If frogs return to breed where they hatched, how do they spread?

If frogs return to breed at the place where they hatched, how do they spread across the country?

Hugo Cayuela, University of Lyon, France

For a long time, naturalists thought that amphibians (such as frogs, toads, salamanders and newts) were philopatric animals. This means that, if a frog began life in a given pond, it will always come back to breed in this pond when it is old enough to do so.

However, this view suffers from obvious contradictions.

First, the populations of some species of amphibians occupy large geographical areas, which implies movement between ponds to colonise these vast…