Why is there a frog at Nathan's house, what is it?

Keen First Uppers will have been gripped last week by the story of the mystery frog that appeared in a water feature at Nathan Rarere's house ... We're calling him Herbert the Frog. Nathan doesn't live near a pond, or a lake so he wanted to get to the bottom of how he got there. To answer his many frog-based questions we got hold of Richard Gibson who is the Head of Life Sciences at Auckland Zoo. Nathan asked him to about our native frogs, which to be honest he didn't know much about.