The Geography of Fear: A Latitudinal Gradient in Anti-Predator Escape Distances of Birds across Europe

Abstract

All animals flee from potential predators, and the distance at which this happens is optimized so the benefits from staying are balanced against the costs of flight. Because predator diversity and abundance decreases with increasing latitude, and differs between rural and urban areas, we should expect escape distance when a predator approached the individual to decrease with latitude and depend on urbanization. We measured the distance at which individual birds fled (flight initiation distance, FID, which represents a reliable and previously validated surrogate measure of response to predation risk) following a standardized protocol in nine pairs of rural and urban sites along a ca. 3000 km gradient from Southern Spain to Northern Finland during the breeding seasons 2009–2010. Raptor abundance was estimated by means of standard point counts at the same sites where FID information was recorded. Data on body mass and phylogenetic relationships among bird species sampled were extracted from the literature. An analysis of 12,495 flight distances of 714 populations of 159 species showed that mean FID decreased with increasing latitude after accounting for body size and phylogenetic effects. This decrease was paralleled by a similar cline in an index of the abundance of raptors. Urban populations had consistently shorter FIDs, supporting previous findings. The difference between rural and urban habitats decreased with increasing latitude, also paralleling raptor abundance trends. Overall, the latitudinal gradient in bird fear was explained by raptor abundance gradients, with additional small effects of latitude and intermediate effects of habitat. This study provides the first empirical documentation of a latitudinal trend in anti-predator behavior, which correlated positively with a similar trend in the abundance of predators.

Factors affecting escape distance in birds

“…To check for nonrandom variation in FID and FFD across species, we ran a one-way analysis of variance with log-10 transformed data (DÍAZ et al 2013). We used a linear regression analysis to check for the effect of body mass on the FID and FFD (using means of FID and FFD of all individuals of the same species) and on the FID in FFD (using data for all species).…”

“…These studies may help the development of strategies to integrate human presence with the conservation of biodiversity, both in cities and in protected areas, supporting master and management plans, respectively. This subject has been well-discussed in temperate regions, mainly in Europe (e.g., CLUCAS & MARZLUFF 2012, MØLLER & IBÁNEZ-ÁLAMO 2012, MØLLER & LIANG 2012, DÍAZ et al 2013), but it is poorly known for the Neotropics (but see FERNÁNDEZ-JURICIC et al 2004, CARRETE & TELLA 2010. In Brazil, to our knowledge, there are no previous studies focusing on this issue.…”

“…Populations that have been present in urban areas for generations tend to have a lower escape distance compared to those in rural habitats as the members of urban populations become used to human presence, allowing a closer approach (COOKE 1980, MØLLER 2008, CARRETE & TELLA 2011. The urban individuals also face a lower risk of predation because predator densities in urban areas are generally lower (DÍAZ et al 2013).…”

The Degree of Urbanization of a Species Affects How Intensively It Is Studied: A Global Perspective

“…There is mounting evidence suggesting that this anthropogenic landscape change modifies different components of biodiversity, including taxonomic, functional and evolutionary diversity (Devictor et al, 2008;McKinney, 2008;Newbold et al, 2015;Ibáñez-Álamo et al, 2016;Knop, 2016;Morelli et al, 2016) and other aspects of the biology of organisms like animal behavior or life-history traits (Ibáñez-Álamo and Soler, 2010;Møller and Ibáñez-Álamo, 2012;Díaz et al, 2013;Gil and Brumm, 2014;Møller et al, 2015). This intensive alteration of the environment has attracted increasing attention by the scientific community (Marzluff, 2016;McDonnell and MacGregor-Fors, 2016) and has ultimately lead to recognize urbanization as a major global challenge (United Nations, 2016).…”

“…It is thus normal that many papers in the field of Urban Ecology have focused on investigating the interaction between organisms and humans. The majority of them focused on how humans can affect organisms, for example by altering animal's escape behavior (Díaz et al, 2013Samia et al, 2015), while others explored the opposite direction of the interaction, how urban nature can affect humans (Fuller and Irvine, 2010;Soga and Gaston, 2016). In relation to the latter, it is logical to think that scientists are not immune to this effect and the focus of their investigations might also be influenced by urban nature.…”