Further experimental analysis of the social learning and transmission of foraging information amongst Norway rats.

Adult male Norway rats were tested to see if their foraging efficiency could be improved by social learning and to investigate whether foraging information could be socially transmitted along a chain of animals. In Experiment 1, 'observers' were placed in one of four conditions, distinguished by the nature of their experience during an observation phase, in which they either observed: (1) a trained conspecific unearthing buried carrot; (2) a trained conspecific digging; (3) carrot pieces only; or (4) an empty enclosure (the control group). When tested 24 h later it was found that subjects in group 1 alone exhibited a significantly elevated foraging ability relative to the control group, being more active, and unearthing more carrot pieces in total. The results show that perception of a trained demonstrator conspecific successfully foraging for food is necessary for social learning of foraging information to occur, probably by a local enhancement mechanism. In Experiment 2, chains of transmission were established by allowing each observer to act 24 h later as the demonstrator for the next observer. In one of two transmission groups subjects were given an extra period of individual foraging experience in the test enclosure, with no demonstrator present. Enhanced levels of foraging efficiency were maintained across eight transmission episodes for both transmission groups relative to a no-transmission control. Subjects in the group with the additional experience unearthed significantly more buried food than subjects in the other transmission group. The experiments extend our standard transmission group was upheld. The superior performance of demonstrators in this group, as reflected in their higher level of carrot digging, suggests that the extra period of experience did indeed enhance their ability to act as effective demonstrators. The elevated performance of subjects in this group is attributed to a combination of social and individual learning. This finding suggests that the stability of social transmission may, under some circumstances, be bolstered by individual reinforcement of socially learned and enhanced patterns of behaviour. It also lends support to the hypothesis, proposed to account for the findings of our earlier study, that motivational factors such as fatigue, may detract from subjects' performance as demonstrators when this demonstration follows closely after the additional period of individual experience, but that a 24 h period is sufficient to allow such motivational factors to decay. If individual experience can buttress socially learned traits then this interaction may act so as to prolong the period of time that a socially transmitted trait remains in a population. It is conceivable that an additional period of foraging longer than 10 min may further enhance subjects' subsequent performance as demonstrators. The complex relationship between individual and social learning has received little attention. It is not clear how, if at all, social learning is different from other forms of learning (Plotkin, 1988), apart from the obvious requirement that another animal somehow be involved in the social learning process. Boyd and Richerson (1985) argue that social and individual learning are, at least in humans, alternative ways of acquiring a particular behavioural variant. Most recent studies of animal social learning, on the other hand, tend to emphasize the stimulus enhancing role of the demonstrator animal (Galef, 1988a), thereby suggesting that social learning is a sub-category of individual learning. This study shows that individual learning can reinforce the acquisition and expression of socially acquired behavioural variants.