Artificial light at night disrupts bat echolocation, foraging behavior, and colony emergence timing, with welfare implications for insectivorous bat populations in increasingly light-polluted environments.
Bat welfare impacts from light pollution are chronic, cumulative, and invisible to most people. A light-averse bat colony whose roost exit is illuminated experiences nightly foraging time reduction that affects energy intake across the entire active season. Over a summer, reduced foraging time translates into lower fat reserves entering hibernation, lower pup survival from underfed mothers, and higher winter mortality. The welfare cost to individual bats is real and significant despite being entirely invisible to the humans whose lighting decisions create it. Simple mitigation through directional lighting, motion sensors, and wavelength-appropriate bulbs can substantially reduce these impacts.