Fostering as a conservation breeding tool: Lessons from three case studies in the critically endangered European mink ( <i>Mustela lutreola</i> )

In conservation breeding programs offspring may become orphaned or require additional care to survive. Fostering represents a potential intervention to avoid the behavioral and physiological problems caused by human hand-rearing. We report five fostering events following the maternal loss of three litters (total of ten kits) in the critically endangered European mink. In two of these cases, we analyzed the dams' and kits' behavior during the first week after the fostering event and recorded the kits' weight. Three fostering events were successful, with foster kits surviving until weaning age; two were unsuccessful, possibly due to the age and developmental stage difference between foster and biological kits. Behaviorally, dams appeared to care for all kits equally, without differences observed in average maternal behaviors or aggression between dams and kits, or among kits. Despite the weight being difference between foster and biological kits, we have verified that fostering can be successful in this species. Future fostering attempts should complement behavioral observations with physiological parameters to assess effects on growth and survival and match foster kits with similarly aged litters to maximize chances of acceptance.