Exploring the evolution of female ornamentation
Due to their isolated nature and unique species, remote islands are valuable natural laboratories for studying the intricacies of evolution. One particular trait affected by island life is ornamentation – decorative characteristics that attract mates and are often linked with sexual success. Historically, research into birds has focused on male ornaments as they are conspicuous: think bright plumage or elaborate songs. Yet in tropical regions, female ornamentation is also common – although relatively understudied. “Female traits such as song and colourful plumage are not only present but likely ancestral in songbirds, suggesting that female ornamentation has evolved under direct selection pressures,” explains Ana V. Leitão(opens in new window), postdoctoral researcher at CIBIO. “Females, like males, may benefit from ornamentation in contexts like competition for mates, nest sites or social dominance,” she adds. To revise this historic bias, Leitão studied changes in female and male ornamentation in the EU-funded EvoColorIsla(opens in new window) project, to understand how island colonisation might influence its evolution.
Comparative analyses and targeted field experiments
First, Leitão co-curated a comprehensive dataset including all island endemic(opens in new window) species and their closest continental relatives, and expanded it during a research visit to the Naturalis Biodiversity Center(opens in new window) in the Netherlands. There she collected additional plumage data from preserved bird specimens and researched existing academic literature. “This allowed me to examine patterns of ornament expression across species in both mainland and island environments and to assess how different factors may have influenced the evolution of colouration,” she explains. In parallel, Leitão ran a series of experiments in a fieldwork campaign that stretched across Madeira, the Azores (São Miguel) and the Canary Islands (Tenerife and Fuerteventura), as well as mainland Portugal. These experiments sought to understand how animals perceive in nature. For 12 species – six pairs of island birds and their closest mainland relatives – she created life-sized 3D-printed models of the birds based on real museum specimens, which she then hand-painted and colour-validated using spectrophotometry and visual modelling. Some experiments tested whether island birds were threatened less by predators, and others explored behavioural responses to female and male model birds, to see how social and competitive interactions vary between islands and the mainland.
Colourful preliminary results
One key finding was that island birds appear to be under less pressure from predation than those on the mainland. Preliminary results also suggest males and females reacted differently to the presence of putative ornamented rivals, pointing to a potentially sex-dependent role of ornamental traits in social interactions. Meanwhile, in some species, females retain or even increase their ornamental traits, suggesting they are actively selected – potentially by reduced predation or increased social competition.
Broadening knowledge on island ecology
“I hope these results will contribute to a more balanced and inclusive understanding of trait evolution by highlighting the role of both sexes, particularly in systems like islands, where conditions often differ significantly,” says Leitão. More broadly, the research challenges long-standing assumptions, such as the idea that elaborate traits are primarily male-driven or maladaptive in females – rather, they can be functional and subject to selection. “These insights can inform both evolutionary theory and conservation strategies, especially when managing isolated or vulnerable populations in ecologically unique settings,” notes Leitão. She is now applying for further funding to extend the research to the evolution of female songs on islands.
