.י Birdie Care

אמר רב חנן בר אמי: מחלוקת בבריכה ראשונה, דבית שמאי סברי: גזרינן דלמא אתי לאמלוכי.

רש"י ד"ה בריכה ראשונה - דרך מגדלי יונים להניח בריכה ראשונה של כל שנה להיות צוות לאמה: 

גזרינן - כי שקיל להו למחר אתי לאמלוכי וחייס עלייהו והוי ליה טלטול שלא לצורך ומשנענע ומשמש בהן מבעוד יום לשחיטה ולא חס עלייהו תו לא חיישינן דחייס:

If we accept רש"י's initial explanation as to why the general approach to בריכה ראשונה would be different, perhaps we can offer an alternative explanation as to why בית שמאי would require you to pick up the birds before יום טוב. The whole purpose of leaving the first group of birds is to accompany the mother. However, there seems to be a general idea that a mother bird will not return to its nest if it senses that it has been tampered with by human hands. For this reason, those performing שלוח הקן are careful to use gloves so that they can put the eggs back and other individuals can then perform the מצוה as well. רש"י is saying that the mere act of handling the birds is indicating that he is not going to have pity and leave the birds later to be with their mother. But perhaps the reason handling the birds before יום טוב is significant is because the mother will then no longer return to the birds and you have already defeated the purpose of leaving the בריכה ראשונה.

It should be noted, however, that the Star-K consulted with bird experts for their article on שלוח הקן. According to the Cornell Lab of Ornithology, it is a common misconception and most birds are not actually capable of accurately detecting human tampering and will still return to their nest. Still... something to think about.