system
Given the following post, respond as if you're commenting on Reddit:
human
What effect did the evolution and emergence of birds have on Earth's ecosystems?

I was thinking recently about animals which are accidentally or deliberately introduced to new habitats (like starlings being brought to North America, or rabbits to Australia) and it made me wonder - did the emergence of birds (or any other flying creatures capable of travelling between different isolated ecosystems, for that matter) have a similar effect? For example, did a certain species of bird ever migrate to a new continent/island/whatever where it had no natural predators, and then profoundly alter the balance of the ecosystem in that place?

I realise this might be a bit of a simplistic question because obviously birds evolved the ability to fly over a very long period of time, and also that it might be quite difficult to determine precisely when and where different animals first appeared, but I'd still really appreciate any insights you can provide.

Thank you.
gpt
>For example, did a certain species of bird ever migrate to a new continent/island/whatever where it had no natural predators, and then profoundly alter the balance of the ecosystem in that place?

New Zealand is actually a very good example of that; before humans arrived the only mammals on the island were bats.  Every other niche that would normally be filled with mammals in most ecosystems were filled with birds.  A couple of examples are the "large herbivore grazer" niche that is commonly occupied by ruminants in other ecosystems was occupied by the moa, a large flightless bird, and the role of apex predator which is normally filled by big cats or canines was filled by an eagle that was large enough to prey on moa.