ИСТИНА

Electrocardiogram (ECG) in freely moving altricial pied flycatcher (Ficedula hypoleuca) nestlings was studied from the 1st posthatching day till fledging at day14-16 and in fledglings till the 21st day. Nestlings were housed in a heated chamber imitating a natural nest; ECG was recorded via subcutaneous silver electrodes. Body temperature (TB) was measured with thermocouple placed under wing. Heart rate (HR), QRS amplitude and TB were analyzed during feeding, thermoregulation and defense behavior. Mean HR increased linearly from 450 beat/min after hatching to 650 beat/min at day 14 (before fledging). The ranges of HR changes were 300-650 beat/min at the 1 st day and 400-1000/min at the 21 st day. During prolonged cooling, HR changed linearly with TB. HR increased by 37±3 beat/min with ТВ increase by 1 ºС in the range of TB up to 37 ºС. Within the range of ТВ= 37-42 ºС the relation was inversed – heart rate declined with ТВ increase. Before the effective thermoregulation established at day 8-9 the lowest values of HR were determined by ТВ under cooling. For the nestlings prior to established thermocontrol the critical TBcr was determined as TB level to which a nestling could safely be cooled while still manifesting feeding and defense responses and being able to recover quickly when heated. ТBcr=24,4+1,3D (ºС), where D is nestling’s posthatching age in days. Thermoregulation shivering and defense freezing were accompanied by ТВ increase due to the activity of pectoral muscles. The highest values of HR appeared during begging in nestlings and during defense reaction in fledglings. Since the moment of hatching, the parental acoustic food call and mechanical stimulation of gullet induced a 10-30% HR increase, a 30-200% QRS amplitude increase and begging. After eyes opening at day 5-6, the same effect was caused by luminosity change imitating the one resulting from a parent passing through the entrance-hole in the wild. At day 8-9, moving parent’s silhouette began to induce HR increase and begging. In the nestlings aged 5-13 days, parents’ alarm call caused defense behavior –freezing, which was accompained by bradicardia when the initial HR was relatively high and ТВ was 37-38 ºС. On the eve of fledging defense reaction may be manifested in increasing of HR.