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People like beautiful things. It’s no surprise: beauty is at the heart of highly profitable businesses, from cosmetics and art to the illegal wildlife trade, which some estimates rake in as much as $23bn (£20bn) a year.
Tigers and pandas show that aesthetic value can benefit wildlife conservation, attracting public support and funding. On the other hand, anything you’d want to keep out in the wild to view, someone else will probably want to own for the same reason.
Unsustainable trade in plants and animals can quickly deplete wild populations and put species at risk of extinction in certain areas, or even globally.
Passerines (birds in the order Passeriformes) are an interesting case study. This group contains the largest number of bird species, many of which are traded, and many of which are threatened with extinction.
For example, canaries were originally sought after as pets for the beautiful music they sing. But one need only look at their striking yellow plumage to see that color – and beauty – also play a role in the warblers’ popularity.
Recent research I conducted with colleagues from the University of Florida in the US, the Center for Synthesis and Analysis of Biodiversity in France and Massey University in New Zealand showed that the color of a warbler’s plumage predicts the likelihood that it will be traded as a pet. and its danger of extinction.
Color by numbers
How do you quantify color? We started by using data on the red, green and blue color values that make up the plumage of each species. This is a standard way of quantifying colors, which readers may be familiar with, for example, from television screens.
Each primary color red, green and blue takes on a value from a minimum of zero to a maximum of 255. And these so-called RGB values together indicate a specific color. For example, a bird with 255 red, 204 green, and 255 blue would appear pale pink.
Unfortunately, you can’t easily identify and classify colors using these RGB values, so we converted them into color categories using some simple math methods. We used 15 categories, including primary colors (red, green, blue), secondary colors (yellow, cyan, magenta), tertiary colors (orange, chartreuse green, spring green, cyan, purple, rose) and other color categories. brown, light (including white) and dark (including black).
Using a 3D graph with one axis for red, one for green, and one for blue, we plotted each species by its plumage color. This allows you to see how rare the colors of different species are, based on how far their color is from others in 3D space.
For the entire community of birds found in a given location, you can also see how many colors these species represent based on how much of the 3D space they occupy. This is what we call color diversity.
Our results showed that certain color categories, such as cyan and yellow, are more likely to occur in species that are traded than those that are not.
We believe that yellow is a common color in the illegal wildlife trade, partly because there are simply too many species that are yellow. In contrast, cyan is a color that occurs in far fewer species, but when it does appear, it seems highly likely to occur in highly traded species.
Other colors, such as brown, are less likely to occur on traded species compared to non-traded ones. Species with more unique coloring, such as pure white, are generally more likely to be traded.
What does all this mean for biodiversity? We have identified nearly 500 additional species that are not currently traded but are at risk of being traded in the future based on their color and how closely they are related to currently traded species.
Since the tropics contain the greatest variety of colors, both in terms of the color range of songbirds on display and the number of colorful species, most colors would be lost here if all currently traded species became extinct. The loss of these species would dull nature’s color palette, leading to generally duller bird communities with less colorful diversity globally.
This is only the first step in understanding the aesthetic value underlying the warbler trade. A better understanding of what motivates this trade can help identify species that could benefit from monitoring and regulating the trade.
Likewise, identifying, celebrating and conserving foci of color diversity has the best chance of preserving the aesthetic value of color as well as the overall biodiversity that the tropics can boast.
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