What ARE birds?

I have a range of possible hints - Most of the ones I've given out so far I would rate a 1/5 in terms of how obviously they clarify what birds are.
Pick a rating, and I'll tailor my next hint to suit.

Taunting and educating at the same time?

Man, what separates hourglass dolphins from ALL OTHER oceanic dolphins, AND differentiates red pandas from giant pandas, and Toco tucans from keel billed toucans. It doesn't seem to be related to coloration - we don't know what color a dimetridon was and it is not a bird.

Yeah lets crank this up to 2/5.

Meanwhile among carnivorous plants:

Are pitcher plants birds?
Are venus fly traps birds?
Are sundew plants birds?

And
Are vulpes vulpes birds?

Are Anomalocaridids birds? (I think that's the proper plural)
Are octopodes birds?
Are stegosauri birds?

Not all pitcher plants are birds.
Venus fly traps are birds!
Not all sundew plants are birds.

Red foxes are birds!

No species of anomalocaridid have the requisite feature to qualify as birds.
Not all octopodes are birds.
Stegosauruses are not birds.

Hint rating 2/5: Bandicoots are birds!

(Nope, that was the family, not the plural. Ah well, the question is moot anyway, since none of them are birds.)

Are blue-ringed octopodes birds?
Are common octopodes (Octopus vulgaris) birds?

Birds are animals with a V in their scientific name?
nope, that's wrong.

Are pachyderms birds?

Neither blue-ringed nor common octopuses are birds!

Glass octopus, Antarctic knobbed octopus, boxer octopus, giant Antarctic octopus, and two species in the genus Octopus are birds!

Elephants, rhinos, and hippopotamuses are not birds.

Correction; elephants are birds. Apologies, and to make up for it, a hint:

Screaming hairy armadillos are birds, but maned sloths are not birds

Are species that have not been discovered birds?

Are you a birds, Schazer? Has there been something you're not telling us?

I think it's time we turn that dial up to 3/5.

Are birds creatures that remind us of our limited time on earth?

As-yet undiscovered species lack the required feature to qualify as birds.
Birds are not creatures that remind us of our limited time on earth.

Hint rating 3/5: Pink fairy armadillos are birds. Maned sloths are not birds.

OKAY.

So birds have to do with traits that only-discovered species have. So this is not about any physical characteristic or trait but a human or taxonomic imposed trait.

So lets look at some scientific names:

Some Birds:

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Spoiler

• Chlamyphorus truncatus
  
• Chaetophractus vellerosus
  
• Lagenorhynchus cruciger
  
• Vitreledonella richardi
  
• Dionaea muscipula
  
• Crocodylus niloticus
  
• Crocodylus porosus
  
• Bathypolypus valdiviae
  
• vulpes vulpes
  
• Ailuropoda melanoleuca
  
  

Some Not Birds:

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• Bradypus torquatus
  
• Octopus vulgaris
  
• Orcinus orca
  
• Tursiops truncatus
  
• Tursiops aduncus
  
• Canis familiaris
  
• Ailurus fulgens

Cursory glance doesn't reveal a pattern...

Are anteaters birds?
Are 2 toed sloths birds?
Are Dasypus novemcinctus birds?

Giant and Silky anteaters are birds, but tamandua are not birds.
two-toed sloths are not birds.
9-banded armadillos are not birds.

Are robins birds?
Are European Robins birds?
Are Japanese Robins birds?

Are tabby cats birds?

Are four-toed earless skinks birds?
Are four-toed hedgehogs birds?
Are four-toed elephant shrews birds?
Are four-toed jerboas birds?

Are any dinosaurs birds?

Are komodo dragons birds?
Are bearded dragons birds?

Going out on a poorly researched limb here, but are birds organisms which have had their taxonomic classifications changed?

Are any fictional animals birds?
Is the indominus rex a bird?

Neither the European, American oro Japanese robins are birds. Not all members of the genus Petroica are birds.

Cats are not birds.
Four toed earless skinks are not birds.
Four toed elephant shrew and jerboas are birds!
Four toed hedgehogs are kind of birds? I'd feel bad calling it one way or another.

