Frogs sing to attract females for mating. In almost all frogs, egg fertilization happens outside the female's body instead of inside. The female releases her eggs and the male releases his sperm at the same time. In order to make sure that the sperm reach the eggs, the male and female get into a mating posture called amplexus.
The male climbs onto the female back and clasps his forelegs around her middle. Frogs can stay in amplexus for hours or even days as the female releases as few as one or as many as several hundred eggs in a single round.