Canaries in the coal emissions: why climate change makes birds change their tune.

The scientists placed the tiny recorders — small enough to fit in the palm of one’s hand — on the ground, hidden at locations ten to 20 feet off the trails, and away from trees, large rocks, and shrubs, which could interfere with recording. The scientists put them in plastic containers to protect them from rain and condensation, but they poked holes in them so the recorders could “breathe.”