Gender expression is a psychosocial phenomenon, whereas bioscience defines maleness and femaleness strictly in terms of gamete production. That's why male seahorses are still considered male and female hyenas are still considered female even though their behavior and anatomy are both opposite from what one would generally expect.
That said trans type behavior is observed naturally occurring in the social systems of other creatures, such as many male Salaria pavo specimens observed exhibiting the behaviors and coloration of the females of their species. However from a scientific standpoint these are still nonetheless considered to be male
What science? Gender expression is a psychosocial phenomenon, whereas bioscience defines maleness