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 animals 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
, 5th International Conference on Methods and Techniques
in Behavioral Research, 30 August - 2 September 2005, Wageningen, The
Netherlands.
© 2005 Noldus
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