C - Cylinder
IC - Improved Cylinder
S - Skeet
M - Modified
IM - Improved Modified
F - FUll
XF - Extra Full
XXF - Extra, Extra Full (seen this once, but it may as well have been a turkey choke)
Then you get up in to your turkey chokes and whatnot.
For birds, I use anything from Cylinder to Skeet, but not really any tighter. I do, however, with my Over/Under shotgun, use IC on the top (first shot) and Modified on the bottom (second shot, with the bird usually being 20 yards farther away by the time I draw a bead on him again if I miss the first time.
I also have a Stoeger Model 2000. It is a great gun and does come with a lot of choking options out of the box--a nice feature to see in a sub-$500 auto. I use mine for duck hunting and crow hunting, since, in those two sports, I use considerably beefier rounds. For upland birds, I use my O/U, Beretta AL-2 and my Stoeger Uplander SxS .410.