Wake respirometry allows breath-by-breath assessment of ventilation and CO production in unrestrained animals.

Quantifying stress and energetic responses in animals are major challenges, as existing methods lack temporal resolution and elevate animal stress. We propose "wake respirometry," a new method of quantifying fine-scale changes in CO production in unrestrained animals, using a nondispersive infrared CO sensor positioned downwind of the animal, i.e., in its wake. We parameterize the dispersion of CO in wakes using known CO flow rates and wind speeds. Tests with three bird species in a wind tunnel demonstrated that the system can resolve breath-by-breath changes in CO concentration, with clear exhalation signatures increasing in period and integral with body size. Changes in physiological state were detectable following handling, flight, and exposure to a perceived threat. We discuss the potential of wake respirometry to quantify stress and respiratory patterns in wild animals and provide suggestions for estimating behavior-specific metabolic rates via full integration of CO production across the wake.