BEAK
a bird's mouth is his beak
wren
word
Rail.
duck
HO-OH
Gull
ibis
A male bird is most commonly called a Cock.
BIRD! that has 4 letters doesn't it? :) Try Olor- It's a mute swan (whatever that means :/)
Rhea is a bird. It is 4 letters and starts with the letter R.
ROCS