akuperma,
1. It is a “proof” we can bring when arguing with frei Jews that Humash is not a later forgery attributed to an earlier period, since if that were so it would certainly contain references to what became the most common domestic fowl among Jews. Chickens were common by the end of Bayis Rishon (when the apikoresim say Humash was written), but not prior to the period of the shoftim (i.e. not during the time of us being in the midbar).
I think you mean secular biblical scholars and not frei Jews. If you ask a typical frei Jew when the Torah was written, he’d say, “beats me!” It’s an interesting point, but I don’t think it would make any difference in a debate.
2. It suggests that the concept of a “mesorah” (tradition) as to which birds are kosher has always been flexible (bad news for turkeys and braekel/heirloom chickens hoping for long lives). Usually when we talk about halacha based on a mesorah, we mean a tradition going back to Sinai, but for birds it suggests a tradition reflecting the consensus of earlier generations of Bnei Torah (turkeys to the early achronim, chickens to the period of the Shoftim and Bayis Rishon).
We have to rely on a mesora of kashrus for bird species now because we can no longer definitely identify the non-kosher bird species that the Torah lists. I think it’s safe to assume that Jews living in the Bayis Rishon period knew the non-kosher bird species definitively, and therefore could eat chickens because they knew they weren’t on the list.