Swamped

Even if the bird can help, it looks like it won't pay you much heed until it's done drinking. So you decide to take a look around while it finishes, in case you can get some other lead.

You do see a couple of heavy bootprints in the sand. But only two. Did he dismount and then disappear?

No, you look a little closer. The sand right here is wet. The drier sands wouldn't hold prints as easily, it would only take a modest wind to cover them. You can see faint traces of what might have once been a footprint up ahead.

Rider might not be that far away, then, since the bird's still here rather than returning to its nest. Unless it's a different bird, or it's been drinking for quite a while. You've got no idea how much water this thing needs. Could be it loads up on a week's worth of water all at once or something.

Right now, it looks like you've caught sight of Rider's trail, but you're not sure how to follow it from here. Maybe there's some other sign of his presence that might give you an idea of what to do?