Diurnal Activity Cycles in Captive and Free-Ranging Indian Ocean Bottlenose Dolphins (Tursiops Ad Uncus Ehrenburg)

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[The behaviour of four captive Indian Ocean bottlenose dolphins (Tursiops aduncus)-a bull, two cows (adult) and a female calf-was observed for a total of Io4.5 hours during regular 30 minute observation sessions, conducted on a random basis at all times of the day, between March and November, I970. Units of precopulatory and copulatory behaviour were defined and quantified together with concomitant whistle-phonation in relation to the time of day. The frequency of social interactions was significantly influenced by a diurnal cycle. Social behaviour was infrequent at night and in the early morning, but increased significantly to reach a peak at midday and in the early afternoon Whistle-phonation rarely occurred at night and was still infrequent in the early morning. The behavioural roles in courtship contexts were interchangable between age and sex classes and sexual partners adopted identical courtship display postures with equal frequency. Free-ranging bottlenose dolphins were studied in three areas along the eastern Cape coast: Algoa Bay (34°S.25°E.), the Tsitsikamma Coastal National Park (34°S.23°E.), and Plettenberg Bay (34°S. 23°E.) Bottlenose dolphins were sighted on 122 occasions and were observed for a total of 79.7 hours between Janary I970 and May I97I. A systematic watch during all daylight hours was maintained for dolphins during three seasonal field trips to Plettenberg Bay. The dolphins entered the Bay mainly in the early morning and in the late afternoon. Feeding procedures and co-ordinated herding of food-fish by schools of bottlenose dolphins was described. The units of social behaviour scored in captivity, including mating attempts by bulls, were also observable under free-ranging conditions. Feeding was most frequent in the early morning and in the late afternoon. Mating behaviour was first seen after the initial feeding peak in the early morning and, whereas it was still apparent in the early afternoon, it declined again near the secondary peak of feeding activity at I700 hours, These findings were substantially confirmed by combining the data on feeding and mating activity obtained from all three study areas., The behaviour of four captive Indian Ocean bottlenose dolphins (Tursiops aduncus)-a bull, two cows (adult) and a female calf-was observed for a total of Io4.5 hours during regular 30 minute observation sessions, conducted on a random basis at all times of the day, between March and November, I970. Units of precopulatory and copulatory behaviour were defined and quantified together with concomitant whistle-phonation in relation to the time of day. The frequency of social interactions was significantly influenced by a diurnal cycle. Social behaviour was infrequent at night and in the early morning, but increased significantly to reach a peak at midday and in the early afternoon Whistle-phonation rarely occurred at night and was still infrequent in the early morning. The behavioural roles in courtship contexts were interchangable between age and sex classes and sexual partners adopted identical courtship display postures with equal frequency. Free-ranging bottlenose dolphins were studied in three areas along the eastern Cape coast: Algoa Bay (34°S.25°E.), the Tsitsikamma Coastal National Park (34°S.23°E.), and Plettenberg Bay (34°S. 23°E.) Bottlenose dolphins were sighted on 122 occasions and were observed for a total of 79.7 hours between Janary I970 and May I97I. A systematic watch during all daylight hours was maintained for dolphins during three seasonal field trips to Plettenberg Bay. The dolphins entered the Bay mainly in the early morning and in the late afternoon. Feeding procedures and co-ordinated herding of food-fish by schools of bottlenose dolphins was described. The units of social behaviour scored in captivity, including mating attempts by bulls, were also observable under free-ranging conditions. Feeding was most frequent in the early morning and in the late afternoon. Mating behaviour was first seen after the initial feeding peak in the early morning and, whereas it was still apparent in the early afternoon, it declined again near the secondary peak of feeding activity at I700 hours, These findings were substantially confirmed by combining the data on feeding and mating activity obtained from all three study areas.]