Bats are Pennsylvania's only true hibernator, and they place strict requirements on the sites they choose. Stable temperatures, proper humidity, easy access, good surrounding foraging habitat, and no disturbance are key factors.
Compound all this with the fact that each species insists on a slightly different temperature. This means the underground passages must be laid out in a certain way to make a stable temperature gradient. 100 years ago, mine owners did not have today's bats in mind!
An abandoned limestone mine in Canoe Creek State Park was bulldozed shut one winter, a typical way to deal with such places across Pennsylvania. Unfortunately at the time it was winter home to thousands of bats, including a handful of federally endangered Indiana bats.
Officials realized the potential to conserve a significant rare site and manage it for wildlife. Debris was re-excavated from the top of two entrances and a protective gate installed.
Today the mine contains nearly 15,000 residents from all six species which over winter in Pennsylvania. Among these are over 300 Indiana bats.