DEVELOPMENT OF HEART-RATE IN THE PRECOCIAL KING QUAIL COTURNIX CHINENSIS

Our aim was to examine changes in heart rate (fH) during the embryonic and posthatching periods of the smallest precocial avian species, Cot urnix chinensis. In experiment I, repeated measurements of mean fH wer e made for individual quail by ballistocardiogram (BCG) during incubat ion, and by both piezo-electric film and electrocardiogram (ECG) durin g the posthatching period (resting and thermoneutral conditions). Mean fH of all embryos increased during the second half of incubation and the first week posthatching, but a few embryos experienced a very brie f period of decreased fH prior to internal pipping, After the first we ek, fH of posthatching quail was maintained at high levels (550-650 be ats min(-1)), then decreased with age and increase in body mass. The m aximal fH Of quail chicks represents a greater posthatching increase i n f(H) than is found in larger precocial chickens, this difference bei ng attributable to the higher demands of thermoregulation at small bod y masses in the quail. In experiment II, the mean fH of quail embryos (day 2-16) was recorded by EGG, and embryonic stage, yolk-free embryo mass (wet and dry) and water content were measured. Mean fH was linear ly related to embryo mass throughout incubation, except on the day pri or to internal pipping, when the fH of a few embryos declined below th is linear relationship. Measurements of instantaneous fH of late incub ation embryos, young and adult quail all showed spontaneous fluctuatio ns in fH, Two main frequency components of fH fluctuations were identi fied for the first time in an avian species. Low-frequency (mean 0.09 Hz, 12.6 s) and high-frequency (1.4 Hz, 0.9 s) oscillations in both yo ung chicks and adult quail were detected and are considered to reflect baroreflex mediation of fH and respiratory sinus arrhythmia, respecti vely.