Evidence of three distinct lactation stages in nursing gazelles: Implications on maternal behaviour assessment

Studying suckling behaviour has been used to understand parent-offspring conflict in mammals when the mother adjusts the amount of resources invested into an offspring during the lactation period. However, most studies report this information as a by-product of studying other types of suckling behaviour, like allosuckling. We aimed to understand this decision-making process by analysing the filial suckling bouts where the interval from the previous filial suckling bout was known. We used a captive population of threatened dorcas gazelles (Gazella dorcas) as a model species. Our findings showed that the lactation period in dorcas gazelle is characterised by three distinctive behavioural stages, where the behaviour of mother and calf changes rather fast, despite the progressive change in suckling duration. Early lactation (EL), when suckling bouts are always terminated by the calf; mid lactation (ML), when both the mother and the calf indistinctly may end up the suckling bouts; and late lactation (LL), when it is the mother who unfailingly ends lactation events. Also, we found evidence of male-biased maternal investment, as mothers tended to offer more investment towards male calves when suckling Additionally, we confirmed a compensational mechanism whereby calves born later in the birth season were suckled for longer (in terms of duration of suckling bouts) than calves born earlier, resulting in similar weaning dates for all studied calves. Therefore, many aspects may be overlooked if the influence of allosuckling on standard suckling is not considered when analysing suckling behaviour. Thus, we suggest this method of standard suckling behaviour analysis, where all behaviours which may alter the calves' demands and mothers' resources are removed (i.e., suckling attempts, allosuckling, and suckling after allosuckling).