Not all dinosaurs are birds.
Komodo dragons are not birds.
Bearded dragons are birds!

Birds are not organisms which have had their taxonomic classifications changed.
I cannot ascertain if all fictional animals are birds or not, please provide examples.
Indominus rex does not appear to be a bird.

A hint: birdness is not predicated on scientific names. All species have a scientific name.
Boxfishes are birds!
Pyramid butterflyfish are birds.
Orbfishes, alternately called Round spadefishes, are not birds.

Are manta rays birds?

manta rays are birds!

Are birds creatures whose common names coincide with their physical traits?

Are Ewoks birds?
Are Tribbles birds?
Are Sarlaccs birds?
Are Gungans birds?
Are Yoshis birds?
Are Metroids birds?
Are Zombies birds?

birds are not creatures whose common names coincide with their physical traits.

None of those things you just mentioned are birds.

Maned sloths are not birds.

Are birds the lesser extant species of their given subfamily?

birds are not the lesser extant species of their given subfamily!

MASTERPOST

I've removed things from the 'not all' category when there's examples of the larger group in both the Yes and No answers. (Reasonably) larger groups in straight Yes or No are bolded.

Yes: Antarctic Knobbled Octopuses, Arctic Foxes, Bandicoots, Bearded Dragons, Boxer Octopuses, Boxfish, Bullet Ants, Caimans, Chickens, Common Whelks, Elephants, Fennec Foxes, Giant Antarctic Octopuses, Giant Anteaters, Giant Pandas, Glass Octopuses, Golden Orb Weaver Spiders, Hourglass Dolphins, Howler Monkeys, Keelbilled Toucans, Naked Mole Rats, Pink Fairy Armadillos, Pyramid Butterflyfish, Rattlesnakes, Red Foxes, Screaming Hairy Armadillos, Silky Anteaters, Tree Wasps, True crocodiles, Venus Fly Traps

Kind Of: Four toed Hedgehogs

Probably Not: Indominus rex

Not All: Angiosperms, Bears, Carnivorous Plants, Dinosaurs, Gymnosperms, Mosquitos, Mosses, Pitcher Plants, Pufferfish, RiverDolphins, Robins, Sessile Animals, Spiders, Sundew Plants

No: 9-Banded Armadillos, Alligators, American Robins, Anacondas, Anomalocaridids, Blue-ringed Octopuses, Cats, Common Octopuses, Dimetrodons, Dogs, European Robins, Ewoks, False Gharials, Four toed Earless Skinks, Four toed Elephant Shrews, Gharials, Gungans, Hippopotami, Honeybees, Humans, Japanese Robins, Jerboas, Komodo Dragons, Maned Sloths, Manta Rays, Metroids, Oceanic Dolphins (Except Hourglass), Orbfish, Platypuses, Ptarmigans, Red Pandas, Rhinoceri, Sarlaccs, Stegosauruses, Tamandua, Toco Toucans, Tribbles, Two-toed Sloths, Yoshis

• Birdness is determined taxonomically, so "birds are species which _______" is a good way to think about it, yes.
  
• A hint: birdness is not predicated on scientific names. All species have a scientific name.
  
• Not all unicellular organisms are birds, nor are all prokaryotes. Probably. There's a chance that either of the above are not birds, and establishing as such is really goddamn time-consuming.
  
• I cannot without extensive research confirm whether or not all ferns are not birds.
  
• No species of anomalocaridid have the requisite feature to qualify as birds.
  
• As-yet undiscovered species lack the required feature to qualify as birds.
  
• Four toed hedgehogs are kind of birds? I'd feel bad calling it one way or another.
  

• Birds are not animals with sharp teeth or pincers.
  
• Birds are not the lesser extant species of their given subfamily.
  
• Birds are not organisms which have had their taxonomic classifications changed.
  
• Birds are not creatures that remind us of our limited time on earth.
  
• Birds are not species which hide for some time then reappear later.
  

QUESTIONS

You said 'Orcas are not whales.' - are Orcas birds?
Are Felines birds?