How long does it take for a buried animal carcass to fully decay to just bones?

2 months ago I was in my backyard and found a dead bird (no sign of trauma, just looked like it dropped dead). I already had a shovel handy so I just made a hole next to it, scooped it in and buried it. Now I'm thinking of restarting my vegetable garden, but it's right where I buried the bird. I don't want to dig up a half-rotten, wormy carcass, so when would it have decayed to only bones?