Cardiac responses in alarmed red deer calves.

Radio transmitters were used to record the ECG signals of young red deer calves (Cervus elaphus) when they were exposed to various stimuli which elicited the immobility or "freezing" response. When the calves were exposed to stimuli likely to occur in the deer's natural habitat, the heart rate decreased by 25 to 85% of the pre-exposure rate. The calves displayed a more pronounced bradycardia during their first days of life than at a later age. There are also indications that repeated exposure to the same stimulus will cause a gradual waning both of the bradycardia and of the behavioural response.