take further steps to make sure it doesn't spread," he assured.

Meanwhile, the carcasses were collected in a tractor-trolley and buried in a ditch. A total of 669 dead birds were buried while hundreds lay strewn around as the forest staff hesitated to venture into the slippery muddy areas.

-(With inputs from PTI)