> Within each gender, white-striped birds are more aggressive while tan-striped birds are more nurturing. That seemingly simple generalization is based on a vast amount of research. For many years, Falls and his students at the University of Toronto carried out highly detailed studies of White-throated Sparrows, showing how behavioral differences between the morphs touched every aspect of these birds’ lives.
Why would you define this variation that's associated with behavior "gender"? Isn't the whole distinction between gender and sex is one is biological and the other societal? If there is a hereditary biological indicator that determines this behavior, shouldn't it fall outside of the gender concept? I don't know how useful it is to add these human constructs to the biological world when it could be easily observed and discussed without the confusion