61.7 Friday, Jan. 6 Heart rate is not modulated with flight speed in cockatiels ROS, I.G.*; BIEWENER, A.A.; Harvard University; Harvard University email@example.com
We examined how heart (HR) varies as a function of flight speed in a flying bird, examining changes in HR of cockatiels (Nymphicus hollandicus) flying in a wind tunnel at different speeds. In mammals, heart rate (HR) correlates well with the rate of metabolism (metabolic power), indicating that heart rate is adjusted to meet the oxygen demand for a particular level of exertion and that increased oxygen demand at higher metabolic power is (at least partially) met by increased cardiac output. Measurements of the rate of respiratory oxygen consumption (VO2) can be used to estimate metabolic aerobic power for animals that burn fuel using oxidative phosphorylation. However, respirometry is experimentally challenging to achieve for flying birds over a range of sustained flight speeds, and relatively few studies have successfully accomplished this. Assuming a strong correlation between HR and VO2, HR measurements have been used to estimate the metabolic power requirements of freely flying birds. We therefore hypothesized that HR would correlate with metabolic power in cockatiels across a range of flight speeds. Aerodynamic theory predicts and empirical data confirm that for cockatiels metabolic power varies with flight speed as a U-shaped power curve. HR was measured by implanting EKG electrodes over the dorsum of the bird’s thorax. Surprisingly, we found no change in HR during steady flights across a wide range of flight speeds (0-16 m/s), indicating that cockatiels do not adjust HR to alter oxygen supply to their flight muscles. Instead, HR remained constant across the entire range of flight speeds at 817 ± 5 beats/min (mean ± SD across all flight speeds), elevated about 2.3-fold relative to the resting value (356 ± 2 beats/min). We therefore suggest caution when using heart rate as a proxy for estimates of metabolic power during avian flight.