By Subir Bhaumik
BBC News, Calcutta
Elephants in the Indian state of West Bengal are to undergo a birth control scheme due to a lack of funds for their upkeep, the state government says.
India's elephant population is in decline
Of West Bengal's 400 elephants, nearly 70 are tame and in service to private owners or the state forest department.
Forest guards use them to patrol the many wildlife sanctuaries.
But wildlife conservation groups have been angered by the proposed introduction of such birth control methods for the elephants.
The Bengal Forest department spends more than 60m rupees (about $1.3m) annually on the upkeep of the elephants in its service.
"But our department is suffering a budget cut, so we have been asked to only maintain those elephants that are useful and introduce birth control amongst the whole population," said forest official PT Bhutiya.
There are three-to-four births annually among the elephants in the service of the forest department, Mr Bhutiya said.
He added that only 30 of these elephants are used to guard the state's wildlife sanctuaries.
Veterinary doctors would administer birth control injections and pills on about a dozen female elephants in the service of the forest department, he said.
"This is just a killing exercise," Mukuta Mukherjee, coordinator of environmental group Friends of Wetlands and Wildlife, said.
"If the government cannot feed the elephants, they should look for sponsors but not do anything to cut down their population."
She said the forest department should release captive young elephants males into the wild or find alternative sources of funding, instead of preventing them from reproducing.
Ten years ago, India was home to more than 50,000 wild elephants, but poaching and habitat shrinkage has led to a decline in their population.
Ivory tusks in thousands are recovered from smugglers in India every year, indicating mounting kills.