Seven Swans could be little bitter sweet. Swans, the largest of the waterfowl and among the largest flying birds are monogamous pairing animals. In fact, while these birds do not reach sexual maturity until they are over four years, they can pair with their mate before they are two years old. So these pair bonds are mating pairs, but they are more than that as well.
I like to think that we are looking at a swan family in this gift with the life long mated pair and the five new hatch lings from the latest clutch. Swans defend their nests, their eggs and their hatchings with fervor seldom seen in birds, and this interpretation really ramps up the true love quotient in this song.
On the Seventh Day of Christmas
My True Love gave to Me,
Seven Swans a Swimming.