Wild turkeys are virtually always seen, and invariably photographed, standing tall and proud with their heads up. But if you see them a lot, as we do out where I live, once in a while you'll see them crouched down with their heads low. And if you see that from a distance, what you end up with is a brown, oval shape that's very similar to the shape of a turtle.
Once while going out to look at a piece of land, I saw in a distant field maybe twenty or thirty turkeys in this position, none of them moving. At a quick glance, the impression I got was a field full of turtles, which is not something you normally expect to see. Then again, neither do you expect to see thirty turkeys without any visible heads. So for a split second I started to say "Hey, are those turtles?" or something like that, but by time I finished saying it, I was already correcting myself.
Still, Siobhan was amused. And though she got what I meant about how they could look like turtles in that situation, she still made fun by calling them turtle birds whenever we saw them, and that stuck, so that's all we call them now.