THE DEVELOPMENT OF THERMOREGULATION IN THE NESTLINGS OF THE TREE SPARROW

This paper deals with the development of the thermoregulation of nestlings of the tree sparrow (Passer montanus saturatus). Seventy-four nests totalled 256 nestlings of various ages were used to determinate their oxygen consumptions and to measure their body temperatures at 5℃-35℃ ambient temperatures.In a few days after hatching, the body temperature of nestlings varies with ambient temperatures between 10℃-35℃ in a typically poikilothermic manner (Fig. 1). When ambient temperature was above 30℃, an increased difference between the body temperature of 6-day-old nestlings and the ambient temperature was observed, while at 7 to 9 days of age, at ambient temperatures between 5℃ and 35O℃ the difference was evidently bigger. Tree sparrows of 10 to 13 days old were have ability to maintain constant body temperature, as a homeothermie manner (Fig. 2). When body temperature is below 12.0℃, nestlings younger than 8 days of age were in a paralytic state. In an extreme case, the body temperature of some individuals could be dropped as low as 5℃ for a short period, they could still recover.At 10℃, the oxygen consumption increased rapidly in 7-9 days old, while after 10 day old, it remained almost constant. The oxygen consumption of nestlings decreased daily with age in first few days after hatching at 20℃ and 30℃, and then increased gradually after 3-4 days old. A rapid increase in oxygen consumption during 4-9 (20℃) or 4-7 (30℃) days old was observed.The instantaneous increasing rate of oxygen consumption of nestlings at 10℃, 20℃ and 30℃ was calculated according the formula M = Aekt. From the data obtained, it was postulated that the increasing rates of oxygen consumption were different with different ages of nestlings. There were practically 4 stages i.e., 0-4, 4-7, 7-10 and 10-13 days of age with 4 different rates of oxygen consumption (Fig. 3). The oxygen consumption of 0-5 day old birds was approximately proportional to ambient temperature (Fig. 4), The first indication of an inverse proportion between oxygen consumption and ambient temperature was observed in 6 days old at temperature between 30℃ and 35℃, and then appeared again at 7-10 days old birds at ambient temperature between 10℃ and 35℃. A homeothermic pattern of metabolic response to ambient temperature had appeared after 10 day old. In this period the mechanizm of thermoragulation was established.At 10℃, 20℃ and 30℃, the correlations between oxygen consumption and body weight of nestlings throughout the whole nestling period appear to be distributed in four segments (Fig. 5). According to the formula M = aWb the value of exponent b for these segments is calculated, and it varies with body weight. First segment (about 0-3 days) is negative correlation (20℃ and 30℃ ). The seconds segment (4-6 days) is positive correlation. The 3nd segment (7-9 days) also is positive correlation. (10℃-20℃ ), while at 30℃ it is negative correlation. The 4rd segment (10-13 days) is negative correlation.At ambient temperature below 25O℃ , chill tremor first was preceated in 7 days of age, and nestlings of 9 days of age had appeared fluffing as reduced heat dissipation . In 8 days of age panting appeared first which served as the way to the dissipate heat accumulated by the body at ambient temperature above 35℃ . Based on pattern of development of thermoregulation, it is possible to distinguish three stages in the nestling period of the tree sparrow. The first stage, from 0 to 3 days of age, is poikilothermic period. The second stage, 4-9 days of age, is a period of development of thermoregulatory ability. This stage may be classified into two periods: period of 4-6 days of age is slowly development of thermoregulatory ability; the period of 7-9 days of age is the period that thermoregulatory ability develops very rapidly. The 3rd stage, 10-13 days of age, a period when a complete thermoregulatory mechanism was established, was the homoeothermic period.