Fan Casting Animal Gender-Bender in Sort by Tropes

Animal Gender Bender is when all members of an animal species are shown to have a well-known attribute of that species, but in Real Life, only the male or female normally has it. So you end up with male cows, male blood-drinking mosquitoes, female lions with manes, red female cardinals, male goats with udders, male bees with stingers, female moose with antlers, male calico or tortoiseshell cats, female roosters, male kangaroos with pouches, and so on. Barring the theory that perhaps these characters are meant to be transgender, intersex, or otherwise an anomaly of some sort, it's best to assume that this is pure artistic license.