Entry-Light Protocols for Winter Hibernaculum Visits

Some winter visits are unavoidable. When a biologist has to enter a hibernaculum, the light they bring matters — not just the brightness, but the color, the direction, and the dark-adaptation time on either side of exposure. EchoQuilt provides the map that makes lights-off navigation practical.

A January 2022 emergency access into a Virginia Myotis sodalis hibernaculum — triggered by a partial entrance collapse that threatened winter airflow — forced a three-person team to spend 90 minutes underground during deep torpor. The team had one objective (inspect the entrance, confirm airflow, exit) and one constraint (minimize photic and thermal disturbance to the 2,200-bat cluster 35 m back in the chamber). Using a standard white headlamp would have spilled light into the cluster volume even at the entrance work area, based on prior lux measurements. The team ran the inspection with red-filtered headlamps kept below 3 lumens, worked with backs turned toward the cluster, and carried a printed EchoQuilt floor plan to navigate without sweeping lights across the passage. The post-visit acoustic record showed zero detectable arousals.