Decreased vigilance or habituation to humans? Mechanisms on increased boldness in urban animals

Abstract

Increased boldness is one of the most prevalent behavioral modifications seen in urban animals and is thought to be a coping response to anthropogenic environmental alterations. Most previous studies have shown enhanced boldness manifested as changes in responses to humans approaching, such as reductions in flight initiation distance (FID). However, this includes two confounding factors related to “boldness,” that is, reduction of vigilance and habituation to humans. Confounding these totally different processes could lead to our misunderstanding of urban adaptation and how to properly manage urban wildlife. Here, we propose a simple framework to separate the two processes using two flight distance measures toward different approaching threats. We considered that the distance at which targeted individuals noticed an approaching object (i.e., alert distance, AD) was related to vigilance, whereas FID represented risk assessment, which is related to habituation. We applied a predictive framework using AD and FID to Eurasian red squirrels’ responses to multiple threats of different risk levels (i.e., humans, model predators, and novel objects). AD was shorter in urban individuals compared with rural ones but not different among the approaching objects. FID was shorter in urban individuals and also varied among the objects with the shortest FID toward humans, whereas rural individuals showed similar FID to the different objects. These results suggest that, although urban individuals showed reduced vigilance, they could still assess different risk levels. Our framework can easily be applied to many animals and could significantly improve our understanding of wild animals’ adaptations to urban environments.

Changes in the social behavior of urban animals: more aggression or tolerance?

“…Given the gap in this knowledge, mutually exclusive hypotheses describing this aspect of social behavior of urban animals can be formulated. The first hypothesis may assume that direct contacts between urban individuals are characterized by higher aggressiveness than in non-urban populations (which seems to be consistent with papers of Lacy and Martins 2003;Fokidis et al 2011;Tuomainen and Candolin 2011;Møller 2012;Lowry et al 2013;Miranda et al 2013;del Barco-Trillo 2018;Baxter-Gilbert and Whiting 2019;Uchida et al 2019). In turn, another hypothesis may assume that direct contacts between urban individuals are more tolerant compared to non-urban populations, since urban animals have access to anthropogenic food resources, and abundance of such food can reduce intra-population competition and the tendency towards monopolization of resources (Francis and Chadwick 2012;Oro et al 2013;Becker and Hall 2014;Thomas et al 2018…”

“…rufus, coyote Canis latrans, mule deer Odocoileus hemionus or wild boar Sus scrofa, the most common behavioral response is to adjust the circadian rhythm to avoid people (George and Crooks 2006;Podgórski et al 2013;Gaynor et al 2018). In the case of birds or mammals whose daytime patterns of activity coincides with the human activity, the avoidance of people is not temporal but spatial and is based on keeping a safe distance in space (Atwell et al 2012;Bateman and Fleming 2014;Cavalli et al 2018;Mikula et al 2018;Uchida et al 2019).…”

Habituation is not neutral or equal: Individual differences in tolerance suggest an overlooked personality trait

“…In recent literature, the FID ≤ alert distance/VOD ≤ SD relationship has been referred to as a “constrained envelope” and results in some underlying issues with analysis due to extreme heteroscedasticity breaking model analysis assumptions. Although other approaches have been suggested, e.g., quantile regression ( 56 ) and Phi index ( 36 ), we elected to control for varying SD indirectly by including one of the other independent distance measures, i.e., to standardize the analysis for variance in SD, we included VODD (as a covariate and as a random slope over individual identity) in all models analyzing VOD and VODI (as a covariate and as a random slope over individual identity) in all models analyzing FID ( 57 ). This allowed us to retain the covariate predictor variables in the analysis, which would not be possible with the Phi index.…”

Evolutionary dynamics in the Anthropocene: Life history and intensity of human contact shape antipredator responses

“…Such interventions may lead to both phenotypic modifications and evolutionary changes in a population. Animals surrounding cities or living close to villages and human habitation may become less wary towards humans but also less wary towards genuine predators [56]. Our data-driven conclusions go even further, showing that being in urbanized areas leads to a rate of phenotypic change that is apparently faster than that seen in captive animals that are intentionally isolated from predators.…”