Just wanted to chime in a little more on New Zealand. Black Sheep already touched on it, but this is a really fascinating case study for evolution. Since there was no mammal competition, birds have evolved to take over every ecological niche normally filled by mammals. There are even birds that fill a role akin to moles.
Also, the idea that animals just kind of migrated to where the climate was right for them after Noah's Flood is blown away by observing that when foreign animals are introduced to places such as New Zealand by humans, they thrive. It's not a matter of the poor mammals just not being able to survive in New Zealand, it's that they never got there.
SNG