Mammals Species refers to the biological classification of diverse groups of animals that are warm-blooded vertebrates characterized by the possession of hair or fur, the secretion of milk by females for the nourishment of the young, and (typically) the bearing of live young. This category includes a wide range of animals such as bats, which are the only mammals capable of sustained flight, and herbivorous mammals, which primarily consume plant-based diets. It is a subset of the larger category of animals, specifically focusing on mammals.