Animals in cities are consistently bolder, more aggressive, more explorative and more active than their non-urban counterparts.
Boldness was observed to have the strongest increase in cities.
Urban environments may favour risk-taking individuals better able to tolerate humans, compete for scarce resources and navigate human-altered landscapes.
Animals living in urban areas are much bolder, more aggressive and more explorative compared to their non-urban counterparts, according to a new study.
The findings published in the Journal of Animal Ecology were based on an assessment of 133 species, including birds, mammals, amphibians, reptiles and insects. The authors accessed 80 studies to use phylogenetically controlled meta- analyses to examine urban-associated behavioural differences in wild animals, focusing on four behaviours — aggressiveness, boldness, exploration and activity.
“We found that urban populations were on average bolder, more aggressive, more explorative and more active relative to non-urban conspecifics, with boldness showing the strongest urban-associated increases. These findings were robust in avian species, which were well represented in the studies we reviewed — 72 per cent of all estimates. Conversely, among non-avian species — which were considerably less well represented across studies — boldness was the only behaviour that was significantly increased in urban populations, though non-avian urban populations tended to be more aggressive than their non-urban counterparts,” the study noted.
Urban-associated increases in behavioural traits occurred across species irrespective of ecological category. Some 84.2 per cent of the boldness data came from flight initiation distance (FID) studies, suggesting that urban animals have a much higher tolerance for human presence.
The analysts noted that urban environments may actively select for bolder and more aggressive individuals because these traits provide a competitive edge in navigating human-altered landscapes.
Several factors could contribute to this phenomenon, they wrote. “First, being bolder and taking more risks may increase an individual's likelihood of invading urban areas, either because bold individuals have a greater propensity for dispersal, either actively or passively; or because bolder animals prefer specific habitat characteristics that may be present in an urban environment.”
Alternatively, though not mutually exclusively, higher boldness may be an adaptive plastic or genetic response that increases the likelihood of settling or surviving in urban habitats. Increased boldness may give individuals a competitive edge in urban environments with limited or low- quality resources or changed predator communities. Bolder animals may also be less sensitive to human presence, the study showed.
These behavioural shifts were observed regardless of a species' ecological niche, dietary type, or whether they were considered "urban adapters" or “exploiters”.
While the trend toward bolder urban animals is clear, the analysts said that taxonomic imbalance and most studies (including this one) using a binary "urban vs nonurban" classification may be oversimplifying the complex gradients of city environments.
Addressing this gap will require experimental or longitudinal approaches that explicitly test for gene-based behavioural responses to urban pressures, the authors of the report concluded.