With such methods as these, a great variety of animals nourish themselves on the vegetable foods provided by the forests of the world. Up in the topmost branches, rodents such as the grey squirrel (Sciurus carolinensis) scamper along the twigs, collecting bark and shoots, acorns and catkins. Some species have even developed furry membranes between their hind and fore legs so that they can glide between the branches and thereby improve their foraging efficiency. These are called flying squirrels, and there are over forty species of them, and they are concentrated almost in the Asiatic region (e.g. the Red and White Flying SquirrelPetaurista alborufus) with seven species occurring in Africa (e.g. Pel's Flying Squirrel Anomalurus peli) two species occurring in North America (e.g. Southern Flying SquirrelGlaucomys volans).