Australia's birds never had a local predator like the cat. They just had to keep an eye on the sky for birds of prey and maybe snakes. It seems that efficient

Australia's birds never had a local predator like the cat. They just had to keep an eye on the sky for birds of prey and maybe snakes. It seems that efficient hunters are quite rare to evolve, as there have been lots of ecosystems totally turned on their head with the arrival of a new predator. Stoats, foxes, house cats have all found niches in ecosystems unfilled for hundreds of thousands of years and wiped out many local species. Or maybe the problem is that they are too good, and if left to themselves they would decimate their prey to the point they can't sustain their own numbers and die out; in the long term predators need to exist in an equilibrium.