1. McFarland, D. J. in Advances in the Study of Animal Behaviour Vol. 5 (eds Lehrman, D. S., Hinde, R. H. & Shaw, E.) 201–225 (Academic, London, 1974).
2. Tinbergen, N. E. Q. Rev. Biol. 27, 1–32 (1952).
3. Hinde, R. A. Animal Behaviour: a Synthesis of Ethology and Comparative Psychology (McGraw-Hill, New York, 1966).
4. Lindvall, O. & Bjorklund, A. in Handbook of Psychopharmacology Vol. 9 (eds Iversen, L. L., Iversen, S. D. & Snyder, S. H.) 139–231 (Plenum, New York, 1978).
5. Fallon, J. H. & Moore, R. Y. J. comp. Neurol. 180, 545–580 (1978).