If you visit the beach or a large metro area you’re sure to come across a dead seagull or pigeon.
But I live in a residential area with a zillion birds flying around. Yet I rarely see a dead one on the ground. And then it’s probably from getting struck by a car.
Where do all the old birds go when they croak?
In various animals’ stomach.
A search should turn up previous threads. Short recap of my answer: I see dead birds a fair amount. They get eaten pretty quickly, usually by ants.
I have woods adjacent to my house and put seed out for the birds, so lots of birds chez chiroptera. I occasionally see a dead one but it’s invariably gone within 24 hours, feathers and all.
The Master Speaks: http://www.straightdope.com/columns/read/984/where-are-all-the-dead-pigeons
I love that article. “Wow, now it sings.”
To sum up some of the information in the links and previous threads:
Most birds end up as a meal for predators. Few die of natural causes.
If a bird is sick or starving, it will usually take refuge in a secluded place such as a hole or roost, where you won’t see the body if it dies.
Most birds only weigh a few ounces. If they die in an exposed place, the body is usually only going to last a matter of minutes or at most a couple of days before some scavenger scarfs it up or it’s eaten by ants or maggots. Corpses of larger animals may take several days to weeks before they disappear.
I always thought it was like the elephants. There’s a legendary bird burial ground where they fly off to die when they’re near death. You don’t find a lot of elephant skeletons in Africa (now mainly because there aren’t a lot of elephants left), but that was believed becase even elephant remains were rapidly eaten and dispersed. Somewhere I saw time lapsed photos of elephant remains that were eaten and scattered within a few days.
In addition to the above, I’m going to add a speculation. Most birds are, to some extent, migratory, and I suspect that a majority of the mortality occurs during the rigors of migratory movements, which weeds out those individuals not strong enough to make it. The demise of these victims would highly likely be in the vast uninhabited reaches of the territory they fly over.
Those “zillions” of birds that you see in your neighborhood are the hardy ones that have survived that ordeal, and those among them who die while merrily chirping in a tree represent a very small fraction of the non-survivors.
I live in a residential neighborhood. We don’t have wolves and foxes running around.
Though I suppose one could include an outdoor pussycat as a member of the Wild kingdom. 
I came across two dead owls this summer while walking in the woods. Not the same day.
As well as no insects?
Almost any non-urban place in North America (and some urban ones), if you go out at any time and scan the horizon with binoculars, there is a good chance you’ll see circling Turkey Vultures, which will fairly quickly gobble up the remains of any dead crittur. I see them in trees in my residential neighborhood, patiently watching something die.
I imagine you have dogs, cats, raccoons, and maybe skunks and rats. Also crows, jays, maybe Red-tailed Hawks, possibly Kestrels. Some may not catch birds very often (neither would wolves or foxes) but they would make short work of one that was injured or freshly dead.
Yes, here we see crows and hawks often picking a carcass. Probably other animals at night though.
… possums, too.
Fine, but it’s not like we have those creatures patrolling the neighborhood in packs.
One would think we’d at least see the dead birds on the ground during the day before the buffet started on it.