How to tell if the males of your species are assholes

Easy. Their harassing behavior affects the evolution of females. This isn’t sexual selection, it’s just that the juvenile females are disguising themselves with male plumage to escape harassment. These birds, white-necked jacobins, are typically sexually dimorphic, but juvenile females maintain a male-like coloration, because females with adult female coloration face more aggressive assaults from males. Adopting the male coloration allows them to feed uninterrupted, while putting on the sexy female green coat brings on a plague of annoying, obnoxious males.

Ornamentation is typically observed in sexually mature adults, is often dimorphic in expression, and is most apparent during breeding, supporting a role for sexual selection in its evolution. Yet, increasing evidence suggests that nonsexual social selection may also have a role in the evolution of ornamentation, especially in females. Distinguishing between these alternatives remains challenging because sexual and nonsexual factors may both play important and overlapping roles in trait evolution. Here, we show that female ornamentation in a dichromatic hummingbird, the white-necked jacobin (Florisuga mellivora), cannot be explained by sexual selection. Although all males are ornamented, nearly 30% of females have male-like plumage. Remarkably, all juveniles of both sexes express ornamented plumage similar to adult males (androchromatism), but 80% of females acquire non-ornamented plumage (heterochromatism) as they age. This unique ontogeny excludes competition for mates as an explanation for female ornamentation because non-reproductive juveniles are more likely to be ornamented than adults. Instead, avoidance of social harassment appears to underlie this female-limited polymorphism, as heterochrome taxidermy mounts received more aggressive and sexual attention than androchrome mounts from this and other hummingbird species. Monitoring electronically tagged birds at data-logging feeders showed that androchrome females accessed feeders more than heterochrome females, presumably because of reduced harassment. Our findings demonstrate that ornamentation can arise purely through nonsexual social selection, and this hypothesis must be considered in the evolution of not only female-limited polymorphism but also the spectacular ornamentation often assumed to result from sexual selection.

They’re evolving to be able to eat dinner in peace.

Boy birds should be ashamed of their behavior, is all I can say. They can’t even leave a taxidermy dummy alone!

Falk et al., 2021. Male-like ornamentation in female hummingbirds results from social harassment
rather than sexual selection. Current Biology 31, 4381–4387.


  1. StevoR says

    They can’t even leave a taxidermy dummy alone!

    Do you think those evolutionary psychology types will come up with a Just-so story about the evolutionary advantages of necrophilia using that fact now?

    FWIW I gather cane toads are known to copulate with dead cane toads too.. Dunno ’bout lobsters..

  2. says

    They’re evolving to be able to eat dinner in peace.

    If natural selection is favoring females who can avoid male harassment, that kind of implies that the males’ habits of harassment are doing more harm than good to the species’ ability to reproduce; otherwise it would be the aggressive males and their chosen targets out-breeding the non-targeted females, right? There’s a lesson our species’ frat-boys won’t want to hear…

  3. silvrhalide says

  4. steve1 says

    Reminds me of when a major theme park had to change the Pocahontas costume becuase the women in the costume kept getting hit on.

  5. skeptuckian says

    How to tell if the females of your species are assholes

    Females will only mate with males that have elaborate ornamentation and/or engage in embarrassing dances that lead to higher rates of predation or with males that are willing to engage in (sometimes) deadly and injurious combat.

    Mating systems are fascinating to study from both an ecological and evolutionary viewpoint. I do recall that the overall investment in mating and offspring production evolves to be equal between the sexes. Sexual selection and evolution just keep the hits coming!