Wednesday, 21 September 2011

Sexy feathers from grass

A guest blog post by Dr Mark Brown (University of KwaZulu-Natal-Pietermaritzburg)

So here I am, an avid ornithologist asked to write about grass... wow, really? Is grass actually useful? Just kidding Craig! Well as the title suggests, grass is quite useful for some birds apart from just being a source of food (seed). For some species, it's what they get out of grass that turns the ladies’ eye...

Male Red Bishop

The colors in the feathers of a bird are formed in two different ways, from either pigments or from light refraction caused by the structure of the feather. In some cases feather colors are the result of a combination of pigment and structural colors. The greens of some parrots are the result of yellow pigments overlaying the blue-reflecting characteristic of the feathers.
Pigments are colored substances that can be found in both plants and animals. The coloration created by pigments is independent of the structure of the feather. Pigment colorization in birds comes from three different groups: melanins, carotenoids, and porphyrines. This is where the grass comes in... Carotenoids are found in low quantities in grass seeds, which many granivorous birds eat.
In South Africa it is the genus Euplectes, the bishops and widowbirds, that are the main users of these pigments. The beneficial effects of high levels of carotenoids are well documented by scientists: as antioxidants they are thought to improve bird’s health, and the resulting bright feathers signal to female birds that males are healthy, have less parasites and a good diet.
Male Red Bishop pimping up his feathers
What? Grass makes birds sexy? Yup! Several good local studies have showed that there are two sexual selection systems in the Euplectes: long tails are important, and bright colors are important. In terms of long tails; yes ladies, sometimes size DOES count, as long as it is symmetrical! Female red-collared and long-tailed widowbirds prefer males with long, symmetrical tails.
Color is important two, but operates differently in different species. In red bishops, brighter (plumage not IQ) males attract more females to their harem and have higher reproductive success (more fun...). In red-collared and fan-tailed widowbirds, however, the colorful badges have an additional role... In these species, Sarah Pryke, Staffan Andersson and colleagues have shown that colorful badges also signal quality and dominance to other males... Basically, the pecking order is reflected by the badges... By manipulating the badge size and color, they showed that the pecking order changed to reflect the new badge order. End point is that the redder the badge, the higher up the pecking order you are with other males...
Color signals in birds are so called "honest signals". Producing the bright colors is costly, only those males in good condition with access to good food resources can collect enough carotenoids and put enough energy into plumage development to produce the brightest signals. In addition, it's not just the ladies that bright colors attract either! Predators would find it easy to pick off weak but colorful males, were they able to scrape such a plumage together... So in essence, male and female Euplects birds can easily assess the quality of other males and females very effectively - there is no cheating involved - unlike for us where we can steal a Ferrari, wear fake raybans, don a Magnum PI shirt, pump pirated music out the windows and have the ladies think we might be a good catch...
So next time you see a tired looking brightly colored male red bishop at your feeder or in the grassland, give him some respect - it's hard work looking so good!

Male Fan-tailed Widowbird (formely Red-shouldered Widow)