Species differences in preference to work for food rewards deliv-ered with predictable or unpredictable delays

F.H. de Jonge¹, K. Van de Put¹, J. Duit¹, R. Maes² and B.M. Spruijt¹

¹Ethology and Welfare Group, Dept of Animals, Science and Society, Veterinary Faculty, University of Utrecht, The Netherlands
²Biological Psychology, Nijmegen University, Nijmegen, the Netherlands

It was shown in birds and insects that animals may prefer to work for a food reward which is delivered with an unpredictable and/or variable delay rather than for food rewards delivered with a predictable delay (‘risk-sensitive foraging’). According to theoretical models, risk-sensitive behaviour will depend on the biology of the animal and will be predicted by the relationship between energy reserves and reproductive success. However, it is not yet known whether risk-sensitive behavior may be observed in mammals too.

In the present experiment, dogs, goats and pigs were trained to manipulate two levers in order to earn food rewards on a fixed interval schedule of 10 seconds. Subsequently, they were trained to manipulate one of the two levers in order to earn food rewards delivered with a predictable 10 seconds delay (lever 1), while manipulation of the alternative lever was rewarded with an unpredictable, randomly varied delay of either 4 or 16 seconds (lever 2). The total amount of rewards earned under either schedule was (on average) the same. Finally, the animal’s preference for a predictable versus an unpredictable delay was tested in ‘choice trials’ in which both levers were avaiable. A preferred option was defined by a 80% preferred responding during 5 consecutive trials.

Preliminary analysis of the results in both goats and dogs revealed that one third of the animals developed a preference for the predictable option, one third developed a preference for the unpredictable option and one third had no preference for either option. The results of the pigs are currently being analyzed.

Paper presented at Measuring Behavior 2005 , 5^th International Conference on Methods and Techniques in Behavioral Research, 30 August - 2 September 2005, Wageningen, The Netherlands.

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