It depends on the species on what croak, how long, and how loud a croak is. However, each mature frog in the spring has one thing on its mind: to mate. So they hop into a pond and start singing away, only stopping when interrupted (in which they start again a minute later) when they find a mate (they will start croaking again once they are done) or when it is no longer dark. Some frogs are known to croak in large groups, infact. the PTF (Pacific Tree Frog- also known as the Pacific Chorus Frog) find a pond a pond, and start singing. Both the females and males hear this. The females come to mate- the males come to join the group singing, hopping they too will get a mate.