Laura Gervais, Megan Thompson, Pierre de Villemereuil, Tracy Burkhard, Céline Teplitsky, Barbara Agathe Class, Denis Réale, anne charmantier

Urbanization is occurring globally at an unprecedented rate and, despite the eco-evolutionary importance of individual variation, we still have limited insight on how phenotypic variation is modified by anthropogenic environmental change. Urbanization can increase individual differences in some contexts, but whether this is generalizable to behavioral traits, which directly affect how organisms interact with and respond to environmental variation, is not well known. Here we examine variation across three behavioral traits linked to stress reactivity, anti-predator response, and novelty-coping (breath rate, handling aggression, and exploration behavior) in great tits Parus major along an urbanization gradient. We phenotyped > 1000 phenotyped individuals across nine years, to test whether individual differences in behavior increased with urbanization and spatial environmental heterogeneity. We used two different approaches: a city vs. forest comparison (i.e., a binary descriptor) and an urbanization gradient approach (i.e., a continuous quantitative score from 0 to 1) to explore the influence of impervious surface at different spatial scales. Our results suggested that urban individuals displayed more diverse stress-related and anti-predator behaviors (breath rate and handling aggression), yet showed more similarity in their exploratory behavior than forest counterparts. However, only individual variation in exploration changed along the urbanization gradient, with individual differences in exploration decreasing with increasing impervious surface area. Our results suggest that generalizations about how behavioral traits respond to urbanization will differ across behavioral dimensions. We may expect decreased individual diversity in urban birds for traits related to behavioral response to novelty.