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Various non-human animal species exhibit behavior that can be interpreted as homosexual or
bisexual Bisexuality is a romantic or sexual attraction or behavior toward both males and females, or to more than one gender. It may also be defined to include romantic or sexual attraction to people regardless of their sex or gender identity, whic ...
. This may include same-sex sexual activity,
courtship Courtship is the period wherein some couples get to know each other prior to a possible marriage. Courtship traditionally may begin after a betrothal and may conclude with the celebration of marriage. A courtship may be an informal and private m ...
,
affection Affection or fondness is a "disposition or state of mind or body" that is often associated with a feeling or type of love. It has given rise to a number of branches of philosophy and psychology concerning emotion, disease, influence, and sta ...
,
pair bond In biology, a pair bond is the strong affinity that develops in some species between a mating pair, often leading to the production and rearing of offspring and potentially a lifelong bond. Pair-bonding is a term coined in the 1940s that is freque ...
ing, and parenting among same-sex animal pairs.Braithwaite, L. W., "Ecological studies of the Black Swan III – Behaviour and social organization", ''Australian Wildlife Research'' 8, 1981: 134–146 * Various forms of this are found in every major geographic region and every major animal group. The sexual behavior of non-human animals takes many different forms, even within the same species, though homosexual behavior is best known from social species. Scientists perceive homosexual behavior in
animals Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and go through an ontogenetic stage in ...
to different degrees. According to Bruce Bagemihl, same-sex behavior (comprising courtship, sexual, pair-bonding, and parental activities) has been documented in over 450 species of animals worldwide. Although same-sex interactions involving genital contact have been reported in hundreds of animal species, they are routinely manifested in only a few, including humans.
Simon LeVay Simon LeVay (born 28 August 1943 in Oxford, England) is a British-American neuroscientist. He received a bachelor's degree in natural sciences from the University of Cambridge in 1966, a Ph.D. in Neuroanatomy at the University of Göttingen ...
stated that " though homosexual behavior is very common in the animal world, it seems to be very uncommon that individual animals have a long-lasting predisposition to engage in such behavior to the exclusion of heterosexual activities. Thus, a homosexual orientation, if one can speak of such thing in animals, seems to be a rarity." The motivations for and implications of these behaviors are lensed through anthropocentric thinking; Bagemihl notes that any hypothesis is "necessarily an account of human interpretations of these phenomena". One species in which exclusive homosexual orientation occurs is the domesticated sheep ('' Ovis aries''). "About 10% of rams (males), refuse to mate with ewes (females) but do readily mate with other rams."


In relation to humans


Applying the term ''homosexual'' to animals

The term ''homosexual'' was coined by the Hungarian writer and campaigner Karl Maria Kertbeny in 1868 to describe same-sex sexual attraction and sexual behavior in humans. Its use in animal studies has been controversial for two main reasons: animal sexuality and motivating factors have been and remain poorly understood, and the term has strong cultural implications in western society that are irrelevant for species other than humans. Thus homosexual behavior has been given a number of terms over the years. According to Bruce Bagemihl, when describing animals, the term ''homosexual'' is preferred over ''gay'', ''lesbian'', and other terms currently in use, as these are seen as even more bound to human homosexuality.Bagemihl 1999, pp. 122–166. Bailey et al. says:
Homosexual: in animals, this has been used to refer to same-sex behavior that is not sexual in character (e.g. 'homosexual tandem running' in termites), same-sex courtship or copulatory behavior occurring over a short period of time (e.g. 'homosexual mounting' in cockroaches and rams) or long-term pair bonds between same-sex partners that might involve any combination of courting, copulating, parenting and affectional behaviors (e.g. 'homosexual pair bonds' in gulls). In humans, the term is used to describe individual sexual behaviors as well as long-term relationships, but in some usages connotes a gay or lesbian social identity. Scientific writing would benefit from reserving this anthropomorphic term for humans and not using it to describe behavior in other animals, because of its deeply rooted context in human society.
Animal preference and motivation is always inferred from behavior. In wild animals, researchers will as a rule not be able to map the entire life of an individual, and must infer from frequency of single observations of behavior. The correct usage of the term ''homosexual'' is that an animal ''exhibits homosexual behavior'' or even ''same-sex sexual behavior''; however, this article conforms to the usage by modern research, applying the term ''homosexuality'' to all sexual behavior (
copulation Sexual intercourse (or coitus or copulation) is a sexual activity typically involving the insertion and thrusting of the penis into the vagina for sexual pleasure or reproduction.Sexual intercourse most commonly means penile–vaginal penetra ...
, genital stimulation, mating games and sexual
display behavior Display behaviour is a set of ritualized behaviours that enable an animal to communicate to other animals (typically of the same species) about specific stimuli. These ritualized behaviours can be visual however many animals depend on a mixture ...
) between animals of the same sex. In most instances, it is presumed that the homosexual behavior is but part of the animal's overall sexual behavioral repertoire, making the animal "bisexual" rather than "homosexual" as the terms are commonly understood in humans.


