“Conspicuous plumage does not increase predation risk: A continent-wide test using model songbirds”
Kristal E. Cain, Michelle L. Hall, Illiana Medina, Ana V. Leitao, Kaspar Delhey, Lyanne Brouwer, Anne Peters, Stephen Pruett-Jones, Michael S. Webster, Naomi E. Langmore, and Raoul A. Mulder (Mar 2019)
The DOI will be https://dx.doi.org/10.1086/701632
Colorful feathers don’t attract predators. Bright and cryptic 3D birds are attacked equally across 8 Australian sites
Birds can be incredibly colorful or incredibly dull, but we still have a poor understanding of why. A recent bit of research from Australia has made the story even more interesting by undermining a long-held assumption about the costs of being bright.
Previous research has shown that both males and females can benefit from being bright, especially when they have to compete for important and limited resources (mates, territories, nest-sites, status, etc.). If that is true, why are so many birds brown and dull? The most straightforward explanation is that it is dangerous to be bright; being bright makes it easier for a predator to spot you. For many years, researchers have assumed that differences in predation risk probably drive some of the observed differences in bright colors.
To test this assumption, a group of biologists based in Australia looked at how color and predation risk are related in fairy-wrens, a group of small songbirds that live in a wide variety of habitat and vary from dull brown to bright blue. They 3D-printed model birds and hand-painted them to represent bright and dull males and females. Then they put them out them in fairy-wren habitats all over Australia to see which models the predators attacked and which they ignored.
To their great surprise, they found that the dull models were attacked just as often as the brightly colored models, and in some cases, even more often. These results suggest that, all else being equal, being brightly colored does not increase the chances that a predator will attack.
Instead, the authors suggest that the relationships between predation and color are not nearly so simple as we thought, and more research is needed to understand differences in color.
The forces shaping female plumage color have long been debated but remain unresolved. Females may benefit from conspicuous colors but are also expected to suffer costs. Predation is one potential cost, but few studies have explicitly investigated the relationship between predation risk and coloration. The fairy-wrens show pronounced variation in female coloration and reside in a wide variety of habitats across Australasia. Species with more conspicuous females are found in denser habitats, suggesting that conspicuousness in open habitat increases vulnerability to predators. To test this, we measured attack rates on 3D printed models mimicking conspicuously colored males and females, and dull females, in eight different fairy-wren habitats across Australia. Attack rates were higher in open habitats, and at higher latitudes. Contrary to our predictions, dull female models were attacked at similar rates to the conspicuous models. Further, the probability of attack in open habitats increased more for both types of female model than for the conspicuous male model. Across models, the degree of contrast (chromatic and achromatic) to environmental backgrounds was unrelated to predation rate. These findings do not support the long-standing hypothesis that conspicuous plumage, in isolation, is costly due to increased attraction of predators. Our results indicate that conspicuousness interacts with other factors in driving the evolution of plumage coloration.