Causation of the ontogenetic development of stereotypic digging in gerbils

To determine the factors that cause the development of stereotypic digging, features in the captive environment of young Mongolian gerbils,Meriones unguiculatus, were varied. It was hypothesized that stereotypic digging develops because stimuli that control digging motivation are lacking. A regulatory model of motivation was used to examine whether digging motivation is decreased by the performance of the motor pattern ‘digging’ or by the consequences of digging. Young gerbils that could dig in a sand area developed stereotypic digging. In contrast, young gerbils that could not dig in sand but had access to an artifical burrow, which was presumed to be the consequence of digging, showed less non-stereotypic digging than gerbils from the sand treatment and did not develop stereotypic digging. Therefore, the mere perception of the stimulus ‘burrow’ by a retreating animal decreased digging motivation. The complexity of the artifical burrow was reduced to a few elements to analyse in detail the stimuli that control digging motivation. A dark and narrow chamber at the end of a tube connected to the cage provided the stimuli that elicited retreating and prevented the development of stereotypic digging. The tube was a necessary feature: a chamber alone did not prevent the development of stereotypic digging. Such a stimulus situation seems to match the stimuli of a natural burrow which is built to buffer climatic fluctuations and to provide shelter from predators. The results show that stereotypic digging develops when a young gerbil cannot achieve a stimulus situation that is efficient in decreasing digging motivation.