New Zealand is an island that is fairly far from other land masses, so all the life that ended there, would have to find a way to reach it. Humans can build boats, but what about other species?
Birds can fly, and while they fly, they can bring seeds, for example in their stomachs.
So the birds that could fly to New Zealand found a safe enviroment there and thrived without many predators!
the answer is: Plants and birds would make ocean crossings to the isolated New Zealand island, mammals could not.
