SHIVERING THERMOGENESIS IN THE PIGEON - THE EFFECTS OF ACTIVITY, DIURNAL FACTORS, AND FEEDING STATE

Shivering (electromyographic activity of the pectoral muscle), oxygen consumption, and body temperature were measured from undisturbed pigeo ns for periods of several weeks, and segments from the midparts of eac h phase of the light-dark cycle were compared at various ambient tempe ratures and feeding regimes. Behavior was recorded with a video camera . None of the observed types of behavior (e.g., walking, preening, fee ding, drinking, pecking, defecation) induced spurious electrical activ ity in the pectoral muscle. On the other hand, none of these behaviors directly inhibited ongoing shivering. There was no difference in the mean level of shivering between the light (L) and dark (D) phases of t he day in any of the conditions, although body temperature was 2 degre es C higher during L. Measurements of integrated electromyogram (EMG) with high temporal resolution (28 samples/s) showed that, at 1 degrees C, shivering in the pectoral muscle was present for more than 98% of the time. Plots of oxygen consumption against root mean square EMG wer e obtained in each condition by a filtering procedure that excludes da ta points in which oxygen consumption is affected by motor activity. T hese plots showed that the increase in heat production induced by a un it increase in pectoral EMG was lower in D than in L and that it was f urther lowered by fasting. The amplitude spectra of raw EMG signals we re similar in all conditions. Spectra of demodulated (rectified, low-p ass filtered) EMG showed a distinct rhythmicity around 8 Hz at 21 degr ees C that was further enhanced by fasting but absent at 1 degrees C. This suggests that the degree of synchronization and pattern of recrui tment of motor units are specific for various temperatures and feeding regimes, and may partly explain the variable relation between heat pr oduction and muscle electrical activity. The results emphasize the adv antages of long-term measurements for understanding the control of the rmogenesis in birds.