Jan. 15: If Bengal were poll-bound Uttar Pradesh, Mayawati might have trumpeted this as a triumph.

Migrating elephant herds appear to like Mamata Banerjee's Bengal so much - unlike hardened investors - that they spend more time here than in the neighbouring states from where they cross over.

In the 2014 census, the south Bengal districts of West Midnapore, Bankura and Purulia were found to have an elephant population of 150, of whom around 100 had crossed over from adjoining Jharkhand. "These herds are now spending close to 10 months in Bengal and only two in Jharkhand," Subhankar Sengupta, conservator of forests (wildlife), told Metro.

This and other such curious facts would be authenticated by a synchronised field estimate of the country's elephant population, to be carried out in phases by clubbing together states that share boundaries and wildlife corridors.

The synchronised survey is scheduled to start in the south Bengal districts in April along with Jharkhand, Odisha, Chhattisgarh, Bihar and Andhra Pradesh. The north Bengal districts of Jalpaiguri, Alipurduar and the foothills of Darjeeling have been grouped with Assam, said Pradeep Vyas, the principal chief conservator of forests (wildlife).

The last census in north Bengal, which has several national parks and the Dooars forests, had pegged the elephant population there at 650.

Population estimations carried out every five years have so far not followed a uniform methodology, leaving room for error. This time, all states have been asked to not only map the population distribution but also create a database split into various sections - males, females, adults, calves and tuskers.

The objective of a synchronised programme is to help reduce the possibility of "overestimation or underestimation" when states with contiguous boundaries do field-level counting on different days. "Since elephants cross over in search of food or favourable climate, it is practical to do a simultaneous head count in contiguous habitats," said an official of the wildlife division.

The forest departments of the participating states are required to pass on the field data to the central government. The final figures will be published about three months after all states submit their data.

India's elephant population during the last such exercise in 2012 was estimated to be 30,000.

Raman Sukumar, a professor at the Indian Institute of Science, Bangalore, and founder of the Asian Nature Conservation Foundation, is co-ordinating plans for the synchronised survey on the central government's behalf. "Besides the standard headcount, all states will have to report figures based on the dung decay method. Field work will be done in the dry season when most elephants stay inside the forests," Sukumar told Metro over the phone.

The dung decay method is an indirect way of estimating the elephant population in a location by tracking excreta.