Welcome to the little known Jubilee Lake Mega (giant) Bat sanctuary - the state's lone urban bat reserve - on a 0.69 hectare island inside the Tata Steel Zoological Park in the heart of this industrial town in eastern India. The bat population here has logged a sharp rise from 500 in 2008 to 700 in 2009, according to a census carried out by zoo authorities and local researchers this week.

The sanctuary boasts of two of the largest bats in the world -- the herbivorous flying fox (Pteropus giganteus) and the sphinx (Cynopterus sphinx) -- natives of the tropics and the sub-tropics.

"In 2006-07, K.K. Sharma, who heads the department of zoology of the Jamshedpur Cooperative College, carried out a survey with a group of students and found that the number of giant fruit bats had shrunk in the steel city and in the neighbouring Dalma Wildlife Sanctuary, barely 10 km from the city. They were once found in abundance in and around the city and across the East Singhbhum district,"  zoological park director Bipul Chakrabarty said.

"Sharma found that a colony of 500 bats had localised themselves on the island inside the (14-hectare) Jubilee lake, which fell under the purview of the Tata Steel Zoological Park. He approached the park to protect them, create safe roosting sites and a stable food chain. The Tata Steel Zoological Society declared the island a bat sanctuary in 2008."

The island has several fruit-bearing trees of the ficus family like figs -- a staple diet of the giant fruit bats. The dense greenery of the park, home to fruit-laden trees like papayas and mangoes, also ensure ample food for the bats.

"The fact that the habitat is an island helps. Bats are naturally attracted to water. After returning to their nests early in the morning, clusters of them swoop down into the lake for sips of water," said Chakrabarty, who has worked for 15 years at the Central Zoo Authority.

The zoo authority and local environmentalists led by Sharma protect the bats by "giving them seclusion, removing them from human contact and filling the island with more greenery". Local tribals of Jharkhand hunt flying foxes for their meat which is believed to cure respiratory diseases, Sharma said.

According to him, the reasons for the earlier decline in the bat population in Jharkhand are "human interference and the flying mammals' fussy nature.

"Bats are very choosy about habitats. They prefer trees of the ficus varieties -- like large fig and banyan trees -- to roost and easy access to water."

The giant flying foxes or the "megachiropterans (mega bats)" and sphinx (medium-size bats) found in the sanctuary weigh between 1 and 1.5 kg with an average wing-span of 1 to 2 metres, Sharma said.

The zoo authorities and local researchers are drawing up the final blueprint for a mega bat conservation project. "We will submit the project to the ministry of environment this month," Chakrabarty said.

The project -- a collaboration between the Tata Steel Zoological Park and Sharma -- will study the "behavioural aspects of large bats, factors for their decline in the state, breeding habits, scope for captive breeding, seasonal migration and colonies elsewhere in the region", Sharma said.

"We would like to create sacred groves for the bats across the state because the topography and biodiversity of Jharkhand encourage growth of bats. The flying mammals are very important for the preservation of natural food chain because they help germinate at least 50 varieties of fruits. Bats drop digested fruit seeds as fecal matter on the ground while flying and these seeds germinate only after passing through the guts of the big fruit bats. Bats also carry pollens across the forests. We want to regenerate the forests of the state by creating more mega bat habitats."

According to the Britain-based Bat Conservation Trust, there are more than 1,100 species of bats across the world accounting for one-fifth of all mammal species.