Flight-Initiation Distance in Birds Is Dependent on Intruder Starting Distance

The distance at which animals move away from approaching threats (often quantified as flight-initiation distance [FID], or flush distance) has been used by behavioral ecologists to understand the economics of antipredator behavior. Wildlife managers often use FID when seeking to develop set-back distances to reduce human impacts on wildlife. Economic models of escape behavior predict that escape decisions will be dynamic and will be influenced by both the costs and benefits of remaining. In contrast, wildlife managers often aim to generate a single set-back distance for each species. While a number of factors are acknowledged to influence FID, the starting distance between the observer and the animal is typically ignored in FID studies. For 64 of 68 species of Australian birds, I found a significant positive relationship between starting distance and FID. This demonstrates that, as predicted by economic models, species generally assess risk dynamically and flush at a greater distance as starting distances increase. My finding is consistent with the idea that animals accrue an attentional cost for continued monitoring of an approaching predator. Researchers or managers aiming to quantify human impact using FID should use starting distance as a covariate.