I wonder if they're looking for the hyoid bone? It's not a very big bone (less that an inch), and isn't connected to any other bones in the body. Could it still be somewhere in the streambed, or could it have been carried away by one of the vultures?
I was thinking that maybe the dogs were brought in to search for bones - since reports are that the remains were "scattered" - it's very likely that parts could have been pulled away by animals so maybe they're just trying to make sure that they've collected everything???