Nature

The observation of homosexual behavior in animals can be seen as both an argument for and against the acceptance of homosexuality in humans, and has been used especially against the claim that it is a '' peccatum contra naturam'' ("sin against nature"). For instance, homosexuality in animals was cited by the
American Psychiatric Association The American Psychiatric Association (APA) is the main professional organization of psychiatrists and trainee psychiatrists in the United States, and the largest psychiatric organization in the world. It has more than 37,000 members are invo ...
and other groups in their '' amici curiae'' brief to the
United States Supreme Court The Supreme Court of the United States (SCOTUS) is the highest court in the federal judiciary of the United States. It has ultimate appellate jurisdiction over all U.S. federal court cases, and over state court cases that involve a point o ...
in ''
Lawrence v. Texas ''Lawrence v. Texas'', 539 U.S. 558 (2003), is a landmark decision of the U.S. Supreme Court in which the Court ruled that most sanctions of criminal punishment for consensual, adult non- procreative sexual activity (commonly referred to as sod ...
'', which ultimately struck down the sodomy laws of 14 states.


Research

A majority of the research available concerning homosexual behavior in animals lacks specification between animals that exclusively exhibit same-sex tendencies and those that participate in heterosexual and homosexual mating activities interchangeably. This lack of distinction has led to differing opinions and conflicting interpretations of collected data amongst scientists and researchers. For instance, Bruce Bagemihl, author of the book ''Biological Exuberence: Animal Homosexuality and Natural Diversity'', emphasizes that there are no anatomical or endocrinological differences between exclusively homosexual and exclusively heterosexual animal pairs. However, if the definition of "homosexual behavior" is made to include animals that participate in both same-sex and opposite-sex mating activities, hormonal differences have been documented among key sex hormones, such as
testosterone Testosterone is the primary sex hormone and anabolic steroid in males. In humans, testosterone plays a key role in the development of male reproductive tissues such as testes and prostate, as well as promoting secondary sexual characteristi ...
and
estradiol Estradiol (E2), also spelled oestradiol, is an estrogen steroid hormone and the major female sex hormone. It is involved in the regulation of the estrous and menstrual female reproductive cycles. Estradiol is responsible for the development o ...
, when compared to those who participate solely in heterosexual mating. Many of the animals used in laboratory-based studies of homosexuality do not appear to spontaneously exhibit these tendencies often in the wild. Such behavior is often elicited and exaggerated by the researcher during experimentation through the destruction of a portion of brain tissue, or by exposing the animal to high levels of steroid hormones prenatally. Information gathered from these studies is limited when applied to spontaneously occurring same-sex behavior in animals outside of the laboratory. Homosexual behaviour in animals has been discussed since
classical antiquity Classical antiquity (also the classical era, classical period or classical age) is the period of cultural history between the 8th century BC and the 5th century AD centred on the Mediterranean Sea, comprising the interlocking civilizations of ...
. The earliest written mention of animal homosexuality appears to date back to 2,300 years ago, when
Aristotle Aristotle (; grc-gre, Ἀριστοτέλης ''Aristotélēs'', ; 384–322 BC) was a Greek philosopher and polymath during the Classical period in Ancient Greece. Taught by Plato, he was the founder of the Peripatetic school of ...
(384–322 BC) described copulation between pigeons, partridges and quails of the same sex. The Hieroglyphics of Horapollo, written in the 4th century AD by the Egyptian writer Horapollo, mentions "hermaphroditism" in hyenas and homosexuality in partridges. The first review of animal homosexuality was written by the zoologist Ferdinand Karsch-Haack in 1900. Academic research into the ubiquity of same-sex sexual behavior was not carried out on a large scale, possibly due to
observer bias Observer bias is one of the types of detection bias and is defined as any kind of systematic divergence from accurate facts during observation and the recording of data and information in studies. The definition can be further expanded upon to inclu ...
caused by social attitudes to same-sex sexual behavior, innocent confusion, lack of interest, distaste, scientists fearing loss of their
grants Grant or Grants may refer to: Places *Grant County (disambiguation) Australia * Grant, Queensland, a locality in the Barcaldine Region, Queensland, Australia United Kingdom *Castle Grant United States * Grant, Alabama * Grant, Inyo County, ...
or even from a fear of "being ridiculed by their colleagues". Georgetown University
biologist A biologist is a scientist who conducts research in biology. Biologists are interested in studying life on Earth, whether it is an individual cell, a multicellular organism, or a community of interacting populations. They usually specialize ...
Janet Mann states "Scientists who study the topic are often accused of trying to forward an agenda, and their work can come under greater scrutiny than that of their colleagues who study other topics." They also noted "Not every sexual act has a reproductive function ... that's true of humans and non-humans." Studies have demonstrated homosexual behavior in a number of species, but the true extent of homosexuality in animals is not known. Some researchers believe this behavior to have its origin in male social organization and social dominance, similar to the dominance traits shown in
prison sexuality Prison sexuality (or prison sex or penitentiary sex) consists of sexual relationships between prisoners or between a prisoner and a prison employee or other persons to whom prisoners have access. Since prisons are usually separated by sex, most ...
. Others, particularly Bagemihl,
Joan Roughgarden Joan Roughgarden (born Jonathan David Roughgarden, 13 March 1946) is an American ecologist and evolutionary biologist. She has engaged in theory and observation of coevolution and competition in '' Anolis'' lizards of the Caribbean, and recruitm ...
,
Thierry Lodé Thierry Lodé (born 1956 in Tarbes) is a French biologist and professor of evolutionary ecology in a CNRS lab at the University of Rennes 1. His work deals mainly with sexual conflict.Göran Arnqvist and Locke Rowe, Eds., "Sexual conflict", Prin ...
and Paul Vasey suggest the social function of sex (both homosexual and heterosexual) is not necessarily connected to dominance, but serves to strengthen alliances and social ties within a flock. While reports on many such mating scenarios are still only anecdotal, a growing body of scientific work confirms that permanent homosexuality occurs not only in species with permanent pair bonds, but also in non-monogamous species like sheep. One report on sheep found that 8% of rams exhibited homosexual preferences—that is, even when given a choice, they chose male over female partners. In fact, apparent homosexual individuals are known from all of the traditional domestic species, from sheep, cattle and horses to cats, dogs and budgerigars.


