Egg-Eating Behaviour in Laboratory Squirrel Monkeys (Saimiri scuireus)

Abstract

The present study aimed to clarify an individual character of squirrel monkey by analysing a complicated behaviour, the egg-eating behaviour series (ES), of laboratory-reared squirrel monkeys. Eight types of unit movements were observed in the ES: the initial taking of the egg by hand; rolling it between the fingers; sniffing it in its shell; biting it in its shell; pressing or rubbing it against a surface of the cage; opening or peeling it; eating it; or putting it down without eating. In the first experiment, the behaviour of 72 monkeys was recorded by direct observation or by a video camera, following which the sequences of the movement from a total of 378 ES were analysed. Three statistically significant ES were detected (Ta-Bi-Op/Pe-Ea, Ta-Ro-Bi-Op/Pe-Ea and Ta-Pr/Ru-Bi-Op/Pe-Ea). In the second experiment, eight squirrel monkeys were selected at random from the same group and 31 to 36 ES for each monkey were observed and analysed. These monkeys were classified into a pressing/rubbing (Pr/Ru) group and a no-Pr/Ru group. Pr/Ru appeared to have no relationship to the monkey's age or sex. Furthermore, the Pr/Ru group monkeys contained individuals always exhibiting Pr/Ru in their ES and others sometimes lacking Pr/Pu in their ES. In short, the monkeys could be divided into two groups (ie., Pr/Ru and no-Pr/Ru) and they displayed their own individual characteristic ES. We concluded that the ES observed in this experiment suggest that the squirrel monkeys acquired individual characteristics in their ES in the laboratory environment.