Editing Peafowl (section)

== Description ==
[[File:Eggs of Peafowl at Aravath Kasaragod.jpg|thumb|Peafowl eggs]] 
[[File:Baby Peacock (18131813108).jpg|thumb|Peachick]]
[[File:Peacock-JS.jpg|thumb|Head of adult peacock]]
[[File:Peahen at the zoo.jpg|thumb|A female peafowl, or peahen, walking freely around a zoo]]
[[File:Biomechanics-of-the-Peacocks-Display-How-Feather-Structure-and-Resonance-Influence-Multimodal-pone.0152759.s002.ogv|thumb|Video analysis of the mechanisms behind the display]]

The Indian peacock (''Pavo cristatus'') has iridescent blue and green plumage, mostly metal-like blue and green. In both species, females are a little smaller than males in terms of weight and wingspan, but males are significantly longer due to the "tail", also known as a "train".<ref>{{cite web |url=https://animals.sandiegozoo.org/animals/peafowl|title=Peafowl |date=2021 |website=San Diego Zoo Animals & Plants |publisher=[[San Diego Zoo]] |access-date=13 March 2021 |archive-date=5 March 2021 |archive-url=https://web.archive.org/web/20210305142514/https://animals.sandiegozoo.org/animals/peafowl |url-status=live}}</ref> The peacock train consists not of tail quill feathers but highly elongated upper tail coverts. These feathers are marked with eyespots, best seen when a peacock fans his tail. All species have a crest atop the head. The Indian peahen has a mixture of dull grey, brown, and green in her plumage. The female also displays her plumage to ward off female competition or signal danger to her young.

Male [[green peafowl]]s (''Pavo muticus'') have green and bronze or gold plumage, and black wings with a sheen of blue. Unlike Indian peafowl, the green peahen is similar to the male, but has shorter upper tail coverts, a more coppery neck, and overall less iridescence. Both males and females have spurs.<ref>{{Cite book |last=Darwin |first=Charles |author-link=Charles Darwin |year=1871 |title=The Descent of Man, and Selection in Relation to Sex |url=https://www.gutenberg.org/cache/epub/2300/pg2300-images.html |access-date=24 May 2023 |via=Gutenberg.org |language=en |archive-date=29 April 2023 |archive-url=https://web.archive.org/web/20230429085429/https://www.gutenberg.org/cache/epub/2300/pg2300-images.html |url-status=live }}</ref>{{page needed|date=March 2024}}

The [[Congo peafowl|Congo peacock]] (''Afropavo congensis'') male does not display his covert feathers, but uses his actual tail feathers during courtship displays. These feathers are much shorter than those of the Indian and green species, and the ocelli are much less pronounced. Females of the Indian and African species are dull grey and/or brown.

Chicks of both sexes in all the species are cryptically colored. They vary between yellow and tawny, usually with patches of darker brown or light tan and "dirty white" ivory.

Mature peahens have been recorded as suddenly growing typically male peacock plumage and making male calls.<ref>{{cite journal |last1=Morgan |first1=T. H. |title=Sex inversion in the peafowl |journal=Journal of Heredity |date=July 1942 |volume=33 |issue=7 |pages=247–248 |doi=10.1093/oxfordjournals.jhered.a105182 }}</ref> Research has suggested that changes in mature birds are due to a lack of estrogen from old or damaged ovaries, and that male plumage and calls are the default unless hormonally suppressed.<ref>{{cite news |last1=Inglis-Arkell |first1=Esther |title=The long-running mystery of why birds seemingly change sex |url=https://io9.gizmodo.com/the-long-running-mystery-of-why-birds-seemingly-change-493154825 |work=io9 |date=7 May 2013 |access-date=18 July 2020 |archive-date=19 July 2020 |archive-url=https://web.archive.org/web/20200719055312/https://io9.gizmodo.com/the-long-running-mystery-of-why-birds-seemingly-change-493154825 |url-status=live }}</ref>

=== Iridescence and structural coloration ===
{{further|Iridescence|Structural colouration}}

