Missing observations are not zeroes

A missing observation, a usable recording with no detections, and a signal obscured by noise support different conclusions. This essay uses hypothetical acoustic records to distinguish counts from effort-adjusted rates and to show why downtime must not become successful listening. It draws on Climate and Forecast conventions to discuss missing-value codes and separate quality flags, including the care needed for values below reporting limits. NOAA's observing-network assessment supplies context for uneven seasonal and spatial coverage. When gaps depend on weather or access, the remaining record may not represent the full conditions of interest. The practical recommendation is to preserve reasons for absence, coverage rules, method changes, and visible chart gaps, while distinguishing estimated values from measurements and never treating zero detections as proof of animal absence.