Sentinel behaviour and urban environments: A corvid’s perspective

Abstract

American crows (Corvus brachyrhynchos) are the black-clad rulers of a city’s skies and can be spotted in most North American cities. The abundance of corvids has increased with increasing urbanization, suggesting they benefit from living near humans. Recent literature shows that urbanized species such as the American crow can behaviourally adapt to exploit anthropogenic resources resulting in positive urbanization effects on corvids. While individual-level behavioural adaptations are an active area of research, social behaviour adaptations and their contribution to the success of urbanized species are underexplored. Sentinel behaviour is a social behaviour that could increase a species' survival of group members. Using a scoping review approach, several intrinsic (or internal, e.g. sex or body mass) and extrinsic (or external, e.g. predation risk or anthropogenic noise) factors that can alter the sentinel behaviour of mammal and avian species were identified. Factors that alter an individual’s energetic resources can greatly affect an individual’s ability to perform sentinel behaviour, and factors that increase risk to the individual will increase an individual’s propensity to perform the behaviour. During the summer of 2022, I observed the foraging behaviour of American crows in the presence and absence of a sentinel and in the green and commercial areas of St. Catharines. I found that American crows altered their social foraging behaviour in different urban microenvironments but had fewer significant changes in response to the presence of a sentinel. I found a significant interaction between sentinel presence and generalized environment on the behaviour of foragers, suggesting increased reliance on the sentinel when sentinel behaviour is most effective: in green spaces. My findings highlight the need to consider both intrinsic and extrinsic factors and their interaction when studying social behaviours. My findings highlight the need to continue studying the effects of urbanization on social behaviours. By doing so, future studies could unearth the complex mechanisms behind the evolution of social behaviours and help predict how they could change in an ever-urbanizing future.