Is it necessary for your dog to come to a halt and scratch the lawn after doing his business? While it may appear that he is acting strangely, he is methodically claiming his territory, letting all other dogs know that he was the first to arrive.
Many people believe that dogs are attempting to clean up after themselves, which is why they act like cats around poop. This would seem to be the most obvious answer, however, this action carries far more information than simply cleaning up. Scratching dirt and grass is an instinctive action that has historically kept dogs alive. They could extend the line and eat well because they were protecting food and ensuring the girls' safety. Their instinct is to mark their territory and signal other dogs to leave them alone.
Yes, they are responding on instincts, which is a natural behavior. Wolves and foxes may exhibit similar behavior if you spend time in the wild. Like our tamed dogs, they would scratch the dirt after pooping. This behavior can be seen in various breeds, however, not all dogs will execute this "ritual."