"fledglings or eggs,": I would understand: the minimum of "fledglings" — two; the minimum of eggs — two. Fledglings have a purpose and eggs have a purpose, to exclude dead fledglings and winnowed (non-viable) eggs, for these have no benefit. If there is only one chick or one egg in the nest, he must send, for it states "if there chance before you a bird's nest" - in any event.)
"on the way in any tree or on the ground": on the way is in public property, excluding if they were tied up.
[Variantly: "Send": Scripture speaks of a clean bird. — But perhaps it speaks of an unclean bird too? It is, therefore, written (Ibid. 14:11) "Every clean bird you may eat": This is a prototype, viz.: Wherever "bird" is mentioned in Scripture, a clean bird is understood (unless specified otherwise) as R' Yoshia has stated. If after sending he turned his face away from it he is exempt from sending further.]