What ARE birds?

are mitocondria birds
are chloroplasts birds
are hovercraft birds
are bipedal robots birds

are birds things that move on limbs?

minotaurs could be birds
mitchondria are not birds
chloroplasts are not birds
hovercrafts are not birds
bipedal robots might look like birds but are not birds
birds are not things that move on limbs

is an upright piano on two stilts a bird
is the eiffel tower a bird
is the eiffel tower, if it were bisected through its length, a bird

is the arch in st louis a bird

are amoebae birds
are gram-positive bacteria birds
are gram-negative bacteria birds
are fungi birds

are vines birds
are AT-ATs birds

are sharks birds?

are extra dimensional demons birds?

is snoop dogg a bird?

are turtles birds?

is an upright piano on two stilts a bird

no

is the eiffel tower a bird

no

is the eiffel tower, if it were bisected through its length, a bird

see above

is the arch in st louis a bird

no

are amoebae birds

no

are gram-positive bacteria birds

some might be but likely no

are gram-negative bacteria birds

some might be but likely no

are fungi birds

no

are vines birds

no

are AT-ATs birds

no

are sharks birds?

yes

are extra dimensional demons birds?

possibly

is snoop dogg a bird?

humans are birds

are turtles birds?

some turtles might seem not birds, but overall, turtles are birds

This has me stumped...

Are dolphins birds?
Are american finches birds?
Is an effigy of an eagle a bird?
Is a mechanical eagle a bird?

Dolphins are birds
American finches are birds
eagle effigies and mechanical eagles are not birds

Is a non-breathing eagle a bird
Are oxidizing bacteria birds

A bird is a cellular organism that metabolizes oxygen (?)

Are mollusks birds?
Are bivalves birds?
Are ducks birds?
Are pigeons birds?
Are owls birds?
Are vultures birds?

eagles are birds
some oxidising bacteria might be birds but most probably aren't
not all cellular organisms that metabolise oxygen are birds

not all molluscs are birds (snails are not birds, slugs are not birds)
most bivalves are not birds but a few are birds
ducks are birds
pigeons are birds
owls may seem like birds but a few are in fact not birds
vultures are birds

Are mysticetes birds?
Are barn owls birds?
Are jellyfish birds?

mysticetes are birds
you have to look carefully to notice but barn owls are not birds
jellyfish are birds

Are monodontidae birds?
Are physeteridae birds?
Are kogiidae birds?
Are ziphiidae birds?

Are porpoises birds?

Are all animals under the genus tyto birds?
Are Tytonidae birds?
Are true owls (strigidae) birds?

mysticetes are birds

After review, mysticetes are not birds, sorry for any unintended confusion

Most if not all monodontidae, ziphiidae and porpoises are not birds
It is difficult to say if the physeteridae &/or kogiidae are/were all birds or not but Physeter macrocephalus is definitely not a bird
Tytonidae (and by extension, Tyto) are not birds
Some strigidae are birds

Are Delphinapterus birds?
Are beluga whales birds?

Were Denebola birds?
Were Bohaskaia birds?

Are Monodon monoceros birds?
Are narwhals birds?

Were Haborophocoena birds?
Is the finless porpoise a bird?
Is the narrow-ridged finless porpoise a bird?
Were Numataphocoena birds?

Is the harbor porpoise a bird?
Is the vaquita a bird?
Is the spectacled porpoise a bird?
Is Burmeister's porpoise a bird?
Is Dall's porpoise a bird?

Were S. bosselaersii birds?
Were Piscolithax birds?

Is the dumpster behind the outback steakhouse a bird?

Ok, I'm going to just jump over most of that and just state that othodoncetes are not birds - but it is difficult to say when they stopped being birds precisely
Also I just found a study that suggests mysticetes are in fact birds all along and my original instincts were right

mysticetes birds, othodoncetes not birds yes good let's move on

Is the dumpster behind the outback steakhouse a bird?

there may be birds and not birds inside the dumpster behind that infernal place but the dumpster itself is not a bird

if it helps, out of those listed, the narwhals are the easiest to define as not birds

Are walruses whales?
Are snails birds?
Are warthogs birds?

walruses are birds
snails are not birds (already asked)
warthogs are birds

are polar bears birds?

Polar bears are birds

Birds have exposed mineralization only on / inside their eating apparatus.

Birds do not have exposed mineralization only on / inside their eating apparatus

Is it ok for a hint? Is birdness based on a physical attribute?