Browsing by Author "Kempenaers B"

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    Evolutionary predictors of the specific colors of birds.
    (National Academy of Sciences, 2023-08-14) Delhey K; Valcu M; Muck C; Dale J; Kempenaers B; Losos J
    Animal coloration is one of the most conspicuous aspects of human-perceived organismal diversity, yet also one of the least understood. In particular, explaining why species have specific colors (e.g., blue vs. red) has proven elusive. Here, we quantify for nearly all bird species, the proportion of the body covered by each of 12 human-visible color categories, and test whether existing theory can predict the direction of color evolution. The most common colors are black, white, gray and brown, while the rarest are green, blue, purple, and red. Males have more blue, purple, red, or black, whereas females have more yellow, brown, or gray. Sexual dichromatism is partly due to sexual selection favoring ornamental colors in males but not in females. However, sexual selection also correlated positively with brown in both sexes. Strong social selection favors red and black, colors used in agonistic signaling, with the strongest effects in females. Reduced predation risk selects against cryptic colors (e.g., brown) and favors specific ornamental colors (e.g., black). Nocturnality is mainly associated with brown. The effects of habitat use support the sensory drive theory for camouflage and signaling. Darker colors are more common in species living in wet and cold climates, matching ecogeographical rules. Our study unambiguously supports existing theories of color evolution across an entire class of vertebrates, but much variation remains unexplained.
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    The evolution of carotenoid-based plumage colours in passerine birds
    (John Wiley and Sons Ltd on behalf of British Ecological Society, 2023-01-04) Delhey K; Valcu M; Dale J; Kempenaers B; Willink B
    1. Many birds use carotenoids to colour their plumage yellow to red. Because birds cannot synthesise carotenoids, they need to obtain these pigments from food, although some species metabolise dietary carotenoids (which are often yellow) into derived carotenoids (often red). 2. Here, we study the occurrence of yellow and red carotenoid-based plumage colours in the passerines, the largest bird radiation and quantify the effects of potential ecological and life-history drivers on their evolution. 3. We scored the presence/absence of yellow and red carotenoid-based plumage in nearly 6,000 species and use Bayesian phylogenetic mixed models to assess the effects of carotenoid-availability in diet, primary productivity, body size, habitat and sexual selection. We also test the widespread assumption that red carotenoid-based colours are more likely to be the result of metabolization. Finally, we analyse the pattern of evolutionary transitions between yellow and red carotenoid-based plumage colours to determine whether, as predicted, the evolution of yellow carotenoid-based colours precedes red. 4. We show that, as expected, both colours are more likely to evolve in smaller species and in species with carotenoid-rich diets. Yellow carotenoid-based plumage colours, but not red, are more prevalent in species that inhabit environments with higher primary productivity and closed vegetation. In general, females were more likely to have yellow and males more likely to have red carotenoid-based plumage colours, closely matching the effects of sexual selection. Our analyses also confirm that red carotenoid-based colours are more likely to be metabolised than yellow carotenoid-based colours. Evolutionary gains and losses of yellow and red carotenoid-based plumage colours indicate that red colours evolved more readily in species that already deposited yellow carotenoids, while the reverse was rarely the case. 5. Our study provides evidence for a general, directional evolutionary trend from yellow to red carotenoid-based colours, which are more likely to be the result of metabolization. This may render them potentially better indicators of quality, and thus favoured by sexual selection.
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    What drives our aesthetic attraction to birds?
    (Springer Nature Limited, 2023-09-27) Santangeli A; Haukka A; Morris W; Arkkila S; Delhey K; Kempenaers B; Valcu M; Dale J; Lehikoinen A; Mammola S
    In the Anthropocene, the era when the imprint of humans on nature is pervasive across the planet, it is of utmost importance to understand human relationships with other species. The aesthetics of nature, and of species, is one of the values that plays a role in shaping human-nature relationships. Birds are ubiquitous across the world. The beauty of birds exerts a powerful tug on human emotions, and bird-rich areas attract scores of eco-tourists. People naturally find some birds more beautiful or interesting than others, but we currently lack a global understanding of the specifics of what makes a species aesthetically attractive. Here, we used a global citizen-science database on bird attractiveness covering nearly all extant bird species, to show that there are specific visual features that drive our aesthetic appeal for some bird species over others. First, our aesthetic attraction is highest for smaller birds with specific, vivid colors (e.g., blue and red, and departing from brown-grey) and extreme ornaments (a long crest or tail). Second, our aesthetic attraction is highest for species with broad ranges, possibly because such species may be more familiar to us. The features that make us attracted to a particular bird strongly align with broad human visual aesthetic preferences in modern society. Unveiling the visual features underpinning our aesthetic attraction to birds is a critical step towards optimizing conservation (e.g., via conservation marketing) and education campaigns, and leverage the cultural ecosystem service potential of birds.