As with many birds, vibrant iridescent plumage colors are not primarily [[pigment]]s, but [[structural coloration]]. Optical [[Wave interference|interference]] of [[Bragg reflections]], from regular, periodic nanostructures of the [[barbule]]s (fiber-like components) of the feathers, produce the peacock's colors.<ref>{{Cite journal |last1=Zi |first1=Jian |last2=Yu |first2=Xindi |last3=Li |first3=Yizhou |last4=Hu |first4=Xinhua |last5=Xu |first5=Chun |last6=Wang |first6=Xingjun |last7=Liu |first7=Xiaohan |last8=Fu |first8=Rongtang |date=28 October 2003 |title=Coloration strategies in peacock feathers |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=100 |issue=22 |pages=12576–12578 |doi=10.1073/pnas.2133313100 |issn=0027-8424 |pmid=14557541|pmc=240659 |bibcode=2003PNAS..10012576Z |doi-access=free }}</ref> Slight changes to the spacing of the barbules result in different colors. Brown feathers are a mixture of red and blue: one color is created by the periodic structure and the other is created by a [[Fabry–Pérot interferometer|Fabry–Pérot interference]] peak from reflections from the outer and inner boundaries. Color derived from physical structure rather than pigment can vary with viewing angle, causing iridescence.<ref>{{cite journal |last1=Blau |first1=Steven K. |title=Light as a Feather: Structural Elements Give Peacock Plumes Their Color |journal=Physics Today |date=January 2004 |volume=57 |issue=1 |pages=18–20 |doi=10.1063/1.1650059 |bibcode=2004PhT....57a..18B |doi-access=free }}</ref>

=== Courtship ===
Most commonly, during a courtship display, the visiting peahen will stop directly in front of the peacock, thus providing her with the ability to assess the male at 90° to the surface of the feather. Then, the male will turn and display his feathers about 45° to the right of the sun's azimuth which allows the sunlight to accentuate the iridescence of his train. If the female chooses to interact with the male, he will then turn to face her and shiver his train so as to begin the mating process.<ref>{{cite journal |last1=Adeline Loyau, Doris Gomez, Benoît Moureau, Marc Théry, Nathan S. Hart, Michel Saint Jalme, Andrew T.D. Bennett, Gabriele Sorci| title=Iridescent structurally based coloration of eyespots correlates with mating success in the peacock| journal=Behavioral Ecology| date=November 2007|volume=18| issue=6| pages=1123–1131| doi=10.1093/beheco/arm088| doi-access=free}}</ref>

=== Evolution===
====Sexual selection ====
[[Charles Darwin]] suggested in ''[[The Descent of Man and Selection in Relation to Sex]]'' that peafowl plumage may have evolved through [[sexual selection]]:

{{blockquote|Many female progenitors of the peacock must, during a long line of descent, have appreciated this superiority; for they have unconsciously, by the continued preference for the most beautiful males, rendered the peacock the most splendid of living birds. }}

==== Aposematism and natural selection ====
It has been suggested that a peacock's train, loud call, and fearless behavior have been formed by natural selection (with or without sexual selection too), and served as an [[aposematic]] display to intimidate predators and rivals.<ref name="jj2">{{Cite journal |last=Jordania |first=Joseph |author-link=Joseph Jordania |date=September 2021 |title=Can there be an Alternative Evolutionary Reason Behind the Peacock's Impressive Train? |url=https://www.academia.edu/54119122 |journal=Academia Letters |doi=10.20935/AL3534 |s2cid=244187388 |access-date=8 October 2021 |archive-date=26 March 2023 |archive-url=https://web.archive.org/web/20230326030154/https://www.academia.edu/54119122 |url-status=live }}</ref><ref>{{cite book |last=Jordania |first=Joseph |year=2011 |chapter=Peacock's Tail: Tale of Beauty and Intimidation |title=[[Why do People Sing? Music in Human Evolution]] |location=Tbilisi, Georgia |publisher=Logos |pages=192–196 |isbn=978-9941-401-86-2 }}</ref> This hypothesis is designed to explain Takahashi's observations that in Japan, neither reproductive success nor physical condition correlate with the train's length, symmetry or number of eyespots.<ref name="takahashi"/>