Basis

Sexual behaviors often require a significant energy investment. When sexual behaviors produce offspring, there is an obvious benefit for the animal. However, the benefit from performing homosexual behaviors (which cannot result in the production of offspring) is less obvious, and some scientists have called it a "Darwinian paradox" because it is non-reproductive. A number of non-exclusive different explanations for the emergence of such traits have been put forward.


Physiological basis

A definite
physiological Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemica ...
explanation or reason for homosexual activity in animal species has not been agreed upon by researchers in the field. Numerous scholars are of the opinion that varying levels (either higher or lower) of the sex hormones in the animal, in addition to the size of the animal's gonads, play a direct role in the sexual behavior and preference exhibited by that animal. Others firmly argue no evidence to support these claims exists when comparing animals of a specific species exhibiting homosexual behavior exclusively and those that do not. Ultimately, empirical support from comprehensive endocrinological studies exist for both interpretations. Researchers found no evidence of differences in the measurements of the gonads, or the levels of the sex hormones of exclusively homosexual
western gulls The western gull (''Larus occidentalis'') is a large white-headed gull that lives on the west coast of North America. It was previously considered conspecific with the yellow-footed gull (''Larus livens'') of the Gulf of California. The wester ...
and ring-billed gulls. Additional studies pertaining to hormone involvement in homosexual behavior indicate that when administering treatments of testosterone and estradiol to female heterosexual animals, the elevated hormone levels increase the likelihood of homosexual behavior. Additionally, boosting the levels of sex hormones during an animal's pregnancy appears to increase the likelihood of it birthing a homosexual offspring.


Genetic basis

Researchers found that disabling th
fucose mutarotase
(FucM) gene in laboratory mice – which influences the levels of
estrogen Estrogen or oestrogen is a category of sex hormone responsible for the development and regulation of the female reproductive system and secondary sex characteristics. There are three major endogenous estrogens that have estrogenic hormonal ac ...
to which the brain is exposed – caused the female mice to behave as if they were male as they grew up. "The mutant female mouse underwent a slightly altered developmental programme in the brain to resemble the male brain in terms of sexual preference" said Professor Chankyu Park of the Korea Advanced Institute of Science and Technology in Daejon, South Korea, who led the research. His findings were published in the ''BMC Genetics'' journal on July 7, 2010. Another study found that by manipulating a gene in fruit flies (''
Drosophila ''Drosophila'' () is a genus of flies, belonging to the family Drosophilidae, whose members are often called "small fruit flies" or (less frequently) pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many speci ...
''), homosexual behavior appeared to have been induced. However, in addition to homosexual behavior, several abnormal behaviors were also exhibited apparently due to this mutation.


Neurobiological basis

In March 2011, research showed that
serotonin Serotonin () or 5-hydroxytryptamine (5-HT) is a monoamine neurotransmitter. Its biological function is complex and multifaceted, modulating mood, cognition, reward, learning, memory, and numerous physiological processes such as vomiting and va ...
is involved in the mechanism of sexual orientation of mice. A study conducted on fruit flies found that inhibiting the dopamine neurotransmitter inhibited lab-induced homosexual behavior.


