Branching out in locomotion: The mechanics of perch use in birds and primates

Many animals use thin perches, such as the branches of trees, as locomotory substrates. In this paper, I have reviewed the literature concerned with m easurements of locomotory forces made by birds and primates on thin and fle xible substrates. Through a knowledge of the locomotory forces exerted by a nimals when using different substrates, the mechanical cost of their use ca n be established. We are just beginning to learn about the magnitude and pa tterns of force production in various branch-using vertebrates, primarily a s a result of the development of instrumented perches. Instrumented perches have been designed to measure the forces produced by birds and primates wh en leaping from rigid and flexible horizontal and flexible vertical perches , and also from instrumented handgrips during brachiation, The development of these techniques for birds and primates allows us to compare the way in which they use perches as locomotory substrates. In both birds and primates, the magnitudes of landing forces are smaller th an those during take-off. Two explanations have been proposed; the differen ce is either a consequence of perch compliance or it is a strategic decisio n to be cautious of 'new' perches. Leaps from flexible perches may be somew hat inefficient because considerable energy is dissipated in bending the pe rch, and this energy may remain unrecovered when the animal leaves contact with the perch.