O Lakshmaṇ, many a time we see Great souls who keep the law’s decree, With whom the weak sure refuge find, In creatures of inferior kind. The loss of her, my darling queen, Strikes with a pang less fiercely keen Than now this slaughtered bird to see Who nobly fought and died for me.

In plain words: Rama says that even among animals we often find great, good souls who follow what is right and protect the weak. He says that seeing this bird dead hurts him even more than losing Sita.