Maternal deprivation and the development of stereotypic behaviour

Many farm, laboratory, zoo and companion animals experience some form of maternal deprivation. This is typically via separation from their mothers earlier than would happen in free-living populations, in some cases even while young are still dependent upon milk. Maternal deprivation may also occur in a qualitative way, via inadequate maternal care, perhaps caused by inexperience or by restrictive environments that limit maternal behaviours. In this paper we review evidence on the link between early separation from the mother and abnormal behaviour from a wide range of sources, including the early primate studies in this field, more recent examples from zoo and commercially reared animals, and human examples from studies of institutionalised children. We discuss factors that seem to influence the magnitude of later effects, such as developmental stage and age at separation, and whether separation is gradual (i.e. more similar to natural separation) or abrupt (as often the case in captivity). In these instances, however, maternal deprivation is just one aspect of a suite of changes that occur when infants are separated from their mothers. In the second part of the paper we therefore review the few cases where maternal loss per se has been investigated, and studies showing lasting affects of qualitative aspects of maternal care. We then look at the possible mechanisms underlying maternal deprivation-induced stereotypic behaviours including potential frustration of specific motivations, and lasting, more pervasive changes for instance in temperament or motor control. Finally, we discuss the practical and welfare implications of the effects of maternal deprivation, and suggest some topics for future research.