The impact of urbanisation on social behaviour: a comprehensive review

Urbanisation is a key driver of global environmental change and presents animals with novel stressors and challenges. It can fundamentally influence social behaviour and has the potential to reshape within- and between-species social interactions. Given the role of social behaviour in reproductive fitness and survival, understanding how social interactions change in response to urban conditions is crucial in addressing individual-, population-, and species-level responses to urbanisation, as well as the consequential ecological impacts. Here, we conducted the first systematic review addressing the impact of urbanisation on social systems and interspecific interactions. We synthesise the outcomes of the 227 studies from our literature search, organised across three key topics: (i) effects of urban stressors on social behaviour (N = 170), (ii) social system responses to urban environments (N = 75), and (iii) the impact of urbanisation on interspecific interactions (N = 12). Our review revealed that urbanisation is having a substantial impact on multiple facets of social behaviour, with 92% of studies finding a significant impact. We also identified several biases and gaps in the current literature. For example, 62% of all studies were conducted on birds, and 85% of studies testing urban stressors focused on anthropogenic noise. Given the diversity of animal social systems, there is obvious variation in social responses to urban conditions. However, we offer predictions for how social systems might change as urban environments continue to expand rapidly and suggest guidelines for future research to enhance generalisations across taxa. Our review brings together multiple areas of research, provides timely insights and outlines a framework for a unified and proactive approach to addressing social responses to urbanisation. This represents an essential foundation for anticipating species' responses to urban expansion and guiding effective conservation efforts.