Sudeep, you need to be more precise with your question. Fourier analysis deals with functions, the flapping of a wing is not a function. However, there are many functions you can define on the basis of wing flapping - for example, the position of the wing tip as a function of time, the wing angle of incidence, the energy dissipated as the wing flaps, the forces on the wing, etc. Any such quantity expressed as a function of time or distance in periodic cycles is something you can analyze with Fourier series.