Bird flight

Abstract

Avian flight has fascinated man from ancient times but it is only in recent years that the efforts of scientists from diverse fields have been able, to some extent, to understand and explain the dynamics of animal flight. This article is based on some observations of birds in the Nellapetu and Pulicat Lake sanctuaries on the east coast of India. It essentially summarises the results of application of well-known principles of elementary incompressible aerodynamics to the flapping and gliding flight of birds. For a reader unfamiliar with the subject, brief notes on evolution of animal flight, the occurrence and classification of bird species and a description of the structure and musculature of wings and feathers and elementary theories of lift and drag are included. Observations show an incredible diversity of flight techniques and manoeuvers. A general description of the main types of bird flight and some illustrations of wing shapes and the motion of birds while taking off, landing and hovering are given. Viewing the flapping wing as a quasi-steady device imparting momentum to the air surrounding it through the expenditure of muscular energy derived from oxidation of fat, estimates of the power required to fly and that available from metabolic energy conversion can be made. Gliding and soaring flight can then be understood reasonably well. Approximate results of bird performance including range and endurance can also be obtained for steady flapping flight. However it is still not possible to calculate and predict in detail all aspects of the flight of a specific type of bird. Only a brief mention is made of the essentially nonlinear and non-steady nature of the aerodynamics of flapping bird wings which needs further research. Using dimensional analysis, the effects of bird size and weight are discussed. The intriguing question of relating the processes of natural selection for a given species in evolving a particular wing shape and flight mode that must be conducive to its continued survival remains open for much further research and study.