Mishnayos Beitzah Perek 1 Mishnah 3

Beit Shammai say: One may not carry a ladder, which was used for reaching doves, from one dovecote to another. However, one may move it slightly so that he tilts it from one window to another in the same dovecote. And Beit Hillel permit even carrying a ladder from one dovecote to another. Beit Shammai say: One may not take fledgling doves from a dovecote on a Festival, unless he shook the ones he wished to take while it was still day, thereby preparing them. And Beit Hillel say: It is not necessary to shake; rather, it is sufficient if one stands the day before and says: I will take this fledgling and that one.