Over any given year where I live there must be thousands of birds fly over, take up temporary digs whilst migrating or live within a territory they have staked out in which my humble plot of land exists. Why do dead birds not litter my land and the local parks? Cockatoos are blessed with long lives whilst the smaller birds such as finches and wrens are supposed to be relatively short lived (they were when I used to breed them.) Over the last ten years I have seen two (2) deceased avians. One was a parrot in the local park and the other a juvenile butcher bird which I witnessed being attacked by other local birds. Why is it so? Are there places scattered around the world where birds go to die? Is there an ornithologist in the house?
A couple of thoughts from an ameteur birder (but not an ornithologist, still less a twitcher). The ones flying over are pretty healthy, as are the ones you see staking out territories. Ill and infirm birds will tend to hide where predators can't see them, such as in thick undergrowth. Also dead birds don't tend to last long. Generally predator birds and rodents dispose of them quickly. They also decompose very quickly, bones and all, as the bones are mostly pretty fragile. Having said that, I reckon to find 3 or 4 dead birds a year in my ordinary suburban garden, and that doesn't count the drifts of feathers left when our local sparrowhawk has caught another little bird too intent on one of our feeders to keep a proper look out.
Salient points, INJ, I have no doubt. Ants too can do a very efficient demolition job on a carcass, but I doubt (in fact would reject) the idea that bird feathers are nutriment for scavengers. The reason for that attitude is that individual feathers, presumably resulting from natural 'moulting', are common and most certainly not a part of a drift of feathers produced by either direct attack or the efforts of scavengers. Who hasn't come across a particularly attractive feather from time to time and wondered what type of bird lost it?
[Dujon] Indeed, I'm sure that in your neck of the woods ants will be particularly efficient at cleaning up. I agree feathers are a bit different, but they must be destroyed fairly quickly if only because otherwise we'd be up to our necks in them. Also they are pretty much pure keratin which, despite its toughness, is none the less protein and so crying out to be recycled. I'm now into speculation, but I would suspect insects & bugs are likely to be the cleaning crew and will reprocess the feathers into chitin etc. Surely there's someone in the morniverse who can add a bit more scientific rigour at this point.