The sentence suggests something is killing the animals, and leaving the dead bodies of the animals behind where ever it goes. "Trail" could mean a path where people or animals often walk on, but in this case, a lot of bodies in a straight line could also suggest these bodies are marking and indicating the direction of a killer. You can also see a variation in another sentence, "leaving a trail of bread crumbs behind". It suggests someone is dropping small bits of information to show where they are walking to.

Actually, I had another thought about your question. Yes- the two sentences are the same. It is because the subject is the killer, and what it leaves behind. Whether the sentence says the dead animals are left behind the killer, or the killer left behind dead animals, it all means the same. The only difference I can think of, is that in the first example, the dead animals are mostly dead deer and small animals like rabbits, with the possibility of other small animals (the size of a deer or smaller). In the second example, the dead animals are only deer and small animals like rabbits (which suggests those are the only two animals you will find on the trail). The change in meaning is quite subtle, and it wouldn't be very different unless you really think very hard about it.