The Landing Forces of Domestic Pigeons

Abstract

THE force with which a bird lands on a perch may have considerable ecological and anatomical significance. This force, along with the body weight of the bird, may determine the type of perch used for roosting at night and the sequence of perches or landing areas used in approaching the nest, and it may even play an important role in habitat selection. For example, it is difficult to envision a Mallard or a Pintail Duck landing on even the larger branches of a tree, if one has ever observed the apparent force with which these ducks hit the water. Other ducks of similar body weight do land in trees. Large herons may be seen landing very lightly on the smaller twigs of trees and bushes and on soft mud; much lighter birds of similar pedal structure almost never utilize such landing places. Such differences in landing may result from differences in habit, in structure, in behavior, or in the situation encountered. The force with which a bird lands is not solely a function of its weight; action of wings, of tail, and of legs modify this force, as does the pattern of landing. For the student of functional anatomy, the landing force may be a means of studying the locomotor organs-wings, tail, and legs. In the literature we find no information relative to the forces with which any of these appendages move. Wind tunnel experiments to determine flight characteristics of airplanes are fairly successful because, compared to the avian wing, the wing of an airplane is very simple. It has been estimated that there are at least ten times as many variables in the wing of a bird. We cannot yet measure the force of the movement of the wing or the tail when these parts are in use, under natural or experimental conditions, although it is not difficult to imagine a large bird trained to fly with small transistors attached to various parts of its body to record a host of data. Fisher (in press) has described an apparatus that makes possible the actual measurement of leg thrust when a bird takes off or lands. Knowing the force of the legs at the time of the take-off and the weight and speed of the bird, it is possible to calculate the force that must have been supplied by the wings during take-off. At the time of landing there are three major groups of variables-the parts of the wing, of the tail, and of the leg. If the force of landing of a bird is constant under certain controlled conditions, any change in one of these groups may be reflected in different forces being exerted by one or both of the other groups. Unfortunately, because the force