When they leave the tree easily if you put your hand under the pear and raise it slightly. I don't think Williams store all that well. They tend to ripen on the tree and need to be eaten or preserved ASAP. At one time we had a large Williams pear. In a good year we left them in boxes on the front wall and they all went very smartly. I used to preserve quite a few jars in those days....not all that difficult.