==== Female choice ====
{{See also|Mate choice}}[[File:Peahen in front of displaying peacock.jpg|thumb|left|Peacock (seen from behind) displaying to attract peahen in foreground]]

Multiple hypotheses involving female choice have been posited. One hypothesis is that females choose mates with good genes. Males with more exaggerated secondary sexual characteristics, such as bigger, brighter peacock trains, tend to have better genes{{Example needed|date=May 2023}} in the peahen's eyes.<ref name="Age-advertisement and the evolution">{{cite journal |last1=Manning |first1=J. T. |date=September 1989 |title=Age-advertisement and the evolution of the peacock's train |journal=Journal of Evolutionary Biology |volume=2 |issue=5 |pages=379–384 |doi=10.1046/j.1420-9101.1989.2050379.x |s2cid=86740688|doi-access=free }}</ref> These better genes directly benefit her offspring, as well as her fitness and reproductive success.

Runaway selection is another hypothesis. In runaway sexual selection, linked genes in males and females code for sexually dimorphic traits in males, and preference for those traits in females.<ref>Caldwell, Roy, and Jennifer Collins. "[http://evolution.berkeley.edu/evosite/evo101/IIIE3aRunawayselec.shtml When Sexual Selection Runs Away] {{Webarchive|url=https://web.archive.org/web/20141129135558/http://evolution.berkeley.edu/evosite/evo101/IIIE3aRunawayselec.shtml |date=29 November 2014 }}." Evolution 101: Runaway Selection. N.p., n.d. 24 November 2014.</ref> The close spatial association of [[alleles]]{{Which|date=May 2023}} for [[Locus (genetics)|loci]]{{Which|date=May 2023}} involved in the train in males, and for preference for more exuberant trains in females, on the chromosome ([[linkage disequilibrium]]) causes a [[positive feedback]] loop that exaggerates both the male traits and the female preferences.

Another hypothesis is sensory bias, in which females have a preference for a trait in a non-mating context that becomes transferred to mating, such as Merle Jacobs' food-courtship<!-- Which is correct: Food courtship, food-courtship (hyphen), or food–courtship (en dash)? --> hypothesis, which suggests that peahens are attracted to peacocks for the resemblance of their eye spots to blue berries.<ref name="Jacobs">{{cite web |last1=Jacobs |first1=Merle |title=A New Look at Darwinian Sexual Selection |url=http://naturalscience.com/ns/articles/01-11/ns_mej.html |access-date=22 May 2023 |website=NaturalSCIENCE |publisher=Heron Publishing |archive-url=https://web.archive.org/web/20140908162951/http://naturalscience.com/ns/articles/01-11/ns_mej.html |archive-date=8 September 2014 |ref=Jacobs}}</ref>

Multiple causalities for the evolution of female choice are also possible.

