Shuchan Aruch Yoreh Deah 292:1 rules that the commandment of shiluach haken applies only to birds which are tahor, a kosher species. The meforshim explain that the Torah say tzipor which only refers to kosher birds.
Most birds are, technically speaking, kosher (or of a kosher species/tahor). The Torah lists 22 some odd exceptions which are prohibited but insofar as we do not have a mesorah (tradition) identifying the 22 un-tahor birds we only eat birds which have an affirmative tradition that they ARE kosher/tahor.
If one chances upon a bird which does not have any of the simanim (indicators) which Chazal associate with a non-tahor bird but which we do not have an affirmative tradition that they are kosher, does one fulfill the mitzvah of shiluach haken?
In other words according to those who rule that one MUST send away the mother bird even if one doesn't need the eggs/chicks is one obligated to do so when one finds a potentially tahor mother bird?
Or according to the other authorities if I have a need for such eggs (other than to eat since they are forbidden because of their questionable status) am I obligated to send away the mother bird even though she may not be kosher?
Aren't these cases where we say safek d'Oraisa l'chumrah, conversely similar to our being strict not to eat them?