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.
A quiet recording is not an empty sea
Acoustic non-detections are traced through the links between animal presence, sound production, propagation, recorder performance, and classification. The essay uses a hypothetical comparison of continuous and intermittent recording to show why deployed days or simple hourly adjustments can misrepresent listening effort when calls occur in bouts. Changing background noise, sensitivity, and detector thresholds can also change detections without a matching change in abundance. Drawing on NOAA's acoustics guidance and data portal, it argues for representative manual review, uncertain classifications, and explicit separation of lost, rejected, unrecorded, and analysed intervals. Visual observations can add evidence but retain their own limits. The defensible conclusion concerns calls detected under a stated method; claims about absence or density require stronger detection assumptions and knowledge of call rates.