Looks like Twitter is steering away from it’s old icons and forcing us good web dev teams to make changes to all sites that use the old Twitter icon. They give us the bird with new guidelines that they outline here.
They DON’T Allow the birds referenced above :
Talking birds, dying birds, a family of birds, really blue birds, birds on the ground, cartoon birds or birds with hair, SO BE CAREFUL HOW YOU GIVE THE BIRD!
This is how they prefer to give us their pretty tweeting bird: