Raptors and fear of humans: variation on the degree of aversion in relation to urbanization

Fear of humans is a behavioral feature that could determine the presence and establishment of certain species in an urbanized environment. This behavioral feature has been quantified in birds as Flight Initiation Distance (FID). We tested whether urbanization has an effect on the degree of fear of human presence in La Pampa’s raptors population. We obtained a total of 95 FIDs from 13 towns with different population sizes (573-57,669 inhabitants). The sampled environments were rural (N=23), suburban (N=55) and urban (N=17). Only Athene cunicularia (N=35), Caracara plancus (N=8), Falco sparverius (N=5) and Milvago chimango (N=47) were taken into account for data processing. The FID was 22.26 ± 23.12 m (Min = 2.5, Max = 168.29). Generalized Linear Models were constructed; which have detected the environment as the most significant variable that accounts for the FID variation, whereas the distance between a waypoint where the FID was measured and the town centre, and the inhabitants were not significant. Results show that the lower FID belonged to birds of the urban environment (11.96 ± 7.74), a higher one for the suburban (22.10 ± 20.60) and the highest FID in rural (30.25 ± 32.41). This decrease in the fear of humans, which applies to raptors living in highly anthropized environments, shows that urban development may constitute a selective force that prevents the entry of the birds with greater aversion to humans.