Chemistry & migration mysteries: Fur holds clues to previous journeys

The bat was not only pregnant but downright angry as I snipped a bit of fur from her back. Within a few seconds, however, she flapped her powerful wings, took off from my hand and disappeared into the night, rejoining thousands of female hoary bats (Lasiurus cinereus) on their migration through the mountains of New Mexico.

Every spring, hundreds of these expectant mothers pass through this small stream drainage on their way to birthing grounds farther east. Their annual passage was first reported here more than 30 years ago, and it is still one of the few known migration corridors in the area.

My task that night was simple: catch hoary bats and snip tiny samples of fur from their thick coats, then let them continue on their way. The explanation, however, is a bit more complicated.