The Long-tailed Widowbird has the one of longest tails relative to its size of almost any bird.
By Rex Graham
Most of the other 115 species in the Weaver Family, and even female Long-tailed Widowbirds, have normal-sized tail feathers. What led to the male Long-tailed Widowbird to such extravagant lengths?
Charles Darwin told his friends that thinking about the origin exaggerated avian features, such as feathers, gave him terrific headaches.
Even today, ornithologists are split between two competing versions of evolution that explain how the male Long-tailed Widowbird got such a bizarre tail.
Exaggerated tails & traits
The tail ranks up there with those of other long-tailed male birds: the Red-tailed Tropicbird, Indian Peafowl, Ribbon-tailed Astrapia, Red-billed Streamertail and Marvelous Spatuletail hummingbirds, Resplendent Quetzal, Greater Racket-tailed Drogo, Asia Paradise-flycatcher, Long-tailed Whydah, Superb Lyrebird, Lady Amherst and Golden Pheasants, and Blue-crowned Motmots.
Most weavers have normal-sized tails, nothing like the Long-tailed Widowbird’s: 6 to 8 of the male’s 12 tail feathers are 0.5 meters (20 in) long. During the males’ slow-wingbeat display flights, they droop their tail feathers into a deep, black keel. The display can be observed by females from great distances across open grasslands in southern Africa.
Female Long-tailed Widowbirds chose
Each male establishes a territory on these grasslands and mate with several females that nest within their defended domain. “Females sometimes visit several males in rapid succession with ample opportunity for comparisons,” Swedish ornithologist Malte Andersson wrote in a 1982 paper in Nature.
In Andersson’s classic experiment, he cut the tail feathers of some males and glued them to the ends of the corresponding feathers of other males. He said females strongly preferred to nest in the territories of the artificially enhanced males. (Andersson also included a variety of controls that made his results unassailable.)
Darwin’s neglected idea
Andersson’s findings are often cited by scientists who support Darwin’s oft-neglected hypothesis that certain male ornaments are not favored by natural selection, but by female choice.
However, most ornithologists discount the notion that ill-defined, almost fickle preferences by one sex can shape the ornaments of the other. They argue that females like the Long-tailed Widowbird assign quasi-mathematical value to the “honest signal” health-and-vigor traits of males. In this scenario, the widowbird females use the length of males’ tail feathers in computer-like calculations to decide which male to mate with. This is the basis of the natural selection model of ornament evolution.
A rival group of ornithologists argue that sexual selection, as proposed by Darwin, (more broadly defined in modern times as “social selection” to encompass all facets of fertilization success) explains why animals sometimes have traits that are useless for survival.
“Special properties of sexual selection apply to other forms of social competition as well, showing the wisdom of Darwin’s setting it apart from natural selection as an explanation of many otherwise puzzling and extreme traits,” Mary Jane West-Eberhard, wrote in a 2014 paper in Neuroscience and Biobehavioral Reviews.
West-Eberhard, author of Developmental Plasticity and Evolution, and a researcher at the Smithsonian Tropical Research Institute at Ciudad Universitaria in Costa Rica, has led the revival of Darwin’s theory of sexual selection. It had fallen out of favor among the majority of ornithologists for 100 years.
“Darwin consistently classified health and vigor signals as products of natural, not sexual selection,” West-Eberhard wrote. “Signals under sexual selection and other kinds of social selection are favored because of their effects on others, not their value as indicators of quality in other contexts.”