Science, Vol. 311, No. 5767. (17 March 2006), pp. 1613-1615.
Proc Biol Sci, Vol. 270, No. 1521. (22 June 2003), pp. 1271-1276.
J Exp Anal Behav, Vol. 63, No. 3. (May 1995), pp. 313-329.
Ecology, Vol. 68, No. 4. (1987), pp. 1104-1108.
Anim Behav, Vol. 53, No. 6. (June 1997), pp. 1129-1142.
Science, Vol. 253, No. 5023. (30 August 1991), pp. 980-986.
Nature, Vol. 377, No. 6551. (26 October 1995), pp. 725-728.
Anim Cogn, Vol. 10, No. 3. (July 2007), pp. 283-292.
J Exp Biol, Vol. 210, No. Pt 2. (15 January 2007), pp. 269-277.
Ecology, Vol. 61, No. 1. (1980), pp. 119-128.
PLoS Biol, Vol. 2, No. 12. (December 2004)
Proc Biol Sci, Vol. 271, No. 1556. (7 December 2004), pp. 2459-2465.
The American Naturalist, Vol. 100, No. 916. (1966), pp. 603-609.
Journal of Theoretical Biology, Vol. 175, No. 3. (07 August 1995), pp. 305-316.