Other hypotheses

One proposal for the adaptive function of homosexual behavior is the formation of alliances and mutual social benefit to the animals. Studies support this in specific species, such as
black swans Black swan is the common name for ''Cygnus atratus'', an Australasian waterfowl. (The) Black Swan(s) may also refer to: Film and television * ''The Black Swan'' (film), a 1942 swashbuckler film * ''Black Swans'' (film), a 2005 Dutch drama film * ' ...
, where a quarter of mate pairs consist of two males, who mate with a female and chase her away once she lays the egg, then raise it themselves. These M-M pairs have great success in defending their territory and resources, and keep their young alive until fledgling 80% of the time, compared to 30% for M-F pairs. Studies done on homosexual behavior in birds showed a negative correlation between relative parental investment and F-F homosexual behaviors, i.e. females that invested more time and care into their young relative to males had less homosexual encounters. Similarly, there was a negative correlation between relative parental investment and M-M homosexual behaviors. This meant that species exhibiting a high degree of
polygamy Crimes Polygamy (from Late Greek (') "state of marriage to many spouses") is the practice of marrying multiple spouses. When a man is married to more than one wife at the same time, sociologists call this polygyny. When a woman is marr ...
(where females often are the exclusive caretakers of the young) F-F sexual behaviors were very rare, whereas in a socially
monogamous Monogamy ( ) is a form of dyadic relationship in which an individual has only one partner during their lifetime. Alternately, only one partner at any one time ( serial monogamy) — as compared to the various forms of non-monogamy (e.g., pol ...
species (in which a M-F pair works together to care for young) they were much more common. The trend was opposite for males, in polygamous species M-M sexual behaviors were quite common and in socially monogamous species they were rare. The study argues that release from parental care, a very energy intensive investment, allows the opportunities for homosexual behaviors to be exhibited, and higher parental care prevents homosexual behaviors from occurring because of the energy cost of the behaviors. A 2019 paper hypothesized that when sex first began to evolve, there was no distinction between homosexuality and
heterosexuality Heterosexuality is romantic attraction, sexual attraction or sexual behavior between people of the opposite sex or gender. As a sexual orientation, heterosexuality is "an enduring pattern of emotional, romantic, and/or sexual attractions" ...
, and animals mated with other members of their species indiscriminately. This is a contrast to most perspectives, which try to find explanations for the evolution of homosexual behaviors and separate it completely from the evolution of heterosexual behaviors. The study states that it is unlikely that sexual behaviors evolved simultaneously to the evolution of traits necessary to recognize a compatible sexual mate, such as size, shape, odor, and color. As those secondary sex characteristics evolved, sexuality would have become more discriminatory, leading to less homosexuality, but homosexual behaviors would rarely have had enough cost to be selected against and removed entirely from a population. Additionally, the cost of homosexual behavior would be offset by the cost of mate recognition, which requires psychological adaptations, and excessive discrimination in mate choice can lead to missing out of mating opportunities. With indiscriminate mating, these factors are irrelevant. The paper notes that in some species, especially where survival is very difficult and each energy-related decision could mean the animal's death, homosexual behavior would be strongly selected against, leading strictly heterosexual species.


Some select species and groups


Birds


Black swans

An estimated one-quarter of all
black swan The black swan (''Cygnus atratus'') is a large waterbird, a species of swan which breeds mainly in the southeast and southwest regions of Australia. Within Australia, the black swan is nomadic, with erratic migration patterns dependent upon ...
pairings are of males. They steal nests, or form temporary threesomes with females to obtain eggs, driving away the female after she lays the eggs. The males spent time in each other's society, guarded the common territory, performed greeting ceremonies before each other, and (in the reproductive period) pre-marital rituals, and if one of the birds tried to sit on the other, an intense fight began. More of their
cygnet A cygnet is a young swan. Cygnet may also refer to: Places * Cygnet Island, a small islet in south-eastern Australia *Cygnet, Ohio, a village in the United States *Cygnet River, South Australia, a locality on Kangaroo Island * Cygnet, Tasmania, ...
s survive to adulthood than those of different-sex pairs, possibly due to their superior ability to defend large portions of land. The same reasoning has been applied to male
flamingo Flamingos or flamingoes are a type of wading bird in the family Phoenicopteridae, which is the only extant family in the order Phoenicopteriformes. There are four flamingo species distributed throughout the Americas (including the Caribbea ...
pairs raising chicks.


Albatrosses

Female Laysan albatrosses, on the north-western tip of the island of Oahu, Hawaii, form pairs for co-growing offspring. On the observed island, the number of females considerably exceeds the number of males (59% N=102/172), so 31% of females, after mating with males, create partnerships for hatching and feeding chicks. Compared to male-female couples, female partnerships have a lower hatching rate (41% vs 87%) and lower overall reproductive success (31% vs. 67%). Warming waters from
climate change In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to ...
have led to increased foraging times and thus increased mortality among female black-browed albatrosses on the Antipodes Islands in
New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island coun ...
. The skewed gender imbalance has led to many male albatrosses forming homosexual relationships. Male-male pairs now comprise between 2 - 5% of the albatross population on the islands.


Blue ducks

In 2009, a UK-based
captive breeding Captive breeding, also known as captive propagation, is the process of plants or animals in controlled environments, such as wildlife reserves, zoos, botanic gardens, and other conservation facilities. It is sometimes employed to help species tha ...
program for blue ducks (involving two males and one female) was derailed when the two males paired with each other instead of with the female that they were assigned to mate with.


Ibises

Research has shown that the environmental pollutant
methylmercury Methylmercury (sometimes methyl mercury) is an organometallic cation with the formula . It is the simplest organomercury compound. Methylmercury is extremely toxic, and its derivatives are the major source of organic mercury for humans. It i ...
can increase the prevalence of homosexual behavior in male
American white ibis The American white ibis (''Eudocimus albus'') is a species of bird in the ibis family, Threskiornithidae. It is found from Virginia via the Gulf Coast of the United States south through most of the coastal New World tropics. This particular ibis ...
. The study involved exposing chicks in varying dosages to the chemical and measuring the degree of homosexual behavior in adulthood. The results discovered was that as the dosage was increased the likelihood of homosexual behavior also increased. The endocrine blocking feature of mercury has been suggested as a possible cause of sexual disruption in other bird species.


Mallards

Mallard The mallard () or wild duck (''Anas platyrhynchos'') is a dabbling duck that breeds throughout the temperate and subtropical Americas, Eurasia, and North Africa, and has been introduced to New Zealand, Australia, Peru, Brazil, Uruguay, Argen ...
s form male-female pairs only until the female lays eggs, at which time the male leaves the female. Mallards have rates of male-male sexual activity that are unusually high for birds, in some cases, as high as 19% of all pairs in a population.
Kees Moeliker Cornelis W. "Kees" Moeliker (born 9 October 1960) is a Dutch biologist and director of the Natural History Museum Rotterdam. He is also European Bureau Chief of the ''Annals of Improbable Research''. Early years Moeliker's father worked for ...
of the Natural History Museum Rotterdam has observed one male mallard engage in homosexual
necrophilia Necrophilia, also known as necrophilism, necrolagnia, necrocoitus, necrochlesis, and thanatophilia, is sexual attraction towards or a sexual act involving corpses. It is classified as a paraphilia by the World Health Organization (WHO) in its ...
.


