Deuteronomy 22:6 "You shall not take the mother bird together with her young"

This Negative Mitzvah teaches us the proper way of taking eggs or young birds from a nest (see Positive Mitzvah 148).

We must first send the mother bird away because we are not allowed to take the young while the mother bird is still in its nest.

We are also not allowed to take the mother bird at the same time we take the young.