Fig. 2

ECG traces in blue petrels. A ECG traces of three blue petrels measured in milliVolts (mV) showing P, R and T waves corresponding to atrial depolarization, ventricular depolarization (heartbeat) and ventricular repolarization, respectively (see methods). Not all recordings had the quality necessary to identify P and T waves, but R waves were always identifiable. B Comparison of blue petrels’ HR under incubation (basal) and during disturbance before egg substitution (n = 4). *p = 0.0425, t = 3.397, df = 3, by paired two-tailed T-test; n = 4