Tons of avian backgrounds and art - just be sure to give them credit.
Clipart for dark backgrounds.
Here are some really fun graphics!
Check out the Birdset.
Images by Evan
If your site is family-oriented, they've got graphics for you.
Inca's Graphic Grotto
Parrot buttons with matching backgrounds, and animation.
Parrot Publishing and Design
A compendium of graphics which covers many species.