Do you practice with the same loads you use for HD?

As long as the recoil is similar, I see no problem with practicing with different ammo.

practice with birdshot, but finish up with a few rounds of buck shot.

Of course. I shoot reduced recoil buckshot (and slugs for that matter) and find little to no difference in recoil compared to shooting bulk bird shot (such as the Federal value pack). I do shoot a fair amount of buckshot, especially at training classes. But most of my weekend range practice is with bird shot or slugs.

I tend to play with birdshot as it's much cheaper.

the extra thump from a good buckshot load usually doesn't bother me much.

unless they're 3" Magnums...those have little more punch

About half and half for me. I use reduced recoil OO buck for HD.

I mostly shoot birdshot for practice. It's far cheaper and therefore it allows me to stock up on good HD ammo. I do tend to mix in some 00 buck and perhaps slugs with the birdshot though.

I've never been in a situation where I had to use any gun for defensive purposes, but I think it's safe to say that in such a situation with all the adrenaline you won't notice recoil near as much as you would when practicing.

Nope...I practice with birdshot. Shotguns are point and shoot. I'm not saying there isn't aiming involved, I'm saying pinpoint accuracy it not a big deal with one (get a shot in a torso and you're doing fine...and that's a pretty big target at 8-12'), especially at the short distances found in the home.

With that said...I believe muscle memory concerning the pump action are essential...as it weapon handling. I run cheap-o $22/100rds target loads through mine. I do run 00 buck from time to time in the form of $4/5rds Win military surplus but not the more expensive Hornady TAP I keep loaded in it...it would cost a fortune.