"You shall not take the mother-bird": a negative commandment. "Send, shall you send away the mother-bird": This is a positive commandment. If he sent her away and she returned — even four or five times — he is obligated to continue sending her, it being written "Send shall you send." But if he sent her and she returned to his hand, he is exempt from sending her again....
(Geese and hens that rebelled (i.e. flew away) and nested in an orchard — must be sent. If they nested in a house — one is exempt from sending.