The jays move the semps around for one of two reasons... They buried a nut or other food item close to it (even under it) and they have come back to retrieve it, or they are using the semp (presumable small one) to cover a place nearby where they have buried a nut (food). They are very smart birds. If they think another jay has observed their cache they will dig it up and move it to another place.
Signed, Connie who spent a good year or so closely watching these birds.
