Rhythmic environmental changes caused by planetary movements are responsible for the evolution of life on Earth. Environmental and climatic variations prepare the animals to adapt themselves to the changing conditions accordingly. These changes in the environment ensure the most essential events occur optimally just once in a year, e.g. seasonal reproduction, hibernation, fur-colour change, etc., or at a particular time of day, e.g. sleep-wake, activity-rest cycle, etc. Seasonality in reproduction is an essential component of the life cycle for the perpetuation of species and is also the primary physiological phenomenon that is frequently and repeatedly being studied. It is among the major components of the “complex web” of seasonal physiological adjustments that permit organisms to protect their progeny and maintain a positive energy balance throughout the fluctuating ambient seasonal temperature and food availability in challenging environmental settings.