After moving to Bristol University, he collaborated with Professor K.R.L. Hall in establishing a centre for primate studies, extending socio-ecological principles to primates, supervising doctoral projects and leading field research in Ethiopia on geladas and in Morocco on the Barbary macaque, subsequently developed by Robin Dunbar and John Deag respectively.
His year as Fellow at the Center for Advanced Study in the Behavioral Sciences at Stanford University in California introduced him to the new techniques of humanistic psychotherapy. On return to Bristol, his students requested him to demonstrate these methods, leading to the creation of the Bristol Encounter Centre and to his teaching of the subject widely in the UK, especially based on workshops run at his retreat centre in mid Wales.
In 1977 Crook led an expedition to Zanskar in the Himalayas of Ladakh, a pilot study focussing on polyandry. For several years, he and colleagues led further expeditions studying the geology, agriculture, social and family life and monastic practices in this remote, high-altitude region. He later returned with James Low, a Tibetologist fluent in the texts and language, to study the lives of Buddhist hermits in the mountains.
Retiring early, he began practising Zen Buddhism in intensive retreats taught at Dharma Drum Retreat Center in New York by Chan Master Sheng-yen of Dharma Drum Mountain, Taiwan, who in 1993 transmitted to him the authority to teach Chan Buddhism. Forming the Western Chan Fellowship with colleagues, Crook developed a programme of retreats adapted to Western Zen practitioners.
He died on 15 July 2011, shortly after a gathering of many former students and colleagues in Somerset to celebrate his life. Dr Innes Cuthill, Professor of Behavioural Ecology at Bristol University, described him as "a pivotal figure in the rise of British primatology and socio-ecology".
^Crook, J.H. 1997. Hilltops of the Hong Kong Moon. Minerva.
^Crook, J.H. 1953. An observational study of the gulls of Southampton Water. British Birds 46: 386–397.
^Crook, J.H. 1964. The Evolution of Social organisation and Visual Communication in the Weaver Birds (Ploceinae). Behaviour Monograph. 10. Brill. Leiden.
^Lack, D. 1966. Population Studies of Birds. Clarendon. Oxford, quoting Crook, J.H. 1965. The adaptive significance of Avian Social organisations. Symp. Zool. Soc. Lond. 14: 181–218. Also Crook, J.H. 1970. Social organisation and the environment: aspects of contemporary Social Ethology. Animal Behaviour 18: 197–209.
^For example: Crook, J.H. and P. Butterfield. 1970. Gender role in the social system of Quelea. pp. 221–248. In Social behaviour in Birds and Mammals. J.H. Crook (Ed.). Academic. London.
^Crook, J.H. and J.S. Gartlan. 1966. Evolution of Primate Societies. Nature 210: 1200–1203.
^See: Crook, J.H. (Ed.) 1970. Social behaviour in Birds and Mammals: Essays on the Social Ethology of Animals and Man. Academic. London.
^Crook, J.H. and S. Crook. 1988. Tibetan polyandry: problems of adaptation and fitness. In: L. Betzig, M. Borgerhof Mulder and P. Turke (Eds). Human Reproductive Behaviour. Cambridge.
^Crook, J.H. and H. Osmaston (Eds.) Himalayan Buddhist Villages. Motilal Banarsidass, Delhi and Bristol University. 1994.
^Crook, J.H. 1995. Psychological processes in Cultural and Genetic Co-evolution. In: E. Jones and V. Reynolds (Eds.) Survival and Religion. Wiley. Crook. J.H. and J. Low. 1997. The Yogins of Ladakh: A Pilgrimage Among the Hermits of the Buddhist Himalayas. Motilal Banarsidass. Delhi.
^Li, R. (Ed.) 2002. Chan comes West. Dharma Drum Publications.
^Crook, J.H. 1980. The Evolution of Human Consciousness. Clarendon. Oxford.
^Crook, J.H. 2002. Illuminating Silence. Watkins. London. Crook, J.H. 2009. The Koans of Layman John. Lulu.