Biologist Ashley Wilson carefully disentangled a bat from netting above a tree-lined river and examined the wriggling, furry mammal in her headlamp’s glow. “Another big brown,” she said with a sigh.

It was a common type, one of many Wilson and colleagues had snagged on summer nights in the southern Michigan countryside. They were looking for increasingly scarce Indiana and northern long-eared bats, which historically migrated there for birthing season, sheltering behind peeling bark of dead trees.

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