Do stereotypies help or harm? Exploring the link between cortisol level and abnormal behaviours in animals: a review

Stereotypical behaviours in animals, often linked to stress, are repetitive actions that may lack a clear purpose. This review examines the relationship between cortisol levels, a key stress hormone, and stereotypic behaviour across various animal species, including zoo mammals, horses, and dogs. A total of 99 studies were analysed to understand whether elevated cortisol levels are associated with stereotypies. While many studies report a positive correlation between cortisol and stereotypical behaviour, more detailed research suggests that these behaviours may also serve as coping mechanisms, potentially reducing cortisol levels. The findings highlight the complexity of this relationship, as some studies show a negative or no correlation at all. To address these inconsistencies, this review critically examines the existing evidence and aims to provide a clearer understanding of the relationship. The review emphasises the need for further research, including long-term studies and the inclusion of additional hormonal markers, to clarify whether stereotypical behaviours only reflect chronic stress or also represent stress-relieving adaptive responses.