1. Chimpanzees of the Gombe Stream Reserve, pp 425-473 in In Primate Behavior. ed. New York, Holt, Rinehart and Winston, 1965.
2. Great apes in captivity: The good, the bad, and the ugly, pp. 239-272 in Captivity and Behavior. ; ; eds. New York, Van Nostrand Reinhold Co., 1979.
3. Behavioral Enrichment in the Zoo. New York, Van Nostrand Reinhold Co., 1982.
4. Tool use by captive chimpanzees at an artificial termite mound