Optimal running speeds when there is a trade-off between speed and the probability of mistakes

1. Do prey run as fast as they can to avoid capture? This is a common assumption in studies of animal performance, yet a recent mathematical model (Wheatley et al. 2015) of escape behaviour predicts that animals should instead use speeds below their maximum capabilities even when running from predators. Fast speeds may compromise motor control and accuracy of limb placement, particularly as the animal runs along narrow structures like beams or branches. Mistakes decrease speed and increase the probability of capture. 2. We tested several key assumptions and predictions of Wheatley et al.’s (2015) model using wild-caught northern quolls (Dasyurus hallucatus), a squirrel-sized marsupial carnivore. We quantified the speeds of quolls as they traversed beams of differing width and expected animals should balance the benefits of higher speeds against the increased probability of mistakes when selecting speeds. 3. We first explored whether the probability of mistakes when running along a beam ...