Cornell Bird Lab produced a series of quite informative teaching materials to provide scientific explanation for how new species have evolved (and are evolving). Evolution is not only a struggle for existence, it is also an effort to pass on genes to next generation. Modern biology has described mechanisms of evolution with fine details and this video effectively tells how natural selection works with three cartoonified traits in an island setting at the first few minutes.
In many animals females are less showy and tend to have camouflaging coloration. Alfred Russel Wallace, another influential biologist contemporary to Charles Darwin who also independently came up with the idea of natural selection argued that dull coloration could arise because females face different risks than males, being burdened with motherhood. In his 1867 essay titled “Theory of Birds’ Nest” Wallace elaborated why being less noticeable can be an adaptive trait.
Behavior is one of the major selective forces in formation of new species. Sexual selection is a specialized form of natural selection and can operate under certain environmental determinants. For instance, resource distribution can drive evolution of different behavior types. If resources are clumped most males will develop exaggerated armaments to defend their territories and capitalize on females. If resources are spread evenly to large areas armaments can become ornaments (bright colors, elaborate singing and cool flashy dance moves) to attract and impress females. Sexy son hypothesis is one of proposed genetic explanation for this kind of male evolution based on female mate choice first coined by influential evolutionary biologist Ronald Fisher in 1930. Females are the choosy sex however the opposite can be observed in sex-role reversed species where males can be the choosy one. Female choosiness can have many different filters in evaluation of male qualities including vision, sound and touch:
Birds are excellent study systems for understanding evolution. If you are into more bird related studies you can check out the Junco Project. This article is a part of the Evolution series aiming to categorize posts related to this central biological concept in Nature Documentaries. Additionally, you can watch an Attenborough documentary on birds of paradise. Especially, the last bit of the documentary makes a nice timeline of many attempts by prominent wildlife filmmakers to record these elusive birds and makes us appreciate more about modern high definition cameras.