Leviticus 11:13-19 has a list of non-kosher birds that match a list in Deuteronomy 14:11-18 (NJPS):
You may eat any clean bird. The following you may not eat: the eagle, the vulture, and the black vulture; the kite, the falcon, and the buzzard of any variety; every variety of raven; the ostrich, the nighthawk, the sea gull, and the hawk of any variety; the little owl, the great owl, and the white owl; the pelican, the bustard, and the cormorant; the stork, any variety of heron, the hoopoe, and the bat.
My casual reading of both passages is that any bird not listed in these passages is kosher. (Which means birds that weren't known to Moses such as turkey and emu would be considered clean.)
But the odd thing is that the other types of animals are divided based on certain physical characteristics. So verse 3: "any animal that has true hoofs, with clefts through the hoofs, and that chews the cud—such you may eat." Verse 9: "These you may eat of all that live in water: anything in water, whether in the seas or in the streams, that has fins and scales—these you may eat." Verse 21: "But these you may eat among all the winged swarming things that walk on fours: all that have, above their feet, jointed legs to leap with on the ground." So if you find a new species of land animal or fish or insect, you can apply the rules and get an answer about whether it's kosher.
What's going on with the list of birds that makes providing distinguishing characteristics unnecessary?