I am not sure that I can shed much light on the question, as my personal focus in writing has been the variability of sexual behavior and expression in both the plant and animal kingdoms. I do not profess to be an expert in human gender studies.

That much said, it seems to me to be a bit premature to simply say that gender is a social construct, case closed. There are several theories that purport to explain gender development and identity, and considerable ongoing debate among scholars in the field. If there is a consensus in the literature, I haven't seen it--but again, that isn't a specialty of mine.

I am struck by the fact that we have documented partial sex changes among both birds and mammals (that is, phenotypical changes in adult animals that mimic the opposite sex) and these are accompanied by changes in behavior patterns that align with those phenotypical changes. Are those changes in behavior patterns gender changes?

I suppose that it depends on your definition of gender, which has evolved over the past couple of decades. This is particularly true among feminist scholars, who have pioneered the distinction between gender (as a social construct) and sex (which is biology). Of course, many in the general public continue to use 'gender' as a synonym for sex. The only thing I can say with certainty is that sexuality across the plant and animal kingdoms is surprisingly diverse and clearly defies the simplistic assumption on the right side of the political spectrum that it is always binary.