9Ahsan M F. 200 1. Socio-ecology of the hoolock gibbon (Hylobates hoolock) in two forests of Bangladesh. In: The Apes: Challenges for the 21 st Century. Conference Proceedings. Brookfield: Chicago Zoological Society, 286 - 299.
10Altmann J. 1974. Observational study of behavior: sampling methods. Behaviour, 49 (3/4): 227 - 267.