Ornament, Armament, and Aggression: The Forgotten Beauty of Females

On a warm summer morning in 2023, a group of naturalists tread a trail in a forest buzzing with chirps and tweets. With alert eyes and attentive ears, they inquisitively record the frenzy of birdsong around. It was the season when the male birds brought out their best colours, charms and melodies to win over a potential mate. They engage in elaborate displays of showmanship in an attempt to impress a drab-looking, dull-coloured, passive female.

While scanning the tree branches, the naturalists notice something unexpected. A bird chimes a sequence of notes, seamed together as an elegant song. This odd artist, however, is a female bird, not a male. But how is that even possible? Female birds do not sing, so this must be an anomaly. Aren’t all of these delightful songs, eye-catching colours, and menacing horns a male prerogative?

The common notion that beautiful songs and dazzling colours are restricted to male birds is not true. Female birds can sing, like male birds, and may also have many elaborate sexual features long thought of as male-exclusive. In fact, in several biological systems, it’s been recorded that females are not that passive after all!

 

Why, then –– if they are so common –– have we, for so long, turned a blind eye to female sexual signals? A blend of history, societal perceptions of women, and their eventual impact on science sheds light on these biases. The ground-breaking theory of sexual selection proposed over 150 years ago, posited that males are competitive and females are choosy. The cultural and societal views of women and gender stereotypes of the time shaped this idea. It dictated, almost axiomatically, that any showy, competitive, or aggressive features belonged solely to males. Subsequent scientific explanations proposed by Bateman (1948) and Trivers (1972) further built on and expanded this idea. The higher energetic investment that females devote towards reproduction and parental care stood to legitimise the “choosiness” of females or their lack of showiness and competition.

These ideas led to a generalisation across the biological world, making physical displays and “fighting” the sole domain of males. If the females of any species did show elaborate adornment of the sort, it was attributed to genetic correlation, i.e., since males and females have similar genes, the eye-catching features of females existed only because they are present in males. This argument provided a firm denial of any female decoration, which was regarded as non-adaptive and a rudimentary expression of male traits. For years, female birds were viewed through this lens, inhibiting scientific inquiry or even scrutiny.

The biological world has plenty of examples of “flamboyant” females. From eye-catching colours and pleasant songs to direct aggression, dominance assertion, and fights –– these quirky traits and competitive tendencies are not limited to females of any particular species. Females of several taxonomic groups often use these secondary sexual characteristics to attract a male or confront other females.

The wattled jacana represents a classic example where females compete fiercely among themselves by maintaining and defending territories. They represent a polyandrous mating system where females mate with multiple males, and the males are primarily responsible for incubating eggs and rearing the chicks. The female two-spotted goby fish develop a colouration on their belly, which the males assess while choosing their mates. This example is particularly interesting, as gobies represent a polygamous mating system, where males mate with multiple females, representing the conventional system upon which ideas of competitive males and choosy females are based. Females frequently use visual displays and colours to confront other females, as seen among rock agamas.

Birdsongs, which were predominantly considered the authority of male birds for decades, were found to be widespread among female birds as well. In troupials, a monogamous species, i.e., females and males pair for life, and both sexes sing and defend their nests from competitors.

In many species, dominance and fights among females have been observed. Aggressive confrontations between females are commonly seen in group-living and cooperative breeding meerkats. Female Soay sheep and a species of dung beetle possess horns, which they frequently use for combat.

The marvels of female adornment and aggression do not end here. A vital question remains: what factors determine the development and evolution of such flashy features in females? Across species, the presence of embellishments in females can range from being completely absent to a reduced version of what males have and, in some cases, just as extravagant as the males. In many species, these features can also be more pronounced or completely different than in the males. The current evolutionary understanding of sexual selection can almost entirely explain male traits and tendencies. Female extravagance, however, does not completely fit into this narrative and appears to be more complicated. Females likely employ these traits and techniques to compete for the resources necessary for successful breeding, in addition to using them to attract or defend a mate. The full gamut of explanations behind female beauty, therefore, remains a mystery.

Research on female behaviour and ornamentation, though in its infancy, has challenged many of our traditional sex-exclusive scientific perspectives. Interestingly, female scientists are at the forefront of this change. This is well exemplified in the field of bird vocal behaviour, where female scientists have driven discoveries and research of female birdsong, as found in a study by Casey D Haines and others published in the journal Animal Behaviour in 2020.

Historically, the pursuit of science has been led by men. Comprehending the complexities of sexual selection and behaviour predominantly from a male perspective has likely led to biased discoveries of the biological world. Increasing the representation of women in scientific discourse can be the first step towards changing the way we have looked at these fancy forays in the sexes so far. More diverse groups of researchers contributing their insights will develop new perspectives, methods, and outcomes and enable the deconstruction of inadvertently sex-biased scientific ideas.