They don't 'go' anywhere, they get eaten usually.There are lots of scavengers that will dispose of them pretty quickly. I've seen lots of dead birds over my lifetime, mostly out in the wild..
Also a sick or injured wild creature will try to find somewhere safe away from predators (they have no concept of dying) so many a dense hedge will be the final resting place of a small feathered creature.
Last year a dead pigeon landed about twenty feet from where I stood, at first I thought it had hit the telephone wires but on closer inspection I think it may have been dropped by a Buzzard. Doesn't answer your question I know but I assume this sort of thing must happen quite often.
So you have never seen a dead bird on the street, the park etc. they die everywhere. Quite likely some of the ones ravaged by cats were dead when the cat found them.
My garden I think.
At present I am finding a dead bird almost every week.
I am not near an airport for example.
I have asked a few of my neighbours and they are not having the same problem.
Can anybody help?.
Round my way, pheasants wait patiently at the side of the road for a passing vehicle, so they can run out and throw themselves under the wheels! Plenty of evidence left lying on the roads!
Is that a grouse that you are having, heathfield? We get quite a few folk mowing them down in the lanes around here, a second car behind doing the collection.
Where do birds go during Hurricanes then? Actually, the answer is that they pick up on the approaching storm and will see it out by going for the bottom of hedges for their protection.