Penguins

Penguins have been observed to engage in homosexual behaviour since at least as early as 1911. George Murray Levick, who documented this behaviour in
Adélie penguin The Adélie penguin (''Pygoscelis adeliae'') is a species of penguin common along the entire coast of the Antarctic continent, which is the only place where it is found. It is the most widespread penguin species, and, along with the emperor pen ...
s at
Cape Adare Cape Adare is a prominent cape of black basalt forming the northern tip of the Adare Peninsula and the north-easternmost extremity of Victoria Land, East Antarctica. Description Marking the north end of Borchgrevink Coast and the west ...
, described it as "depraved". The report was considered too shocking for public release at the time, and was suppressed. The only copies that were made available privately to researchers had the English text partly written in Greek letters, to prevent this knowledge becoming more widely known. The report was unearthed only a century later, and published in ''
Polar Record ''Polar Record'' is a quarterly peer-reviewed academic journal covering all aspects of Arctic and Antarctic exploration and research. It is managed by the Scott Polar Research Institute and published by Cambridge University Press. The journal w ...
'' in June 2012. In early February 2004, ''
The New York Times ''The New York Times'' (''the Times'', ''NYT'', or the Gray Lady) is a daily newspaper based in New York City with a worldwide readership reported in 2020 to comprise a declining 840,000 paid print subscribers, and a growing 6 million paid ...
'' reported that Roy and Silo, a male pair of chinstrap penguins in the
Central Park Zoo The Central Park Zoo is a zoo located at the southeast corner of Central Park in New York City. It is part of an integrated system of four zoos and one aquarium managed by the Wildlife Conservation Society (WCS). In conjunction with the Centra ...
in
New York City New York, often called New York City or NYC, is the List of United States cities by population, most populous city in the United States. With a 2020 population of 8,804,190 distributed over , New York City is also the L ...
, had successfully hatched and fostered a female chick from a fertile egg they had been given to incubate. Other
penguin Penguins (order Sphenisciformes , family Spheniscidae ) are a group of aquatic flightless birds. They live almost exclusively in the Southern Hemisphere: only one species, the Galápagos penguin, is found north of the Equator. Highly adap ...
s in New York zoos have also been reported to have formed same-sex pairs. In Odense Zoo in Denmark, a pair of male king penguins adopted an egg that had been abandoned by a female, proceeding to incubate it and raise the chick. Zoos in
Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the n ...
and
Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwee ...
have also documented homosexual male penguin couples. The couples have been shown to build nests together and use a stone as a substitute for an egg. Researchers at Rikkyo University in
Tokyo Tokyo (; ja, 東京, , ), officially the Tokyo Metropolis ( ja, 東京都, label=none, ), is the capital and largest city of Japan. Formerly known as Edo, its metropolitan area () is the most populous in the world, with an estimated 37.46 ...
found 20 homosexual pairs at 16 major aquariums and zoos in Japan. The Bremerhaven Zoo in Germany attempted to encourage reproduction of endangered Humboldt penguins by importing females from Sweden and separating three male pairs, but this was unsuccessful. The zoo's director said that the relationships were "too strong" between the homosexual pairs. German gay groups protested at this attempt to break up the male-male pairs but the zoo's director was reported as saying "We don't know whether the three male pairs are really homosexual or whether they have just bonded because of a shortage of females ... nobody here wants to forcibly separate homosexual couples." A pair of male Magellanic penguins who had shared a burrow for six years at the
San Francisco Zoo The San Francisco Zoo is a zoo located in the southwestern corner of San Francisco, California, between Lake Merced and the Pacific Ocean along the Great Highway. The SF Zoo is a public institution, managed by the non-profit San Francisco Zoolog ...
and raised a surrogate chick, split when the male of a pair in the next burrow died and the female sought a new mate. Buddy and Pedro, a pair of male
African penguin The African penguin (''Spheniscus demersus''), also known as Cape penguin or South African penguin, is a species of penguin confined to southern African waters. Like all extant penguins, it is flightless, with a streamlined body and wings stiffe ...
s, were separated by the Toronto Zoo to mate with female penguins. Buddy has since paired off with a female. Suki and Chupchikoni are two female African penguins that pair bonded at the
Ramat Gan Safari The Zoological Center Tel Aviv-Ramat Gan (commonly known as the Safari Ramat Gan) in the Tel Aviv District city of Ramat Gan, Israel is the largest collection of wildlife in human care in the Middle East. The 250-acre site consists of both a driv ...
in Israel. Chupchikoni was assumed to be male until her blood was tested. In 2014 Jumbs and Hurricane, two Humboldt penguins at
Wingham Wildlife Park Wingham Wildlife Park is a medium-sized wildlife park situated near Wingham in Kent, UK where it covers an area of 26 acres (13 acres of animal housing area and a further 13 acres of car parking and overflow). In 2011 the species count at the pa ...
became the center of international media attention as two male penguins who had pair bonded a number of years earlier and then successfully hatched and reared an egg given to them as surrogate parents after the mother abandoned it halfway through incubation.
Wingham Wildlife Park Wingham Wildlife Park is a medium-sized wildlife park situated near Wingham in Kent, UK where it covers an area of 26 acres (13 acres of animal housing area and a further 13 acres of car parking and overflow). In 2011 the species count at the pa ...
As of 2018, two female King penguins at Kelly Tarltons in
Auckland Auckland (pronounced ) ( mi, Tāmaki Makaurau) is a large metropolitan city in the North Island of New Zealand. The most populous urban area in the country and the fifth largest city in Oceania, Auckland has an urban population of about I ...
, New Zealand, called Thelma and Louise (named after the 1991 film) have been in a relationship for eight years, when most of the other eligible penguins switch partners each mating season, regardless of their orientation. The two penguins were both taking care of an egg that Thelma hatched, but is unknown whether it was fertilized.


