If it happens in nature, does that mean it's natural?

If so... then, same sex coupling/parenting is natural. According to this article, "nearly one-third of the 125 pairs [of the albatross in a colony under observation] consisted of two unrelated females, and half of these stayed together for the duration of the study."

Of course, this study says nothing about the sexual desire of the birds, if birds even have sexual desire. It just says that it's perfectly natural for two females to form a bonded relationship and co-parent.