Previous studies have emphasized the behavioural plasticity of successful urban wildlife species. In this study,

we emphasize the importance of disturbance monitoring by successful urban exploiters, Metformin cell line allowing them to vary their behavioural responses according to the level of risk to which they are exposed. Cities are challenging environments for many species of wildlife, presenting a loss of natural resources (i.e. habitat and food) and high levels of anthropogenic disturbance, that is pedestrian traffic, vehicular traffic and industrial noise (Lowry, Lill & Wong, 2012). Despite this, some species do extremely well in urban environments. Successful ‘urban adapters’ (sensu McKinney, 2006) are generally species that show high levels of opportunistic behaviour (i.e. are habitat or trophic generalists and can exploit novel niches; Bateman & Fleming, 2012, Lowry et al., 2012), or, in the case of birds, are also more gregarious or sedentary (Kark et al., 2007) or have large breeding ranges, high fecundity, dispersal and survival (Møller, 2008). Behavioural flexibility

and adaptive adjustments are therefore identified as a feature of successful urban species and are likely to be important in facilitating resource use, avoiding disturbance and enhancing communication (Slabbekoorn & Peet, 2003; Patricelli Napabucasin mouse & Blickley, 2006; Baker et al., 2007; Evans, Boudreau & Hyman, 2010; Lowry et al., 2012; Sol, Lapiedra & Gonzalez-Lagos, 2013). A major aspect of behavioural flexibility in urban adapters is how such animals are able to modify their antipredator medchemexpress behaviour towards humans, which may be regarded as ‘predation-free predators’ (Beale & Monaghan, 2004). Models of optimal escape theory predict that individuals should flee when costs of staying outweigh costs of flight, based on the variables of risk posed by the predator,

the cost of fleeing, the potential to rely on other defensive tactics, and the size of the prey group (i.e. increased vigilance and predator dilution) (Ydenberg & Dill, 1986; Cooper & Frederick, 2007). Animals should, therefore, assess the degree of risk represented and dynamically adjust their antipredator behaviour accordingly. In urban environments, where there is a high level of background disturbance, the success of urban wildlife may rely on their abilities to clearly distinguish between genuinely threatening and non-threatening stimuli and become habituated to some human activity. Although animals still need to be sensitive to the level of threat because of human presence, living without fear in the vicinity of humans is identified as a key behavioural trait of urban adapters (Kark et al., 2007).