What ARE birds?

Not all beetles are birds.
Am I a bird? .....I refuse to testify.
Lamps are not birds.
Vacuum cleaners are birds.
Bacteria are not birds.
Viruses are not birds.

Rocks are not birds.

Not all mammals are birds.
Not all fish are birds.
As answered before, not all reptiles are birds.
Amphibians might all be birds.
Not all invertebrates are birds.

Clocks are birds.