What ARE birds?

Birds:

Show Content

SpoilerBird list:
Centipedes, Alligators, Bald Eagles, Penguins, Chicken, Spiders, Crows, Peacocks, Owls, Tyrannosauruses, Blue whales, Squid, kangaroo, gorillas, turtles, octopuses, roses, sunflowers, trilobites, crabs, lions, tigers, wolves, giant pandas, grizzly bears,


Some ____ are birds:
Birds, Passerines, domesticated animals, flightless birds, reptiles, primates, marsupials, strict-herbivores, insects, Non-animal organisms, monkeys, flowers, angiosperms, beetles, wasps, extinct organisms, felines, fish, canines, bears, sharks,


Not birds:
Humans, Snakes, Bees, Rotifers, Cockroaches, Worms, Mice, Annelids, Shrimp, Crocodiles, Gharials, Caimans, Ants, Canaries, Cassowaries, Housecats, Emus, Kiwis, Vultures, Herons, Ducks, Sparrows, Doves, Tabby cats, Dodos, Seagulls, Sperm Whales, Platypuses, all dinosaurs except Tyrannosaurs, ratites, kakapos, dogs, Elephants, unicellular organisms, all marsupials except kangaroos, venus fly traps, sea turtles, all fungi except mushrooms, gymnosperms, pacmen, termites, toads, hermit crabs, slugs, swans, coyotes, eels, unicorns, polar bears, brown bears, black bears, sloth bears, Anomalocarises

"Zoofights" while an extremely good guess are not birds.
Organisms who have never been represented in drawings are not birds.
Ghosts are not organisms so they are not birds
Some non human animals with sapience, maybe are birds
The organisms that share a taxonomical trait that is exclusive to organisms that are birds but is not simply a listing of the names of organisms that are birds are not birds.
Birds are not things that would make awesome names for sports teams.

Are mammoths birds?
Are pokemon birds?
Are extinct reptiles that are not dinosaurs birds?
Are yellow jackets birds?
Are hornets birds?
Domesticated animals besides chickens birds?

I don't think I'm figuring out what birds are so much as making an exhaustive list of all birds. There must be a reference or something I am missing?