page_title: Biological ornament
section_title: Use in courtship displays
hierarchical_section_title: Biological ornament / Use in courtship displays
context_page_description: A biological ornament is a characteristic of an animal that appears to serve a decorative function rather than a utilitarian function. Many are secondary sexual characteristics, and others appear on young birds during the period when they are dependent on being fed by their parents. Ornaments are used in displays to attract mates, which may lead to the evolutionary process known as sexual selection. An animal may shake, lengthen, or spread out its ornament in order to get the attention of the opposite sex, which will in turn choose the most attractive one with which to mate. Ornaments are most often observed in males and choosing an extravagantly ornamented male benefits females because the genes that produce the ornament will be passed on to her offspring, increasing their own reproductive fitness. As Ronald Fisher noted, the male offspring will inherit the ornament while the female offspring will inherit the preference for said ornament, which can lead to a positive feedback loop known as a Fisherian runaway. These structures serve as cues to animal sexual behaviour, that is, they are sensory signals that affect mating responses.
context_section_description: Biological ornaments are used in courtship displays in many species, especially insects, fish, and birds. A well known ornament used in courting displays is seen in peafowls. Male peacocks spread and shake their tails to attract and impress potential mates. Peahens choose the peacocks with the largest number of eyespots on their tails, because only the healthiest peacocks can afford to divert energy and nutrients towards growing expensive and cumbersome plumage, as explained by the handicap principle. More elaborate ornamentation increases the likelihood that a male will mate and has been shown to affect survival of their offspring. The offspring of males with larger eyespots on their ornamented tails have been shown to weigh more and were more likely to be alive after 2 years than the progeny of males with fewer eyespots.
  Ornaments that play a role in reproduction develop under the influence of two series of genes. First, it develops from genes in males that determine the presence and characteristics of the ornament, and second it develops from genes in females that draw her to this kind of ornamentation. Important studies concerning this have been conducted in the Stalk-eyed fly, showing that females are attracted to mates that share characteristics with their fathers. Therefore, sexual selection is a mechanism that differently affects both sexes. Initially, an ornament may have been selected for reasons not linked to reproduction, but over time, the characteristic may become exaggerated due to sexual selection.  The females will select for more and more elaborate ornamentation, which represents better survival skills because the male with those characteristics must be physically fit enough to handle the unwanted predator attention that comes with the ornament.  Therefore, the males with the most extreme ornamentation will have more offspring, and the gene for "showiness" will be passed on. This evolution can then lead to organs of excessive size that may become troublesome for the males, such as large, bushy tails, bright feathers, etc.  The point of equilibrium is reached when their ornamentation becomes too much of a handicap on the male's survival, and the "vital" natural selection goes to work, altering the exaggerated characteristic until it reaches an equilibrium point.
  Sexually selected ornaments of males may impose survival costs but advance success in the competition for mates. The interesting thing about sexual ornaments is that they impede the male's chances for survival, yet they continue to be passed on from generation to generation.  The larger the male peacock's tail feathers are, or the brighter the birds feathers are, the harder it is for them to escape predators and maneuver through trees, and the more food they will need to eat to develop the ornament.  A peacock's tail almost certainly reduces survival of the peacock as they reduce
  maneuverability, power of flight, and make the bird more conspicuous to predators. Ornaments, therefore, have a great effect on the fitness of the animals that carry them, but the benefits of having an ornament must outweigh the costs for them to be passed on.
caption: A male peacock courting a female peahen with his large tail
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