Have you ever looked up and seen a flock of hundreds if not thousands of birds? With the billions of birds around, why don’t we see yards and roads littered with bird carcasses?
The answer is actually quite simple; predators. Nature continues to go on just as it always has by survival-of-the-fittest.
I’m sure you’ve seen the occasional road-kill and circling or hovering about were crows or vultures just waiting to get at it. Small animals get snatched-up so fast by others that even if you walk through the woods, you probably wouldn’t see anything lying around except for something larger like a deer which would take longer to be consumed.
If other animals weren’t bad enough, there are always beetles, maggots, etc. that can work incredibly fast to consume anything lying around.
Also, birds are not likely to just drop out of the sky. Just like any living creature, if it’s ill (or some can sense when they’re dying) they’ll “go home” or somewhere else to rest. Often, predators can even sense when another animal is ill or weak and attacks even before it dies naturally.
So, I guess we should be kind of grateful that nature cleans-up after itself.