The eggs may be retained until hatching and get all of their nutrients from the yolk and the young are born as larvae. In one species the embryos get nutrients from oviductal secretion and are born much larger and more fully developed. Some species, especially arboreal frogs, have longer limbs and move by walking and climbing using all four feet. Because of the mechanism by which the toes can cling or not to a surface, a frog must orient with its head facing up for its toes to cling to a surface. Calls Frogs and toads are very vocal and much research has gone into studying these calls.
Calls are species specific and serve as pre-mating isolating mechanism for many species.
In most species, only the males call. Calling has a cost. In most anurans, fertilization is external. Males and females engage in amplexus , in which the male is on the back of the female and he grasps the female with his forelegs. Amplexus is usually maintained for several hours but may be maintained for several days.