Analysis: many of the birds who dress to impress a potential mate also have longer lifespans and higher adult survival rates
There are two types of animal species on our planet; those where males and females are essentially identical in appearance and those that are not. Think of male deer that sport large antlers or male lions that grow magnificent manes. We refer to such species where there is a dissimilarity between the sexes as sexual dimorphism, where these physical traits typically help males to impress a potential mate.
Animals do a lot to try and attract a mate. Some sing, some dance and some fight, while others "dress to impress" through bold and vibrant colours. The type of sexual dimorphism associated with those that dress to impress is called sexual dichromatism and is widespread in many familiar species of butterflies, fish, amphibian, reptiles and birds.
One of the most well-known examples is the extravagantly dressed male peacocks. Their vivid blues and greens and ornamental flashy tail are ostentatious compared to drab female peahens, whose attire is much more practically suited for camouflage.
From National Geographic Wild, how male peacocks try to impress females by strutting their stuff
But you don't have to look further than your back garden to see sexual dichromatism for yourself. The pure black plumage and bright orange beaks of male blackbirds contrast with the mottled brown of females. Male Mallard ducks glint in blues and greens, while male pheasants parade reds and oranges to less visible potential mates.
There are also less obvious examples of sexual dichromatism. Male and female Great Tit birds can only be distinguished by the thickness of the black band on their stomach area, with males having thicker bands. Others, like the robin and wren, are barely distinguishable at all.
So why are some species more dichromatic than others? Dichromatic species evolve due to female preference and male competition with other eligible bachelors. In species where females favour brightly coloured males, females must choose from a range of candidates and pick the one she deems the best one to mate with. In bird species which mate in group settings, the stakes are higher than in solitary breeding species because the females will have more males to choose from, so the stakes are raised, and competition is fierce.
From National Geographic Wild, Greater Sage Grouses display their unique mating ritual.
Lekking is a behaviour where many males of a species gather in an area and compete for mating rights through visual displays, allowing females to choose a male that has caught their attention. To stand out in these kinds of settings, just having a good dance routine won’t cut it, but sporting bold feathers might increase your odds. Lekking behaviour can be seen in many land fowl species, such as the native Red Grouse and Greater-sage Grouse in North America.
In contrast some species show little or no dichromatism if it's not the right tool to attract a mate. For instance, nocturnal bird species, such as barn owls, are rarely dichromatic as they cannot rely on visual signals, instead relying more on vocal displays to attract a mate. After all, looks aren’t everything.
For those males that do employ bright feathers to attract a suitor, it can come at a cost. Reds, blues and blacks require energetically expensive pigments and using bold colours is a bold strategy when predators are searching for their next meal. However, such costs may actually be the point of these colours.
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From RTÉ Radio 1's Mooney Goes Wild, Dr. Andrew Parnell from the University of Sheffield on why the colour of bird feathers never fades
Our ongoing research has found that bird species with higher levels of sexual dichromatism have longer lifespans and have higher adult survival rates than species with lower levels of dichromatism. Instead of being a hindrance to their survival, higher levels of dichromatism is actually an honest signal of fitness in birds, meaning what you see is what you get. If a male is able to pull off such bold and bright colours, it means that he is fit enough to carry them, and that they have not impacted his odds of survival in a negative way.
Birds are one of the few animal groups where sexual dichromatism is very prevalent, and it probably has something to do with their morphology. Birds are able to fly, something rarely seen in other vertebrate groups (except for bats and extinct pterosaurs). Compared to other terrestrial animals, they are able to make a quicker escape from predators by taking to the air. Colourful plumage, especially in males, does not put birds in considerably more danger of predation, meaning male plumage could become brighter and bolder to appeal to the females. You know what they say: if you've got it flaunt it!
The views expressed here are those of the author and do not represent or reflect the views of RTÉ