The peacock's train and iridescent plumage are perhaps the best-known examples of traits believed to have arisen through sexual selection, though with some controversy.<ref>[http://www.thaindian.com/newsportal/world-news/male-peacocks-feathers-fail-to-impress-females-study_10031697.html Male Peacock's Feather Fails to Impress Females: Study] {{Webarchive|url=https://web.archive.org/web/20141027052428/http://www.thaindian.com/newsportal/world-news/male-peacocks-feathers-fail-to-impress-females-study_10031697.html |date=27 October 2014 }}. The Indian News. 27 March 2008.</ref> Male peafowl erect their trains to form a shimmering fan in their display for females. Marion Petrie tested whether or not these displays signalled a male's genetic quality by studying a feral population of peafowl in [[Whipsnade Wildlife Park]] in southern England. The number of [[eyespot (mimicry)|eyespot]]s in the train predicted a male's mating success. She was able to manipulate this success by cutting the eyespots off some of the males' tails:<ref>{{cite journal |last1=Petrie |first1=Marion |last2=Halliday |first2=T. |last3=Sanders |first3=C. |year=1991 |title=Peahens prefer peacocks with elaborate trains |journal=Animal Behaviour |volume=41 |pages=323–331 |doi=10.1016/S0003-3472(05)80484-1 |issue=2|s2cid=53201236 }}</ref> females lost interest in pruned males and became attracted to untrimmed ones. Males with fewer eyespots, thus having lower mating success, suffered from greater predation.<ref>{{cite journal |last=Petrie |first=M. |year=1992 |title= Peacocks with low mating success are more likely to suffer predation |journal=Animal Behaviour |doi=10.1016/0003-3472(92)90072-H |url=https://www.researchgate.net/publication/232545934 |volume=44 |pages=585–586|s2cid=53167596 }}</ref> She allowed females to mate with males with differing numbers of eyespots, and reared the offspring in a communal incubator to control for differences in maternal care. Chicks fathered by more ornamented males weighed more than those fathered by less ornamented males, an attribute generally associated with better survival rate in birds. These chicks were released into the park and recaptured one year later. Those with heavily ornamented feathers were better able to avoid predators and survive in natural conditions.<ref name="Zuk">Zuk, Marlene. (2002). ''Sexual Selections: What we can and can't learn about sex from animals''. University of California Press; Berkeley, CA. {{ISBN|0520240758}}</ref> Thus, Petrie's work shows correlations between tail ornamentation, mating success, and increased survival ability in both the ornamented males and their offspring.

[[File:Peacock Flying.jpg|thumb|A peacock in flight: Zahavi argued that the long train would be a handicap.]]

Furthermore, peafowl and their sexual characteristics have been used in the discussion of the causes for sexual traits. Amotz Zahavi used the excessive tail plumes of male peafowls as evidence for his "[[handicap principle]]".<ref>{{cite journal|last1=Zahavi|first1=Amotz|title=Mate selection—A selection for a handicap|journal=Journal of Theoretical Biology|volume=53|issue=1|year=1975|pages=205–214|pmid=1195756|doi=10.1016/0022-5193(75)90111-3|bibcode=1975JThBi..53..205Z|url=http://ckwri.tamuk.edu/fileadmin/tpl/misc/Selection_for_a_handicap_Zahavi_1975.pdf|citeseerx=10.1.1.586.3819|access-date=28 August 2015|archive-url=https://web.archive.org/web/20160126204931/http://ckwri.tamuk.edu/fileadmin/tpl/misc/Selection_for_a_handicap_Zahavi_1975.pdf|archive-date=26 January 2016|url-status=dead}}</ref> Since these trains are likely to be deleterious to an individual's survival (as their brilliance makes them more visible to [[predator]]s and their length hinders escape from danger), Zahavi argued that only the fittest males could survive the handicap of a large train. Thus, a brilliant train serves as an [[signalling theory|honest indicator]] for females that these highly ornamented males are good at surviving for other reasons, so are preferable mates.<ref>{{cite journal |last1=Loyau |first1=Adeline |last2=Saint Jalme |first2=Michel |last3=Cagniant |first3=Cécile |last4=Sorci |first4=Gabriele |title=Multiple sexual advertisements honestly reflect health status in peacocks (''Pavo cristatus'') |journal=Behavioral Ecology and Sociobiology |date=October 2005 |volume=58 |issue=6 |pages=552–557 |doi=10.1007/s00265-005-0958-y |s2cid=27621492 }}</ref> This theory may be contrasted with [[Ronald Fisher]]'s hypothesis that male sexual traits are the result of initially arbitrary [[aesthetic]] selection by females.

