Effect of visibility on time allocation and escape decisions in crimson rosellas

Abstract

Most studies of antipredator behaviour have focused on a single behaviour at a time, but ubiquitous factors may simultaneously influence a variety of activities. Habitat structure influences visibility, which influences both the ability of prey to detect and respond to their predators. We studied how habitat visibility influenced time allocation and escape decisions of crimson rosellas (Playcercus elegans). We examined the effect of visibility on time allocated to looking, locomotion and foraging. We measured escape decisions by experimentally approaching rosellas until they fled. We measured visibility by standing 12 m away from a 1-m2 white sheet containing 36 points and counting the number of points that were visible. As measured, visibility influenced time allocated to both foraging and locomotion. However, there was no effect of visibility on flight-initiation distance or two other related measures of escape (a measure of the latency to detect an approaching threat or the latency to flee once the threat was detected). Therefore, crimson rosellas modified their behaviour as a function of visibility, but this did not influence their decision to flee from an approaching human. We infer that they are sensitive to variation in visibility, but that this does not influence their overall perception of risk as we measured it. These two stages of antipredator behaviour may thus be largely independent; ubiquitous factors need not have ubiquitous effects on different aspects of antipredator behaviour.