By 2050, 68% of the world’s 9.7 billion people will be residing in urban areas (United Nations (UN) Department of Economic Social Affairs, 2019a; United Nations (UN) Department of Economic Social Affairs, 2019b). As cities expand to accommodate more people, their impacts to ecosystem processes and biota increase. Urban areas present unique and dynamic challenges for resident wildlife (Lowry et al., 2013; Miranda et al., 2013; Alberti, 2015; Birnie-Gauvin et al., 2016). In response to anthropogenic stressors, urban wildlife may exhibit behaviors differently than their non-urban counterparts (Ditchkoff et al., 2006; Chapman et al., 2012; DeCandia et al., 2019).
As learning and behavioral adjustments are the primary ways animals cope with changing environments, the highly modified urban landscape provides a veritable proving ground for the ability of wildlife to adapt (Brown, 2012; Greggor et al., 2016).
Decreasing natural habitat—alongside increasing anthropogenic resources—can lead to behavioral shifts in urban wildlife populations that present unique management and conservation challenges (Riley et al., 2010; Bateman and Fleming, 2012; Magle et al., 2019).
Efforts to promote urban biodiversity while minimizing human-wildlife conflict will require a comprehensive understanding of what behavior changes are occurring in urban wildlife and how these species are potentially adapting over time.
Although behavior change can occur in wildlife without adaptation, it is helpful to consider behavioral responses, in terms of timescale and permanence, as either regulatory, acclimatory, or developmental (Lopez-Sepulcre and Kokko, 2012; McDonnell and Hahs, 2015).
Where behavior changes fall among these three categories of adaptative response can offer insight into the mechanisms of change and whether behaviors may revert to population norms or progress toward permanent adaptation (Dingemanse et al., 2010; McDonnell and Hahs, 2015).
Regulatory responses such as changes in alert behavior like harm avoidance or decreased flight initiation distance (FID) often develop within seconds to hours, whereas acclimation (e.g., adjustments in social structures and territoriality) may develop gradually over days and weeks (Bateman and Fleming, 2012; McDonnell and Hahs, 2015).
Physiological changes and behavioral syndromes such as neophilia and boldness may indicate more permanent developmental response potentially leading to evolutionary change (Dingemanse et al., 2010; Lopez-Sepulcre and Kokko, 2012; McDonnell and Hahs, 2015).
These adaptive responses may complement species survivability in some cases while being detrimental in others (Lopez-Sepulcre and Kokko, 2012; Lowry et al., 2013; Robertson, 2018; Ellington and Gehrt, 2019). As humans continue to alter the habitat and resources available to urban wildlife, knowing how these animals are adapting their behavior is key to understanding how certain species will persist in urban environments (Ryan and Partan, 2014; Soulsbury and White, 2015).
Despite urbanization’s significant impact on wildlife, urban wildlife research remains a young and poorly understood field (Birnie-Gauvin et al., 2016; Magle et al., 2019). In their review of urban wildlife research, Magle et al. (2012) found that urban wildlife studies comprised 2% of total publication volume. Although animal behavior is a common research topic and behavioral changes between urban and non-urban conspecifics are somewhat widely studied, mammals have been underrepresented (Magle et al., 2012; Miranda et al., 2013; McDonnell and Hahs, 2015; Schell, 2018).
This is somewhat surprising as changes in mammalian behavior can often be precursors to conflict with humans and understanding how mammals use urban areas is an important component of wildlife management (Gehrt and McGraw, 2007; Karelus et al., 2017).
Although selective urban pressures can have contrasting effects among mammalian species, it appears that behavioral flexibility among mammals allows them to better adapt to the urban environment (Santini et al., 2019).
Generally, mammals are easily disturbed by human activity which drive changes in their behavior that can impact diet, reproduction, stress levels, dial activity, and disease prevalence (Ditchkoff et al., 2006; Birnie-Gauvin et al., 2016).
These changes can lead to adaptations that may have important eco-evolutionary consequences. Despite the importance of understanding behavior changes in urban mammals, there has been no comprehensive review of the current primary literature specific to urban mammal behavior.