In contrast to Petrie's findings, a seven-year Japanese study of free-ranging peafowl concluded that female peafowl do not select mates solely on the basis of their trains. Mariko Takahashi found no evidence that peahens preferred peacocks with more elaborate trains (such as with more eyespots), a more symmetrical arrangement, or a greater length.<ref name="takahashi">{{cite journal |last1=Takahashi |first1=Mariko |last2=Arita |first2=Hiroyuki |last3=Hiraiwa-Hasegawa |first3=Mariko |last4=Hasegawa |first4=Toshikazu |title=Peahens do not prefer peacocks with more elaborate trains |journal=Animal Behaviour |date=April 2008 |volume=75 |issue=4 |pages=1209–1219 |doi=10.1016/j.anbehav.2007.10.004 |s2cid=53196851 |url=http://id.nii.ac.jp/1013/00003652/ }}</ref> Takahashi determined that the peacock's train was not the universal target of female [[mate choice]], showed little variance across male populations, and did not correlate with male physiological condition. Adeline Loyau and her colleagues responded that alternative and possibly central explanations for these results had been overlooked.<ref>{{cite journal |last1=Loyau |first1=Adeline |last2=Petrie |first2=Marion |last3=Saint Jalme |first3=Michel |last4=Sorci |first4=Gabriele |title=Do peahens not prefer peacocks with more elaborate trains? |journal=Animal Behaviour |date=November 2008 |volume=76 |issue=5 |pages=e5–e9 |doi=10.1016/j.anbehav.2008.07.021 |s2cid=40638610 }}</ref> They concluded that female choice might indeed vary in different ecological conditions.

==== Plumage colours as attractants ====
[[File:Peacock Feather Close Up.JPG|thumb|upright|Eyespot on a peacock's train feather]]

A peacock's copulation success rate depends on the colours of his [[eyespot (mimicry)|eyespots (ocelli)]] and the angle at which they are displayed. The angle at which the ocelli are displayed during courtship is more important in a peahen's choice of males than train size or number of ocelli.<ref name=Dakin>{{cite journal |last1=Dakin |first1=Roslyn |last2=Montgomerie |first2=Robert |date=June 2013 |title=Eye for an eyespot: how iridescent plumage ocelli influence peacock mating success |journal=Behavioral Ecology |volume=24 |issue=5 |pages=1048–1057 |doi=10.1093/beheco/art045 |doi-access=free }}</ref> Peahens pay careful attention to the different parts of a peacock's train during his display. The lower train is usually evaluated during close-up courtship, while the upper train is more of a long-distance attraction signal. Actions such as train rattling and wing shaking also kept the peahens' attention.<ref>{{cite journal |last1=Yorzinski |first1=Jessica L. |last2=Patricelli |first2=Gail L. |last3=Babcock |first3=Jason S. |last4=Pearson |first4=John M. |last5=Platt |first5=Michael L. |title=Through their eyes: selective attention in peahens during courtship |journal=The Journal of Experimental Biology |date=15 August 2013 |volume=216 |issue=16 |pages=3035–3046 |doi=10.1242/jeb.087338 |pmid=23885088 |pmc=4232502 |bibcode=2013JExpB.216.3035Y }}</ref>

==== Redundant signal hypothesis ====
Although an intricate display catches a peahen's attention, the redundant signal hypothesis also plays a crucial role in keeping this attention on the peacock's display. The redundant signal hypothesis explains that whilst each signal that a male projects is about the same quality, the addition of multiple signals enhances the reliability of that mate. This idea also suggests that the success of multiple signalling is not only due to the repetitiveness of the signal, but also of multiple receivers of the signal. In the peacock species, males congregate a communal display during breeding season and the peahens observe. Peacocks first defend their territory through intra-sexual behaviour, defending their areas from intruders. They fight for areas within the congregation to display a strong front for the peahens. Central positions are usually taken by older, dominant males, which influences mating success. Certain morphological and behavioural traits come in to play during inter and intra-sexual selection, which include train length for territory acquisition and visual and vocal displays involved in mate choice by peahens.<ref>{{cite journal |last1=Loyau |first1=Adeline |last2=Jalme |first2=Michel Saint |last3=Sorci |first3=Gabriele |title=Intra- and Intersexual Selection for Multiple Traits in the Peacock (''Pavo cristatus'') |journal=Ethology |date=September 2005 |volume=111 |issue=9 |pages=810–820 |doi=10.1111/j.1439-0310.2005.01091.x |bibcode=2005Ethol.111..810L }}</ref>