Whistling Tree Frog, or Brown Tree Frog (Litoria ewingii).
They are one of three Australian frogs to have naturalised in New Zealand (along with Litoria aurea and Litoria raniformus). Widespread and common in Australia and New Zealand, although may be declining due to Chytrid fungus.
This species was originally introduced in Greymouth and Manawatu, and has since spread as far north as Dargaville. In New Zealand it is capable of breeding continuously through winter. They are often heard singing during heavy frosts, and adults can even survive freezing (not recommended to try at home).