The Rococo-style library of the National Palace of Mafra in Portugal holds 36,000 leather-bound volumes dating from the 14th to 19th centuries. Also part of the collection? Bats. Atlas Obscura Podcast talks to librarian Teresa Amaral and bat biologist Hugo Rebelo about these tiny nocturnal creatures, why they’re welcome in the library, and the “cost-free” service that this “night shift” provides.