Vultures

In 1998, two male griffon vultures named Dashik and Yehuda, at the
Jerusalem Biblical Zoo The Tisch Family Biblical Zoo in Jerusalem ( he, גן החיות התנ"כי בירושלים על שם משפחת טיש, ar, حديقة الحيوان الكتابية في أورشليم القدس '), popularly known as the Jerusalem Bibl ...
, engaged in "open and energetic sex" and built a nest. The keepers provided the couple with an artificial egg, which the two parents took turns incubating, and 45 days later, the zoo replaced the egg with a baby vulture. The two male vultures raised the chick together. A few years later, however, Yehuda became interested in a female vulture that was brought into the aviary. Dashik became depressed, and was eventually moved to the zoological research garden at
Tel Aviv University Tel Aviv University (TAU) ( he, אוּנִיבֶרְסִיטַת תֵּל אָבִיב, ''Universitat Tel Aviv'') is a public research university in Tel Aviv, Israel. With over 30,000 students, it is the largest university in the country. Locate ...
where he too set up a nest with a female vulture. Two male vultures at the Allwetter Zoo in Muenster built a nest together, although they were picked on and their nest materials were often stolen by other vultures. They were eventually separated to try to promote breeding by placing one of them with female vultures, despite the protests of German homosexual groups.


Pigeons

Both male and female
pigeon Columbidae () is a bird family consisting of doves and pigeons. It is the only family in the order Columbiformes. These are stout-bodied birds with short necks and short slender bills that in some species feature fleshy ceres. They primarily ...
s sometimes exhibit homosexual behavior. In addition to sexual behavior, same-sex pigeon pairs will build nests, and hens will lay (infertile) eggs and attempt to incubate them.


Mammals


Amazon dolphins

The
Amazon river dolphin The Amazon river dolphin (''Inia geoffrensis''), also known as the boto, bufeo or pink river dolphin, is a species of toothed whale classified in the family Iniidae. Three subspecies are currently recognized: ''I. g. geoffrensis'' (Amazon river ...
or
boto Boto is a Portuguese name given to several types of dolphins and river dolphins native to the Amazon and the Orinoco River tributaries. A few botos exist exclusively in fresh water, and these are often considered primitive dolphins. Classificatio ...
has been reported to form up in bands of 3–5 individuals engaging in sexual activity. The groups usually comprise young males and sometimes one or two females. Sex is often performed in non-reproductive ways, using snout, flippers and genital rubbing, without regard to gender.Bagemihl 1999, pp. 339–348. In captivity, they have been observed to sometimes perform homosexual and heterosexual penetration of the blowhole, a hole homologous with the nostril of other mammals, making this the only known example of nasal sex in the animal kingdom. The males will sometimes also perform sex with males from the tucuxi species, a type of small
porpoise Porpoises are a group of fully aquatic marine mammals, all of which are classified under the family Phocoenidae, parvorder Odontoceti (toothed whales). Although similar in appearance to dolphins, they are more closely related to narwhals a ...
.


American bisons

Courtship, mounting, and full anal penetration between bulls has been noted to occur among
American bison The American bison (''Bison bison'') is a species of bison native to North America. Sometimes colloquially referred to as American buffalo or simply buffalo (a different clade of bovine), it is one of two extant species of bison, alongside the ...
. The
Mandan The Mandan are a Native American tribe of the Great Plains who have lived for centuries primarily in what is now North Dakota. They are enrolled in the Three Affiliated Tribes of the Fort Berthold Reservation. About half of the Mandan still re ...
nation Okipa festival concludes with a ceremonial enactment of this behavior, to "ensure the return of the buffalo in the coming season". Also, mounting of one female by another (known as "bulling") is extremely common among
cattle Cattle (''Bos taurus'') are large, domesticated, cloven-hooved, herbivores. They are a prominent modern member of the subfamily Bovinae and the most widespread species of the genus '' Bos''. Adult females are referred to as cows and adult ...
. The behaviour is hormone driven and synchronizes with the emergence of estrus (heat), particularly in the presence of a bull.


