1. Zentall, T. R. & Galef, B. G. (eds) Social Learning. Psychological and Biological Perspectives (Lawrence Erlbaum Associates, London, 1998).
2. Shettleworth, S. J. in Behavioral Brain Research in Naturalistic and Semi-naturalistic Settings (eds Alleva, E., Fasolo, A., Lipp, H.-P. & Nadel, L.) 158–179 (Kluwer Academic, The Hague, 1995).
3. Vander Wall, S. B. Food Hoarding in Animals (Univ. Chicago Press, Chicago, 1990).
4. Clarkson, K., Eden, S. F., Sutherland, W. J. & Houston, A. I. Density dependence and magpie food hoarding. J. Anim. Ecol. 55, 111–121 (1986).
5. Gibb, J. A. Populations of tits and goldcrests and their food supply in pine populations. Ibis 102, 163–208 (1960).