Q. Are geese considered kosher birds for the mitzva of shiluach haken, even if there is no tradition to eat them?
A. Hisorerus Teshuva (4: 155) maintains that a bird that has the simanei or signs of a kosher bird (See Shulchan Aruch Y.D. 82: 3), although if there is no established tradition to eat it, we abstain from it (Rema ibid.), still one should perform the mitzva of shiluach haken as it is possibly kosher. (See similar opinion in Birkei Yosef (292: 10), Shach (ibid.14), Minchas Elozor (3: 43), and others).
Shalach Tishlach (p. 55) quotes that in such a case one should return the eggs or chicks after lifting them to the nest.
Horav Shlomo Miller Shlit’a opinion is similar.
Rabbi A. Bartfeld as advised by Horav Shlomo Miller Shlit’a