Bats

More than 20 species of bat have been documented to engage in homosexual behavior. Bat species that have been observed engaging in homosexual behavior in the wild include: Bat species that have been observed engaging in homosexual behavior in captivity include the Comoro flying fox (''Pteropus livingstonii''), the Rodrigues flying fox (''Pteropus rodricensis'') and the
common vampire bat The common vampire bat (''Desmodus rotundus'') is a small, leaf-nosed bat native to Latin America. It is one of three extant species of vampire bat, the other two being the hairy-legged and the white-winged vampire bats. The common vampire bat ...
(''Desmodus rotundus''). Homosexual behavior in bats has been categorized into 6 groups: mutual homosexual grooming and licking, homosexual masturbation, homosexual play, homosexual mounting, coercive sex, and cross-species homosexual sex. In the wild, the
grey-headed flying fox The grey-headed flying fox (''Pteropus poliocephalus'') is a megabat native to Australia. The species shares mainland Australia with three other members of the genus ''Pteropus'': the little red '' P. scapulatus'', spectacled '' P. conspicilla ...
(''Pteropus poliocephalus'') engages in
allogrooming Social grooming is a behavior in which social animals, including humans, clean or maintain one another's body or appearance. A related term, allogrooming, indicates social grooming between members of the same species. Grooming is a major socia ...
wherein one partner licks and gently bites the chest and wing membrane of the other partner. Both sexes display this form of mutual homosexual grooming and it is more common in males. Males often have erect penises while they are mutually grooming each other. Like opposite-sex grooming partners, same-sex grooming partners continuously utter a "pre-copulation call", which is described as a "pulsed grating call", while engaged in this activity. In wild
Bonin flying fox The Bonin flying fox, Bonin fruit bat (''Pteropus pselaphon''), or in Japanese is a species of flying fox in the family Pteropodidae. It is endemic to four islands (Chichijima, Hahajima, North Iwo Jima, and South Iwo Jima) in Ogasawara Isla ...
es (''Pteropus pselaphon''), males perform fellatio or 'male-male genital licking' on other males. Male–male genital licking events occur repeatedly several times in the same pair, and reciprocal genital licking also occurs. The male-male genital licking in these bats is considered a sexual behavior. Allogrooming in Bonin flying foxes has never been observed, hence the male-male genital licking in this species does not seem to be a byproduct of allogrooming, but rather a behavior of directly licking the male genital area, independent of allogrooming. In captivity, same-sex genital licking has been observed among males of the Comoro flying fox (''Pteropus livingstonii'') as well as among males of the
common vampire bat The common vampire bat (''Desmodus rotundus'') is a small, leaf-nosed bat native to Latin America. It is one of three extant species of vampire bat, the other two being the hairy-legged and the white-winged vampire bats. The common vampire bat ...
(''Desmodus rotundus''). In wild Indian flying foxes (''Pteropus giganteus''), males often mount one another, with erections and thrusting, while play-wrestling. Males of the long-fingered bat (''Myotis capaccinii'') have been observed in the same position of male-female mounting, with one gripping the back of the other's fur. A similar behavior was also observed in the
common bent-wing bat The common bent-wing bat (''Miniopterus schreibersii''), also known as the Schreibers's long-fingered bat or Schreibers's bat, is a species of insectivorous bat. They appear to have dispersed from a subtropical origin and distributed throughout ...
(''Miniopterus schreibersii''). In wild little brown bats (''Myotis lucifugus''), males often mount other males (and females) during late autumn and winter, when many of the mounted individuals are
torpid Torpor is a state of decreased physiological activity in an animal, usually marked by a reduced body temperature and metabolic rate. Torpor enables animals to survive periods of reduced food availability. The term "torpor" can refer to the time ...
. 35% of matings during this period are homosexual. These coercive copulations usually include ejaculation and the mounted bat often makes a typical copulation call consisting of a long squawk. Similarly, in hibernacula of the
common noctule The common noctule (''Nyctalus noctula'') is a species of insectivorous bat common throughout Europe, Asia, and North Africa. Description The common noctule's short fur is dark brown after moulting in June (males) or July/August (females); late ...
(''Nyctalus noctula''), active males were observed to wake up from lethargy on a warm day and engage in mating with lethargic males and (active or lethargic) females. The lethargic males, like females, called out loudly and presented their buccal glands with opened mouth during copulation. Vesey-Fitzgerald (1949) observed homosexual behaviours in all 12 British bat species known at the time: "Homosexuality is common in the spring in all species, and, since the males are in full possession of their powers, I suspect throughout the summer...I have even seen homosexuality between Natterer's and Daubenton's bats (''Myotis nattereri'' and ''M. daubentonii'')."


Bottlenose dolphins

Dolphins of several species engage in homosexual acts, though it is best studied in the
bottlenose dolphin Bottlenose dolphins are aquatic mammals in the genus ''Tursiops.'' They are common, cosmopolitan members of the family Delphinidae, the family of oceanic dolphins. Molecular studies show the genus definitively contains two species: the comm ...
s. Sexual encounters between females take the shape of "beak-genital propulsion", where one female inserts her beak in the genital opening of the other while swimming gently forward. Between males, homosexual behaviour includes rubbing of genitals against each other, which sometimes leads to the males swimming belly to belly, inserting the penis in the other's genital slit and sometimes anus. Janet Mann,
Georgetown University Georgetown University is a private research university in the Georgetown neighborhood of Washington, D.C. Founded by Bishop John Carroll in 1789 as Georgetown College, the university has grown to comprise eleven undergraduate and graduate ...
professor of biology and psychology, argues that the strong personal behavior among male dolphin calves is about bond formation and benefits the species in an evolutionary context. She cites studies showing that these dolphins later in life as adults are in a sense bisexual, and the male bonds forged earlier in life work together for protection as well as locating females to reproduce with. Confrontations between flocks of bottlenose dolphins and the related species
Atlantic spotted dolphin The Atlantic spotted dolphin (''Stenella frontalis'') is a dolphin found in warm temperate and tropical waters of the Atlantic Ocean. Older members of the species have a very distinctive spotted coloration all over their bodies. Taxonomy The Atl ...
will sometimes lead to cross-species homosexual behaviour between the males rather than combat.


