Like, I’m aware of there being exceptions like Penguins, Ostriches, and Bats. But in general, why is there such a distinct land/air split between mammals and birds? Why don’t mammals share the ground with ecosystems of plant- and meat-eating walking birds? Why didn’t we get birds that evolved to slither like snakes, or tunnel like rodents? Why isn’t it (land+sky) all just mammals, where we’d have parrot- and vulture-like bats that don’t lay eggs? If we started the simulation again, might things like this evolve?
Flight requires extreme adaptations that make terrestrial life much more difficult. It’s hard to evolve it and once you do, going back will be difficult. Especially when competing with a bunch of animals that haven’t completely warped their bodies for a totally different lifestyle.
On isolated islands without mammals, many birds do begin to revert to a terrestrial strategy. But the mammal body plan is just better for this, and when mammals have reached such places, flightless birds have almost immediately experienced population collapse.
New Zealand bird life in a nut shell
Yeah we have plenty of flightless birds here (or rather HAD), birds burrow and ground nest, bats that spend a lot of time ground foraging, insects that grow to the size of small rodents, carnivorous snails (https://www.youtube.com/watch?v=ubNm5M2-LAc) and more
https://www.youtube.com/watch?v=Y0fbYuvSIY0&t=227
Woah. I never thought I’d see a bird run this fast