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Behavioural polymorphisms associated with morphs with a known genetic basis are interesting to study since they provide a model system to investigate the molecular basis of complex behaviours. White-throated sparrows are one of such rare models, presenting two morphologies and behavioural types, tan and white, caused by a chromosomal rearrangement. The behavioural differences have been mainly studied during reproduction, defining two morph-specific breeding strategies and different levels of aggression between morphs. Outside of the breeding season, the morphological differences are less apparent, morphs are more difficult to distinguish and the behavioural polymorphism is poorly understood. In this study, we caught wild individuals during the winter, determined their morph by genetic analysis, and analysed the differences in behaviour between morphs when encountering a novel object under standardized conditions in captivity. White morphs are more aggressive during reproduction; therefore, we expected them to be less affected by the presence of the novel object than tan morphs; animal personality research shows that more aggressive individuals are less affected by the presence of novel objects (i.e. neophilic). Contrary to our expectations, white morphs were more neophobic than tan morphs, and within morphs, males were more neophobic than females. Furthermore, white morph individuals and males of both morphs suffered greater weight loss during captivity compared to tan morphs and females, respectively, suggesting that the response to captivity-induced stress differs between morphs and between sexes. Finding behavioural differences between morphs not related to reproduction implies a broader impact of the effects of the chromosomal rearrangement on the behavioural polymorphism in this species.