What ARE birds?

Okay let's do this thing.

Some plants are birds.
Some fungi are birds.
Bacteria are not birds.
Archaea are not birds.
Protists are not birds.

Gatr's question is not well-posed! At this stage I don't think I will answer.

Non-kangaroo marsupials are not birds.
Some non-gorilla primates are birds.
Venus fly traps are not birds.
Sea turtles are not birds.
Some non-human animals with sapience are birds, maybe.
All passerines are in the order Passeriformes, so, some.

Ghosts are not organisms so are not birds.