Beyond mood: judgement bias is not associated with maternal aggression in canaries

Abstract Maternal aggression (MA) — offspring-directed aggression expressed by breeding females — occurs across diverse taxa, yet its proximate drivers remain poorly understood. One candidate mechanism is individual variation in affective state. Females in a more negative emotional disposition may show reduced tolerance to offspring demands, lowering the threshold for aggressive responses. We tested this hypothesis in breeding female canaries ( Serinus canaria ) using a cognitive judgement bias test (JBT), in which approach latency to an ambiguous stimulus served as a proxy for judgement bias. Females reliably discriminated between rewarded and unrewarded stimuli, validating the JBT. However, when accounting for individual differences in approach speed, the JBT score did not differ between MA and non-aggressive females. These results indicate that judgement bias, did not predict the subsequent expression of MA in this system, suggesting that offspring-directed aggression is not a direct consequence of a pessimistic affective disposition.