Social influences on the amount of food eaten by Norway rats.

A naive observer Norway rat offered a choice between two foods, after it interacts with a demonstrator rat fed one of those foods, increases its preference for whichever food the demonstrator rat ate. It is not known whether interaction with a demonstrator rat would also increase the amount that an observer rat would eat if it were given access only to the food the demonstrator had eaten. In this study, each observer rat interacted with a demonstrator rat fed a food, either familiar or unfamiliar to the observer, and the observer was then offered a weighed sample of the food that the demonstrator had eaten. It was found that, during the first hour of testing, observer rats that had interacted with demonstrators fed an unfamiliar food, increased their intake of that food roughly four-fold. Observer rats that interacted with demonstrator rats fed a familiar food however, did not increase their food intake. Socially enhanced intake of unfamiliar food was seen only during the first hour that observers had access to food and was compensated for during the next 23 h of feeding. This short-term increase in observer intake of unfamiliar foods appeared to result from socially-induced motivation to ingest unfamiliar foods rather than from socially-induced reduction in neophobia.