MUSCLE TREMORS AND THE DEVELOPMENT OF TEMPERATURE REGULATION IN BIRDS

Abstract

The development of coordinated muscle tremors, such as are picked up and recorded by the cardio-vibrometer, corresponds closely with the development of temp. regulation in the small altricial sp.[long dash]the house wren and black-capped chickadee. No tremors were recorded from newly hatched and 3-day nestlings which are poikilothermic but were present at all later ages roughly corresponding to the development of homoiothermy and inversely related to the air temp. At 95oF. (35[degree]C.) (and also at first appearance in ontogeny) tremors were often periodic in occurrence; with a decrease in temp. tremor periods tended to increase in duration and frequency until shivering became continuous. During active periods the frequency of tremors (as indicated by total body vibrations) was 30 to 40 per sec. The muscle tremor heat production mechanism apparently develops more rapidly at first than does the control of heat loss as indicated by feather growth. In the precocial pheasant periodic tremors were first detected at 9 days of incubation in the unopened egg at incubation temp.