Four Letter Birds

Duck
Tern
Loon
Gull
I'iwi*
Crow
Wren
Coot
Teal
Kiwi*
Lark
Nene
Swan
Smew**
Ibis
Kite
Hawk
Dove
Myna

^* In Hawaiian it's "`i`iwi", and the `okina is a letter, so it's a six-letter bird, but its English name counts as 4 letters.
^** not sure if I've ever seen one in the wild.

Added from the comments: Rook, Dodo, Kaka, Weka, Cock

Bonus list: Four letter birds I found on Wikipedia that I'm not sure I was aware of before:
Kagu
Sora
Rail
Ruff
Skua
Koel
Coua
Iora
Guan

Point of ambiguity: Does "Bird" belong on the list?