What ARE birds?

I don't think taxonomy is a big deal for birds right now.

All of the mentioned birds are relatively popular animals. The T-rex is the only dinosaur that is a bird, Alligators are birds but not crocodiles, I wouldn't be surprised if kangaroos are the only marsupial birds and gorillas are the only primate birds.

Saying that animals that have not been represented in a drawing are not birds suggests that the category of what constitutes a bird is a reasonably referencable list, and that it is not a particular physical or behavioral trait of the organism.

Also zoofights, for anyone wondering, was a repeating collaborative web-comic/popularity contest wherein mutilated versions of animals fought one another and ridiculousness happened. Akumu actually did some of the art for one!

What I'm not sure of though is where birds come from.


Are marsupials that are not kangaroos birds?
Are primates that are not gorillas birds?
Are venus fly traps birds?
Are sea turtles birds?
Are non-human animals with sapience birds?
Are passerines that are not in the order Cordova birds?