Developing an evolutionary ecology of fear: how life history and natural history traits affect disturbance tolerance in birds

When approached by humans, virtually all species flee, but we lack an understanding of the factors that influence flight response among species. Understanding this variation may allow us to understand how ‘fear’ structures communities, as well as to predict which species are likely to coexist with humans. I used flight initiation distance (FID) as a comparative metric of wariness and examined the relative importance of life history and natural history traits in explaining variation in FID in 150 species of birds. In a series of comparative analyses, I used independent contrasts to control for phylogenetic similarity and regressed continuous life history traits against flight initiation distance. Body size had a large and significant effect in explaining variation in flightiness: larger species initiated flight at greater distances than smaller species. After controlling for variation explained by body size, there was a nonsignificant positive relation between the age of first reproduction and FID. There were no relations between FID and clutch size, number of days spent feeding young, longevity, or habitat density. I used concentrated changes tests to look for evidence of coevolution between flightiness and dichotomous traits. Flightiness evolved multiple times and some clades were flightier than others. Flightiness was more likely to evolve in omnivorous/carnivorous species and in cooperatively breeding species. These results suggest that body size and age of first reproduction are important in explaining variation in disturbance tolerance in birds, and that species that capture live prey and those that are highly social are relatively wary. The results suggest a novel mechanism of how anthropogenic disturbance may contribute to extinction.