Chronobiologische Untersuchungen zur Raum-Zeit-Nutzung bei einem Orang-Utan-Paar im Zoo Osnabrück

Research about influences of natural and artificial environmental influences to animal behaviour is essential for the improvement of animal welfare in zoos and can be of importance for the conservation of free living animal populations. In literature on Orang-Utans (Pongo spec.), the biggest and heaviest of arboreal mammals, a connection between solar altitude and circadian rhythm was found. Activity during the waking hours was additionally influenced by weather, food supply, intra- and interspecific influences. Sunset marked the end of daily activity and the animals showed their anticipation among other things in the daily construction of tree nests.An examination of artificial influences, Orang-Utans in everyday zoo life are exposed to, is starting point for the present study. Further intentions were to record the activity patterns of two adult Zoo-Orang-Utans from evening to morning and gather information about nest building and the dominance situation between the two animals. During six weeks the Orang-Utan couple Buschi and Astrid (1.1) in the Zoo of Osnabrück was observed in the indoor enclosures every day from evening to morning via a video surveillance system (hours of observation: 623.5 h (Buschi, male); 236.5 h (Astrid, female)).The activity profiles of Buschi and Astrid fit into the results of field studies concerning chronobiological organisation and activity pattern. In the afternoon both animals were quite active and fed, afterwards they constructed their nests and laid down on them. The present observation leads to the conclusion that both, sunlight as well as the artificial lights, are able to influence their behaviour as so-called zeitgebers. Every night Buschi's sleep was interrupted several times by short active phases, in which he scratched himself extensively and adjusted his nest. Until this observation no comparable data concerning comfort activity by night in field and zoo situations was available.Nest building behaviour similar to free living Orang-Utans has been shown by Buschi and Astrid as well, changes being dependant on available material and the lack of necessity for safety and stability. The behaviour of Buschi taking nest parts from Astrid, suggests dominance between the mates and the nest as a reason for competition.