Migration is nearly universal within the animal kingdom; Animals across the globe, from birds and mammals to reptiles and insects, migrate for a whole variety of different reasons. Resources on Earth fluctuate and change constantly. Warm summer months may be followed by inhospitable cold. Plants may be in abundance in one place, but only for a short time. The best place to find food may not be a good place to give birth or hatch young. All these changing factors lead to animals needing to move to a better suited environment at different times of the year. The motivations behind migrations are simple. Food, breeding and climate.