Apparatus to Measure Forces Involved in the Landing and Taking Off of Birds

Abstract

Study of the ways in which animals are adapted to live successfully in a particular situation has long been of interest to biologists. The early naturalists observed and theorized about some of the more obvious adaptations-the long legs in wading birds and the power of flight, for example. Explanation of the functioning of most of these gross adaptive mechanisms has been unsatisfactory. Consider the wing of a bird. We can observe the movements it makes. By study of the structural components-the bones and muscles in a carcass -we note that shortening of a muscle or of a group of muscles may cause this or that movement. In a living bird, held stationary, electrodes inserted in various muscles may provide a means of correlating a movement and the contraction of a muscle or muscles. But these observations must be interpreted subjectively, and they are made under artificial and perhaps misleading conditions. Investigation of such natural phenomena as the action of a muscle in a particular movement of the bird wing must be conducted in living, freelyflying birds. Further, there must be some quantitative measure of differences in function, if the results of these researches are to have inherent validity, to possess value for comparison with the findings of other workers, and to be of use in determining the degree of adaptation of a structure. For several years I have tried to study the role of certain muscles in the wings of pigeons. Muscles have been removed, individually and in groups. Tendons have been cut, and muscles enervated. Slow-motion moving pictures taken before and after surgery were used to demonstrate loss of function. It was difficult to assess the amount of change. The arc of the wing was "shorter," the tip of the wing was "not pulled quite so far forward," the alula "seemed to be used to a greater extent," and other similar subjective and indecisive observations were made. However, all the birds (68 individuals, involving 12 different surgical techniques) flew well in the large outdoor cages, maintained their body weights and, in general, were indistinguishable from control birds in the same cages. It was evident that a precise, quantitative method of ascertaining the change or loss of function had to be perfected.