The Fixed Slope Rule: An Inter-Specific Study

Abstract

There are two broad mechanisms by which animals can assess risk when deciding whether to flee: temporally and spatially. Animals that employ temporal mechanisms use predator speed to gauge threat. In contrast, those that use spatial mechanisms use the distance to the predator as an indication of danger. Traditionally, this was viewed as a fixed distance. Recently, a new type of spatial mechanism was proposed that focused on animals initiating flight at a fixed ratio of the distance at which they first responded to the threat. Our study investigated the consistency of this slope among three species: the Eastern gray kangaroo (Macropus giganteus), the Australian wood duck (Chenonetta jubata), and the Australian magpie (Gymnorhina tibicen). We found that these species exhibited statistically indistinguishable slopes from each other and the 0.44 slope that was initially reported in another species. Our results further support the assumption that escape decisions are dynamic. Future studies should determine the ubiquity of this fixed ratio.