NASSAR, P. N.*; CARRIER, D. R.; Univ. of Pennsylvania, Philadelphia; Univ. of Utah, Salt Lake City: Ventilatory patterns of guinea fowl Numida meleagris during terrestrial locomotion and evidence for gearing in the avian respiratory system

While locomotor-respiratory entrainment has been observed in a number of exercising mammals and flying birds, no study has given a detailed account of this phenomenon in running birds. Guinea fowl were run at gradually increasing speeds (1.35-3.17 m/s) on a motorized treadmill (N=5 birds). Ventilatory data were collected by having the birds wear a screen-mesh pneumotachograph mask, while footfall data were collected by placing a vertical accelerometer on the bird’s back. Breathing frequency (f), tidal volume (V_T), and minute volume (VE) were observed throughout the duration of the trial. Guinea fowl displayed 3 to 4 discrete coupling ratios: 2:1, 1.5:1, 1:1 and 0.5:1 (strides:breaths), the latter two ratios being associated with thermoregulatory panting. Breathing frequency, V_T, and VE were positively correlated with speed, though at the highest speed and highest coupling ratio, 0.5:1, all three variables leveled off, consisten with mechanical models of ventilation. The increase in minute volumes that occurred when the birds shifted from lower to higher coupling ratios (e.g. 1.5:1 to 1:1, 1:1 to 0.5:1, etc.) suggests that the avian respiratory system may be “geared” to economize the work of breathing. Because entrainment is often found in animals that also possess high levels of aerobic activity, the establishment of entrainment in modern birds during terrestrial locomotion is a key step in trying to deduce the activity levels of extinct avian and non-avian archosaurs.