Bird or butterfly?

Bird or butterfly?

Am I a bird or a butterfly,

Evading human eye

So swift and free?

Same size as a butterfly,

but moving rapidly

branch to branch,

My glowing mane and sharp beak

give me away,

Never still, I flit and flutter,

here and there I'll play.

I make soft, shrill cries,

my voice sharpening the air,

My black plumage glistens,

beyond compare.

Who am I?