U.S. Fish and Wildlife Service, Marvin Moriarty, Associated Press
This March 26, 2009 photo provided by the U.S. Fish and Wildlife Service shows a little brown bat with white-nose syndrome in the Greeley Mine in Stockbridge, Vt. Scientists studying the mysterious ailment that has killed millions of bats in North America said in December 2011 that they are again finding small groups of surviving, healthy bats.

MONTPELIER, Vt. — Scientists studying the mysterious ailment that has killed millions of bats in an epidemic that is spreading across North America say they are finding small groups of surviving, healthy bats.

The scientists don't know why, and it's too soon to say if the surviving colonies found in Vermont, Pennsylvania and elsewhere could eventually repopulate the region. But they are planning to study the survivors in hopes of finding answers.

The scientists are planning to meet next month in Pennsylvania to seek the best ways to learn from the survivors.

Scott Darling of the Vermont Department of Fish and Wildlife says biologists have found 15 colonies in the western part of the state where bats are surviving and appear to be healthy.