page_title: Sexual selection in birds
section_title: Visual signaling
hierarchical_section_title: Sexual selection in birds / Visual signaling
caption_attribution_description: Deutsch: Rothuhn. Eesti: Lääne-kivikana. English: Red-legged Partridge. Français: Perdrix rouge.
context_page_description: Sexual selection in birds concerns how birds have evolved a variety of mating behaviors, with the peacock tail being perhaps the most famous example of sexual selection and the Fisherian runaway. Commonly occurring sexual dimorphisms such as size and color differences are energetically costly attributes that signal competitive breeding situations. Many types of avian sexual selection have been identified; intersexual selection, also known as female choice; and intrasexual competition, where individuals of the more abundant sex compete with each other for the privilege to mate. Sexually selected traits often evolve to become more pronounced in competitive breeding situations until the trait begins to limit the individual's fitness. Conflicts between an individual fitness and signaling adaptations ensure that sexually selected ornaments such as plumage coloration and courtship behavior are “honest” traits. Signals must be costly to ensure that only good-quality individuals can present these exaggerated sexual ornaments and behaviors.
context_section_description: Birds also use visual stimuli such as bright colors or large ornamentation for socio-sexual communication as well as species recognition.  These ornaments can be considered “honest” signs of fitness because they are often costly to produce and show that the individual is healthy enough to mate with the choosing female.
  The peacock's plumage shows intersexual selection, where ornate males compete to be chosen by females. The result is a stunning feathered display, which is large and unwieldy enough to pose a significant survival disadvantage, demonstrating the handicap principle, and possibly provide a means of demonstrating body symmetry, such that peahens are "trying" to discover the health of the male or the fitness of his genes. Diseases, injuries, and genetic disorders may impair the body's symmetry and the tail.
  In experiments where eyespots are removed from their tail feathers, also known as trains, there is a significant decline in mating success compared with a control group. This supports the hypothesis that the train elaboration evolved, at least in part, as a result of female choice. The most common explanation for this adaptation is that the females gain indirect benefits such as good genes for their offspring. Peafowl are lekking species and males provide no care to their offspring, therefore females do not gain any direct benefits from mating with a more elaborate male.  However, conflicting evidence has been found that removal of a large number of eyespots (≤20) from a male's train does reduce his mating success, although this is outside the natural variation of eyespot loss. This shows that peafowl preference is more complex than originally thought.  Takahashi et al., 2008, found no evidence that peahens expressed any preference for males with more elaborate trains. This shows that trains are not the universal target for female choice due to their small variance among males across populations. A peacock's train is also not a reliable indicator of the individual's condition. Although the train may be necessary for mating success, the females seem to be more affected by the males' behavioral characteristics during courtship.
  In great bustards, age, weight, and display effort are all significant and independent predictors of male mating success, where whiskers and neck plumage are reliable indicators of male age and weight. A male's sexual display consists of a series of extravagant body postures and movements that end, when an interested female approaches, with a reiterative and almost obstinate exhibition of the cloaca, which is fully surrounded by pure white feathers that allow an easy detection of possible parasites or their remains. Exposure of the cloaca is widespread in pre-copulatory displays of birds and has been related with high probability of transmission of sexual diseases. Male great bustards may use the highly toxic cantharidin taken from blister beetles of the genus Meloe to clean their intestine and cloaca plumage from parasites. Cantharidin can kill a great bustard if many beetles are ingested. Self-medication could have evolved in great bustards as a sexual selection mechanism capable of transmitting to females a signal of good resistance to a poisonous compound, in a similar way as other costly secondary sexual traits are exhibited by males of many species.  Great bustards may eat toxic blister beetles of the genus Meloe to increase the sexual arousal of males.
  In parrots, ornate males with brighter plumage are preferred by the females. These males are typically immunologically superior with higher leukocyte counts. This evidence supports the idea that bright plumage is an “honest” signal involved in mating. The female California quail uses multiple male plumage characteristics when deciding on a mate and responds in different ways to a variety of artificially manipulated traits. Various visual signals act in combination to attract a mate and female choice will shift toward several particularly exaggerated traits.  In the red-legged partridge, male carotenoid ornamentation is positively c
caption: Red-legged partridge
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