The white-necked Jacobins or large-collared Jacobins ( Florisuga mellivora ) are hummingbirds that live in the center and south of the American continent. They are a species with a clear sexual dimorphism, that is, males and females have a very different appearance. The males are characterized by having a white neck and a metallic blue head, while the females have an olive green head and less surface of white plumage on the chest.
However, this coloring pattern is not always the case. In 1950 it was discovered that approximately 30% of females acquire the typical plumage of males upon reaching adulthood . Although the researchers do not know if the reason for this variation is genetic or environmental factors, they have tried to investigate the ecological function that this alternative coloration could have.
Recently, a group of American scientists has published their experiment in the journal Current Biology . Between 2015 and 2019, they observed the social interactions of 436 white-necked Jacobins and discovered that, especially when feeding, males tended to boycott females: they had aggressive attitudes against them, such as pecks and blows, which prevented that they could eat with peace of mind. However, this was not the case for those that enjoyed the same coloration as the males. They could eat many more times and for longer than those of classic coloration, since the males did not scold them. They had a social advantage.
Seeing this fact, the researchers wondered if the alternative coloration of the females had any effect when it came to mating. By experimenting, they found that males always preferred classical-colored females. In an interview for the newspaper El País, Jay Falk, professor in the Department of Neurobiology and Behavior at Cornell University and co-author of the study, affirms that “it is difficult to say if the mating advantage for female-looking females is really something. they care. In our experiments we saw that, although they had an advantage in attracting their mates, females with the colors of the males were also courted ”.
Scientists are betting on a social selection, which unlike sexual selection, consists in that the appearance and defense systems of living beings evolve as a function of competition for food, partners or the attention of parents.
“The study really shows that you have to think broadly outside of sexual selection to have a full understanding of why certain birds are colorful and others are not. We have studied a species that probably does have sexual selection in males, but even so, this does not provide a complete history of ornamentation, especially when it comes to females, “concludes Jay Falk.
References:
Falk, J. J., Webster, M. S., & Rubenstein, D. R. (2021). Male-like ornamentation in female hummingbirds results from social harassment rather than sexual selection. Current Biology. Published. https://doi.org/10.1016/j.cub.2021.07.043
