The Behavioral Ecology of Intermittent Locomotion

Most physiological and ecological approaches to animal locomotionare based on steady state assumptions, yet movements of manyanimals are interspersed with pauses lasting from millisecondsto minutes. Thus, pauses, along with changes in the durationand speed of moves, form part of a dynamic system of intermittentlocomotion by which animals adjust their locomotor behaviorto changing circumstances. Intermittent locomotion occurs ina wide array of organisms from protozoans to mammals. It isfound in aerial, aquatic and terrestrial locomotion and in manybehavioral contexts including search and pursuit of prey, matesearch, escape from predators, habitat assessment and generaltravel. In our survey, animals exhibiting intermittent locomotionpaused on average nearly 50% of their locomotion time (range6–94%). Although intermittent locomotion is usually expectedto increase energetic costs as a result of additional expenditurefor acceleration and deceleration, a variety of energetic benefitscan arise when forward movement continues during pauses. Endurancealso can be improved by partial recovery from fatigue duringpauses. Perceptual benefits can arise because pauses increasethe capacity of the sensory systems to detect relevant stimuli.Several processes, including velocity blur, relative motiondetection, foveation, attention and interference between sensorysystems are probably involved. In animals that do not pause,alternative mechanisms for stabilizing the perceptual fieldare often present. Because movement is an important cue forstimulus detection, pauses can also reduce unwanted detectionby an organism's predators or prey. Several models have attemptedto integrate energetic and perceptual processes, but many challengesremain. Future advances will require improved quantificationof the effects of speed on perception.