Chullin 139: Required to Find a Mother Bird and her Offspring?

Yesterday's Mishna began discussion about the Torah law forbidding taking eggs or chicks without sending away the mother bird first (Devarim 22:6-7).  Today the Gemara explores the words that introduce the mitzvah, "If a bird's nest happens before you on the way..."  The rabbis recognize that it is a positive commandment to send the bird away, there is no requirement to search for a nest.  Only if one happens to come across a nest does the mitzvah apply.

Rabbi Yair Chaim Bachrach argues in his responsa, Chavvot Ya'ir, that if one comes across a mother sitting on her eggs or her chicks, he would be required to chase away the mother and take the offspring even without any use for them.  This is because the Torah directive does not free a person from the obligation to fulfill the positive mitzvah.

The Chazon Ish argues that we are meant to search extensively to ensure that one might complete this mitzvah.  His argument is that the Gemara is is only using this passage we would have assumed that everyone is required to perform this mitzvah at least once in his or her lifetime.  Searching would be necessary.  

In the end, the rabbis determine that the mitzvah is only obligated on someone who truly wants the eggs or the chicks.