Wednesday, June 24, 2015
The Language of Feathers
In the bird world, special coloration of feathers and quality of feathers plays a great role in the choice of mates for breeding purposes. Ornithologists call this process “sexual signaling”.
An English Budgie and a Common Parakeet (photo: Dawn Griffard)
The female bird will make a careful selection of a potential mate by examining the quality of his feathers along with the brightness, iridescence and saturation of their hues. Female birds are so judgmental because they instinctively want to choose the healthiest male to mate with in order to ensure the continuation of their species.
High quality feathers require a lot of energy and strength to create and maintain. Weak and sickly males cannot afford such flashy feathers, as they must use every ounce of their energy for mere survival. Therefore, that showy male is the best choice with which to create strong, healthy babies. However, the cost of such flamboyance is high. Bright colors and an often long, heavy tail mean that the male is more conspicuous to predators and may have a harder time escaping through flight due to the added weight.
Because of the high cost of these bright colors, some species’ spring molt creates what is called an “alternate plumage”, which allows them to have brighter feathers for just the breeding season. This can be seen in the bright spring colors of buntings, grosbeaks and wood-warblers. This spring molt may be just a partial molt which replaces feathers in only certain areas. This requires much less energy than a complete molt.
While we humans can see many of those gorgeous feather colors that birds can display, some birds can see so much more. Humans can see only a portion of the electromagnetic spectrum. The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation. The “visible spectrum” is the portion of the electromagnetic spectrum that is visible to the human eye. Birds can see the same visible spectrum that we can, but they can also additionally see the ultraviolet spectrum. The ultraviolet spectrum is invisible to the human eye. The fact that the ultraviolet light can be seen by birds opens up a whole other world of possible “sexual signaling” coloration.
A photo sowing the fluorescent feathers of a parakeet under a blacklight (photo: Dawn Griffard)
Just like those colors that can be seen in the visible spectrum, colors that can be seen only in the ultraviolet (UV) spectrum can be difficult for the birds to create and maintain. Therefore, they are also proof of the strength and excellent health of the bird that displays them with gusto.
Recent studies have found that it is mainly parrot species that display these ultraviolet colorations. Most species of parrot are not sexually dimorphic, which means that males and females have similarly colored feathers. For example, the northern cardinal is clearly sexually dimorphic – the male bird is bright red, while the female is dull brown/gray with somewhat red wings and tail. Most parrot species do not have these noticeable differences in coloration. Perhaps this is why they have the added ability to create the different colors in the UV spectrum in addition to the visible spectrum – to prove their virility.
A male and female Blue Front Amazon Parrot (photo: Dawn Griffard)
In addition to the UV reflective plumage, many of these parrots also have “fluorescing” plumage. Fluorescent and UV reflective plumage on parrots are often found adjacent to each other and are most often found in body regions associated with active courtship displays. Although it has not yet been proven, it follows that this coloration is probably also used in sexual signaling for breeding purposes.
Coloration and feather quality is not always the way that males (and sometimes females) prove their worth. Sometimes it also involves an elaborate song or a complicated dance. But a beautiful song or dance without a fitting costume is a pale performance.
Submitted by Dawn Trainor Griffard, World Bird Sanctuary Naturalist