Backyard bird has a lot to teach us about sex variability

For example, there are fish where it is the male that exclusively protect and manage the eggs. As such, the male expends more energy than females, or to use similar terminology as I did before, the males in that situation expends more energy on their reproductive strategy during reproduction than females. All that the females do is produce the eggs and then leave. It not unreasonable to predict, using tournament species theory, that the female is physically larger than the males, and the male being the one that choose which female they accept. This also happen to be what we generally can observe with such fish.

So what sex should we describe them as? Should we then call the males as Juliets, and females as Romeos? Should we describe the males as being feminine and the females as masculine?

Different schools and cultures will find different way to look at things. The article focused on genes, and specifically those defined by sex chromosomes and those that were not. The words they use are sex-related traits and genes associated with sex, in order to describe how traits and genes can then go and provide a variability in sex, while acknowledging that most of those genes are not associated with sex chromosomes.

In the end it is multiple people looking a the same thing finding different theories and producing tests and predictions to test them. I personally view the article as being a bit too liberal in their anthropomorphism, attributing human behavior to that of animals in order to make connections between the two. I would not use the word masculine to describe a fish or a bird, or to describe it as sex variability in order to explain why their behavior is different from the expected human male or human female. Sex identification of animals is diffused enough that its only a rough approximation to what kind of gonads that they have, and in some cases that is not meaningful distinction and we can't actually make an identification.