“ But if there are only those particular birds (that he designated i.e. he designated white ones and he could only find black ones) these are allowed.
1:5
Beis Shammai says: one may not remove a door (cupboard door? see Beitzah 11b) on a festival Beis Hillel permits it, except for putting it back. Beis Shammai says one may not crush meat with a pestle on a festival. Beis Hillel permits. Beis Shammai says one may not place a hide in the path of tramplers, (i.e. using it as a doormat) and one may not lift it up, unless with it there is an olive's volume of meat. ”