Comparing perceived risk of predation in urban birds

Abstract

To thrive in urban environments, birds need to make behavioral adjustments to tolerate the disturbances and threats that are imposed by these environments. Birds constantly need to adjust their assessment of predation risk to maximize their fitness in these environments. Such adjustments can be measured through different reaction distances to an approaching predator, such as flight initiation distance (FID) and distance fled (DF). Using these variables, we compared the perceived risk of predation of 12 bird species in formal (i.e., public parks; FGS) and informal greenspaces (i.e., vacant lots; IGS) in a Latin American city. We also compared these behavioral responses between native and exotic species and explored whether different factors, such as predator abundance, disturbance level (e.g., noise, pedestrians), and other reaction distances (e.g., buffer distance), could help us explain an eventual difference of perceived risk of predation in both habitats. We measured 199 distances in individual birds, of which 104 were obtained in FGS and 95 in IGS. Birds in FGS had significantly shorter FID and DF than birds in IGS, but data variability was higher in IGS than in FGS. This suggests that birds perceive FGS as safer habitats than IGS, and/or that birds in FGS are more tolerant to the presence of humans. Exotic birds were bolder (i.e., shorter FID) than native birds, but native birds had more variable FID and DF than exotic birds, suggesting that native birds could eventually become as successful as exotic birds in colonizing urban environments. The FID was better explained by other reaction distances (i.e., starting and buffer distances) than by the abundance of predators or intensity of disturbance. These findings agree with the “flush early and avoid the rush” hypothesis and with the high availability of resources in both habitats. Our results suggest that IGS can provide refuge to fearful birds and at the same time be a source of bolder behavioral phenotypes allowing bird populations to scale their tolerance to urbanization.