Stillness and habituation do not prove absence of impact. Preserve what was measured and what remains unknown.
2015: Pair movement with physiology
Ditmer and colleagues paired movement and heart-rate measurements in wild American black bears. Overt behavioural changes were uncommon, but heart rates rose, with a reported maximum increase of 123 beats per minute above baseline. That maximum is not a population average. The study demonstrates an acute physiological response that visible movement alone could miss.
2019: Habituation is a narrower finding
A subsequent study of five captive bears found diminishing cardiac responses with repeated flights and persistence after a 118-day pause. The authors cautioned about transfer to wild animals and unmeasured chronic effects. This finding does not establish that repeated exposure is harmless or that wildlife should be deliberately habituated to survey aircraft.
Design implication: Join two observation streams
Airffic proposes storing flight events and animal observations separately while preserving a shared time reference. Adding physiological measurements can itself require handling or instrumentation, so its burden belongs in ethical review. More sensors do not automatically improve welfare. The study team must compare the information required for the question with the burden of collecting it.
Operational implication: Keep unknowns visible
Before recording “no response,” check how long the animal was observable and which response was measured. Occlusion is an observation gap. The proposed report separates observation coverage, recorded changes, stops or deviations, and review actions. This prevents an attractive image from being mistaken for evidence that the welfare protocol was satisfied.
Evidence & further reading
Check the original study conditions, species and location before using a result in a plan. Do not transfer findings universally across species and settings.