The removal of pre-existing geographical barriers between species, notably by humans, allows previously isolated species to hybridize. Interspecies hybridization has been studied at different levels but the mother-young relationship, which is crucial for the offspring's survival, has not been investigated in large wild mammals. We compared the establishment of the mother-young relationship at birth and during the first week of life and the morphological development of the young in red deer, Cervus elaphus, sika deer, Cervus nippon, and their hybrids (male nippon x female elaphus). Most mother-young behaviours did not differ between the three groups, showing strong conservation of peripartum behaviours in cervids. In contrast, the behaviour and body size of the hybrid young were similar or tended to be close to those found in the maternal species, suggesting important maternal effects. In addition, hybrid young were more likely to be standing during the first week than young from the other groups, possibly resulting from increased maternal stimulation and/or hybrid vigour. Adult females in the herd were more likely to perform smell-related and agonistic behaviours towards the hybrid young, suggesting potential species recognition issues, which require further investigation. In conclusion, our findings show that hybridization has no noticeable impact on the mother-young relationship, which could partly explain the success of hybridization between the sika and red deer in the wild. (C) 2019 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.