A historical perspective on recent studies of social learning about foods by Norway rats

Early naturalists explained field observations of social influences on animal learning in terms of spoken language, deliberate tuition of one animal by another, or intentional imitation. During the first half of the present century, experimental psychologists analyzed instances of social learning by animals in laboratory tasks as special cases of operant or classical conditioning. Neither of these traditional approaches provided much insight into the complex processes that often support animal social learning. By combining ethological focus on social learning as it occurs in natural habitat with analytical techniques developed in the psychological laboratory, contemporary researchers have made considerable progress in describing the many ways in which social interactions influence behavioural development in animals. The author's investigations of social influences on food selection by Norway rats provide one example of such an ethopsychological approach to the study of animal social learning.     

Demonstration of a socially transmitted flavor aversion in rats? Kuan and Colwill (1997) revisited

In each of three experiments that differed only in procedural detail, observer rats interacted with pairs of conspecific demonstrators, one fed a cocoa-flavored diet (Diet Coc) and the other a cinnamon-flavored diet (Diet Cin). Immediately after both members of a pair of demonstrators had been fed, and 5 min before they interacted with an observer or observers, one of the demonstrators was made ill by intraperitoneal injection with lithium chloride. After interacting with a pair of demonstrators for 15 min, each observer was allowed to choose between Diet Cin and Diet Coc for 22 h. In all three experiments, observer rats consumed as much Diet Cin after interacting simultaneously with both an ill demonstrator that had eaten Diet Cin and a healthy demonstrator that had eaten Diet Coc as after interacting simultaneously with both a healthy demonstrator that had eaten Diet Cin and an ill demonstrator that had eaten Diet Coc. These results raise questions about the generality of Kuan and Colwill’s (1997) demonstration of socially transmitted flavor aversions in Norway rats.     

Female Japanese quail (Coturnix japonica) mated with males that harassed them are unlikely to lay fertilized eggs

Results of previous studies of courtship and mating in Japanese quail (Coturnix japonica) suggest that females avoid conspecific males because, while courting and mating, males engage in behaviors that are potentially injurious to females. However, prior experiments provided no direct evidence that females avoided harassing males. Here the authors show that a female quail choosing between a previous sex partner and an unfamiliar male avoids the former if he engaged in relatively many potentially injurious acts while courting and mating, (Experiments 1 and 2) and that males behaving aggressively toward mates are less likely than are gentler males to fertilize the females' eggs (Experiment 3). Male sexual harassment appears to be a tactic both aversive to female quail and relatively ineffective in fertilizing them.     

CAN IMITATION IN PIGEONS BE EXPLAINED BY LOCAL ENHANCEMENT TOGETHER WITH TRIAL-AND-ERROR LEARNING?

Abstract— Zentall Sultan and Sherburne (1996) reported that pigeons observing a conspecific demonstrator either step on or peck at a treadle to obtain food subsequently showed a significant tendency to manipulate the treadle as had their demonstrator. Zentall et al suggested this finding showed observer pigeons had learned by imitation to peck at or step on the treadle. However, the same result might have been obtained of pigeons had learned to step on the treadle by trial and error, and pigeons exposed to a treadle-pecking demonstrator had come to peck at the treadle as a result of nonimitative social learning processes such as local enhancement or contagion. Here we report the results for two control groups showing that pigeons do not learn to step on or peck at a treadle for food reward unless they observe a relevant demonstrator. These results considerably strengthen the original conclusion. Future research using the two action method to demonstrate imitative learning should include similar controls.     

Responses of observer rats (Rattus norvegicus) to complex, diet-related signals emitted by demonstrator rats

We explored the effects of complex, food-identifying signals emitted by demonstrator Long-Evans rats (Rattus norvegicus) on food preferences of their observers. In Experiments 1 and 2, observers identified each of 2 or 3 foods their demonstrators had eaten before interacting with observers. In Experiment 3, individual observers interacted with groups of demonstrators. Some of these demonstrators had eaten one food, some another. Observers then chose between the two foods. The greater the proportion of demonstrators in a group that had eaten a diet, the greater the proportion of that diet the observers ate. In Experiment 4, each observer interacted over several weeks with a series of demonstrators and preferred each of the foods its demonstrators had eaten. In sum, the food preferences of observers were affected by several different types of complex, food-identifying signals like those one might expect rats to encounter outside the laboratory.     

A failure to find socially mediated taste aversion learning in Norway rats (R. norvegicus)

Observer rats interacted with conspecific demonstrators immediately after demonstrators ate a novel diet and were made ill by LiCl injection. Following their interaction with demonstrators, observers were tested for aversion to their ill demonstrator's diet. Previous research has shown that (a) an observer can extract information from a demonstrator sufficient to permit identification of the demonstrator's diet (Galef & Wigmore, 1983) and (b) a rat ill from LiCl toxicosis is an adequate unconditioned stimulus in a taste aversion learning paradigm (Lavin, Freise, & Coombes, 1980). Further, two of the present experiments demonstrated that cues emitted by a rat, reflecting the particular diet it has eaten, are an adequate conditional stimulus in a toxicosis-induced aversion learning situation. Observer avoidance of a diet previously ingested by an ill demonstrator was, however, not demonstrated. The implications of the failure to find socially mediated aversion learning are discussed.     

A contrarian view of the wisdom of the body as it relates to dietary self-selection

The history of studies of dietary self-selection in cafeteria-feeding situations is reviewed briefly. The evidence is not consistent with the view that replete animals can reliably compose a nutritionally adequate diet from an array of food in a cafeteria situation. Similarly, the evidence is not consistent with the view that when deficient in a nutrient (excepting the case of sodium and, perhaps, of phosporus), animals can reliably select a nutritionally adequate diet when it is present among several deficient diets. General acceptance of the view that omnivores can easily self-select nutritionally adequate diet is attributed both to overreliance on theory and to lack of critical attention to data. The adequacy of functional arguments suggesting that omnivores must be able to self-select nutritionally adequate diets is questioned.