Flush early and avoid the rush? It may depend on where you stand

Abstract

AbstractOptimal escape theory predicts that animals should flee at an optimal distance from the approaching predator (flight initiation distance, FID). However, FID usually increases with increasing alert distance (AD) or starting distance (SD). As an explanation for this pattern, the “flush early and avoid the rush” (FEAR) hypothesis states that prey should escape soon after detecting an approaching predator due to the cost of continuously monitoring risk. However, the positive relationship observed may also result from a mathematical artefact. Meanwhile, it is unknown whether animals would consistently follow this rule in different environmental contexts. We explored escape behaviours in light‐vented bulbuls (Pycnonotus sinensis) perched at different heights. FID generally increased with increasing AD and decreasing perch height. The positive relationships between AD and FID were outside the 95% confidence levels of simulated slopes from Monte Carlo simulations, suggesting that the relationships observed reflect biological effects rather than merely a mathematical artefact. Increasing perch height was also associated with longer buffer distance (defined as FID minus AD or SD), suggesting that the birds tend to delay their flush after detecting an approaching predator when perched high. The effects of environmental contexts (and the associated predation risk) on the AD‐FID relationship should be considered when performing inter‐specific comparisons or meta‐analyses.