How does my dog know where she's dropped her ball?

[jtremlett]

My dog loves playing and especially with a (tennis-sized) ball. But she doesn't bring the ball back, she runs off with it and drops it somewhere. Now we might be in a big grassy field and she'll charge off and somewhere enroute will drop the ball. By the time she stops running about she might be a considerable distance from where she dropped it. However, with encouragement/nagging from me, she can get back to within a couple of feet of where she dropped it. How? One blade of grass looks much like another to me at least. Smell seems unlikely both because the wind direction seems irrelevant but also when she gets close she is clearly searching visually. Do dogs have some kind of in-built GPS? An Internet search seems to either return results about a different of ball dropping or about teaching your dog to bring the ball back.

[jtremlett]

Thank you. I wonder why her nose doesn't take her right up to it? She will get close then start looking around and quite often, with my height advantage, I will actually spot it whilst she is still looking close by. Having said which, she isn't trained at all.