The balance between care and conflict may be key to understanding maternal aggression in canaries.

Parental care improves offspring quality and survival, thereby enhancing parental fitness. Yet, seemingly maladaptive parental behaviours such as directed aggression towards the offspring have been reported in a variety of species. While maternal aggression-defined as aggressive interactions from mothers to the offspring within the family context-may be a seemingly maladaptive behaviour, it could also be an adaptive strategy allowing optimal resource allocation for current and future reproduction in the face of evolutionary conflicts of interest. This study investigated associations between maternal aggression and altered offspring development in domestic canaries (Serinus canaria). Offspring exposed to maternal aggression showed reduced growth, while no differences in survival were observed. In addition, juvenile males, but not females, exposed to maternal aggression displayed increased threatening behaviours, highlighting the importance of considering long-term effects when interpreting the significance of aggressive parenting styles. Females that exhibited maternal aggression did not lay larger second clutches, as would be expected if aggression during the first reproductive event was directed at prioritising future reproduction. However, they laid larger and less variable clutches overall, suggesting that females that engaged in maternal aggression may be less flexible and more prone to high investment at egg laying.