Petrified Bird in our Backyard?

There I was, raking leaves in the back yard when I saw what I thought was a black slug in the tree. I tapped it with the end of the rake and was very surprised that it was very hard. I thought, "Hmm, that's odd." I went in for a closer inspection and was a little disgusted when I noticed an eye. Then it dawned on me, "Oh no it's a bird. It must have died in the tree. Man, those Arizona summers must have been really brutal on this guy 'cause now he's petrified!" I quickly called for Michelle to gross her out. I went and got the camera and snapped that shot. Only then did I stop to think: "Wait, is that even possible?" I began to suspect there was some flaw in my logic, so I cleared away the leaves that were surrounding the bird and discovered some string and a "crack" in the bird, revealing it to be nothing more than a plastic shell. And if you look closely at the picture, you'll notice the plastic just below the beak. It had us fooled for a couple minutes though. It was put there a long time ago because the tree is starting to grow around it.