As cities expand across the globe, understanding factors that underlie variation in
urban tolerance is vital for predicting changes in patterns of biodiversity. Endocrine
traits, like circulating hormone concentrations and regulation of endocrine responses,
might contribute to variation in species' ability to cope with urban challenges. For
example, variation in glucocorticoid and androgen concentrations has been linked to
life-history and behavioural traits that are associated with urban tolerance. However,
we lack an understanding of the degree to which evolved differences in endocrine traits
predict variation in urban tolerance across species. We analysed 1391 estimates of
circulating baseline corticosterone, stress-induced corticosterone, and testosterone
concentrations paired with citizen-science-derived urban occurrence scores in a broad
comparative analysis of endocrine phenotypes across 71 bird species that differ in
their occurrence in urban habitats. Our results reveal context-dependent links between
baseline corticosterone and urban tolerance, as well as testosterone and urban tolerance.
Stress-induced corticosterone was not related to urban tolerance. These findings suggest
that some endocrine phenotypes contribute to a species’ tolerance of urban habitats,
but also indicate that other aspects of the endocrine phenotype, such as the ability
to appropriately attenuate responses to urban challenges, might be important for success
in cities.
