The Bracken Bat Cave outside San Antonio, Texas will have another lease on life because of a new deal.

The night sky around the bat cave will stay dark and the mother and baby bats inside will have a buffer between them and the hazards of city sprawl because of a US$20 million deal signed on Friday by Nature Conservancy and local and state government officials of San Antonio and local developers.

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The bat cave is one of the biggest bat colonies in the world and is home to 15 to 20 million bats. It houses a large number of pregnant female bats and becomes a massive maternity ward for them.

The bats spend winter in Mexico before returning to San, Antonio. Every 7:30 in the evening, millions of bats spiral out of the deep cave and streak off toward the darkening southern sky.

The bat cave was threatened in 2013 when a developer said it would build 3,500 residential homes beside the cave.

"We would have had hundreds of bats congregating on the porches, around street lights, around swimming pools. Baby bats that were either resting or sick, or older bats that were sick, might be found by family pets and brought into houses," said Bat Conservation International (BCI) Executive Director Andy Walker.

Walker said bats are attracted to houses and light. Conservationists are worried about the impact of humans on bats while state officials are concerned about the spread of bat rabies among humans.

San Antonio Councilman Ron Nirenberg teamed up with two counties, conservation groups, donors and others to raise money and buy the land from the developer to widen the buffer zone around the bat cave.

TagsBat Colony, Bracken Bat Cave, bat cave, Bat Conservation International, bat conservationists