Contribution to the study of behavioural development of free ranging white-handed gibbons (Hylobates lar) in the national park of Khao Yai, Thailand

Résumé

This study is a contribution to the general knowledge of behavioural development of Hylobates lar (White-Handed Gibbon). 5 social groups free-ranging in the National park of Khao Yai (Thailand) were followed from the 17th of March 2003 to the 20th of June
2003 for a total period of 73 days of observation. The main objective was to describe, quantify and measure various parameters relevant to the youngsters' behavioural development stages, from infant to juvenile. These parameters are the distance to the female; the clinging, suckling, playing and grooming behaviours; and the influence of the female's activity on the youngster's behaviour. Additionally, data were also colJected in contribution to an ongoing long term study of the habituated groups of White-handed gibbons of the park. 6 individuals (4 infants and 2 juveniles) were chosen from three different age categories (age class I, Il, and IV - 2 individuals of each age class), and followed daily during the whole activity period of the gibbons, from the night tree of the morning to the entrance into a new night tree in the evening. Data were collected using two simultaneous sampling methods. A one day focal sampling was used to collect data on the youngsters with a particular interest in the contact between infant and female. 5 minutes scan samplings were done ail along the day which allowed collection of data on ail the individuals of each group. In addition, in order to obtain mean durations of behaviours particularly relevant to the behavioural development of youngsters, a third sampling method was used: Instantaneous sampling data were coUected for the suckling, playing, and grooming behaviours. As predicted: With age, the infant/female bond weakens and therefore, suckling, and clinging decrease; whiles the mean distance to the female, grooming and playing increase with the development stages. On the contrary, no effect was demonstrated concerning a possible influence of the composition of the group on the social developrnent of the youngsters. With more data collection on the other developrnent stages and on larger sarnples of individuals, these pararneters could be more accurately defined and used as markers of developrnent stages for young free-ranging white-handed gibbons.

la date de réponse	2004
langue originale	Anglais
Superviseur	Michel MERCIER (Promoteur) & Marie-Claude Huynen (Copromoteur)