Optimal locomotion modes of foraging birds in trees

Abstract

This paper compares the energy costs of various modes of locomotion of birds foraging in trees. For birds moving vertically in trees by climbing and hopping (but not by flying) the best choice of locomotion mode depends on the distance between visited trees in relation to the height h of the zone searched for food in trees.When the distance between successively visisted trees is longer than about half the distance coverable in gliding flight with height loss h, then it is cheapest in energy to hop or climb upwards in a tree and fly downwards to the next tree. When the distance between successively visited trees is shorter than about half the distance coverable in gliding flight with height loss h, then it is cheapest in energy to move alternately downwards and upwards in trees (downwards in the first, upwards in the second, downwards in the third tree, etc.) and to fly level between trees.Treecreepers and woodpeckers are adapted morphologically to the former mode, but more generalized tree foragers might use either mode depending on the spacing of trees.