Why the fixation with birds in the ‘12 Days of Christmas’?

Half of the days in the traditional holiday song “The Twelve Days of Christmas” are devoted to birds. That strikes me as interesting.
In fact, the first four items are birds. “The Twelve Days of Christmas” is an English Christmas carol that recounts a series of increasingly grand gifts given on each of the 12 days of Christmas. The carol dates back to 1780, a Wikipedia article states.
According to the song, the recipient of the gifts would have received one partridge, two turtle doves, three French hens, four calling birds (originally it was “colly birds,” with “colly” being a regional English expression for “black”), six geese and seven swans. That’s 23 birds.
I can only assume that these birds are gifts of food, since they all were commonly eaten back then.

Art: “The Twelve Days of Christmas” song poster by Xavier Romero-Frias.