Elephants

African and Asian male elephants will engage in same-sex bonding and mounting. Such encounters are often associated with affectionate interactions, such as kissing, trunk intertwining, and placing trunks in each other's mouths. Male elephants, who often live apart from the general herd, often form "companionships", consisting of an older individual and one or sometimes two younger males with sexual behavior being an important part of the social dynamic. Unlike heterosexual relations, which are always of a fleeting nature, the relationships between males may last for years. The encounters are analogous to heterosexual bouts, one male often extending his trunk along the other's back and pushing forward with his tusks to signify his intention to mount. Same-sex relations are common and frequent in both sexes, with Asiatic elephants in captivity devoting roughly 45% of sexual encounters to same-sex activity.


Giraffes

Male
giraffe The giraffe is a large African hoofed mammal belonging to the genus ''Giraffa''. It is the tallest living terrestrial animal and the largest ruminant on Earth. Traditionally, giraffes were thought to be one species, '' Giraffa camelopardal ...
s have been observed to engage in remarkably high frequencies of homosexual behavior. After aggressive "necking", it is common for two male giraffes to caress and court each other, leading up to mounting and climax. Such interactions between males have been found to be more frequent than heterosexual coupling. In one study, up to 94% of observed mounting incidents took place between two males. The proportion of same sex activities varied between 30 and 75%, and at any given time one in twenty males were engaged in non-combative necking behavior with another male. Only 1% of same-sex mounting incidents occurred between females.


Marmots

Homosexual behavior is quite common in wild marmots.Bagemihl 1999, pp. 525-7. In Olympic marmots (''Marmota olympus'') and hoary marmots (''Marmota caligata''), females often mount other females as well as engage in other affectionate and sexual behaviors with females of the same species. They display a high frequency of these behaviors especially when they are
in heat The estrous cycle (, originally ) is the set of recurring physiological changes that are induced by reproductive hormones in most mammalian therian females. Estrous cycles start after sexual maturity in females and are interrupted by anestrous p ...
. A homosexual encounter often begins with a greeting interaction in which one female nuzzles her nose on the other female's cheek or mouth, or both females touch noses or mouths. Additionally, a female may gently chew on the ear or neck of her partner, who responds by raising her tail. The first female may sniff the other's genital region or nuzzle that region with her mouth. She may then proceed to mount the other female, during which the mounting female gently grasps the mounted female's dorsal neck fur in her jaws while thrusting. The mounted female arches her back and holds her tail to one side to facilitate their sexual interaction.


Lions

Both male and female
lion The lion (''Panthera leo'') is a large cat of the genus '' Panthera'' native to Africa and India. It has a muscular, broad-chested body; short, rounded head; round ears; and a hairy tuft at the end of its tail. It is sexually dimorphic; adu ...
s have been seen to interact homosexually. Male lions pair-bond for a number of days and initiate homosexual activity with affectionate nuzzling and caressing, leading to mounting and
thrusting Thrust is a reaction force described quantitatively by Newton's third law. When a system expels or accelerates mass in one direction, the accelerated mass will cause a force of equal magnitude but opposite direction to be applied to that syst ...
. About 8% of mountings have been observed to occur with other males. Pairings between females are held to be fairly common in captivity but have not been observed in the wild.


Polecats

European polecat The European polecat (''Mustela putorius''), also known as the common polecat, black polecat, or forest polecat, is a species of mustelid native to western Eurasia and North Africa. It is of a generally dark brown colour, with a pale underbelly ...
s (''Mustela putorius'') were found to engage homosexually with non-sibling animals. Exclusive homosexuality with mounting and anal penetration in this solitary species serves no apparent adaptive function.


Primates


=Bonobos

=
Bonobo The bonobo (; ''Pan paniscus''), also historically called the pygmy chimpanzee and less often the dwarf chimpanzee or gracile chimpanzee, is an endangered great ape and one of the two species making up the genus '' Pan,'' the other being the comm ...
s form a
matriarchal Matriarchy is a social system in which women hold the primary power positions in roles of authority. In a broader sense it can also extend to moral authority, social privilege and control of property. While those definitions apply in general En ...
society, unusual among apes. They are fully
bisexual Bisexuality is a romantic or sexual attraction or behavior toward both males and females, or to more than one gender. It may also be defined to include romantic or sexual attraction to people regardless of their sex or gender identity, whic ...
: both males and females engage in hetero- and homosexual behavior, being noted for female–female sex in particular, including between juveniles and adults. Roughly 60% of all bonobo sexual activity occurs between two or more females. While the homosexual bonding system in bonobos represents the highest frequency of homosexuality known in any primate species, homosexuality has been reported for all
great apes The Hominidae (), whose members are known as the great apes or hominids (), are a taxonomic family of primates that includes eight extant species in four genera: '' Pongo'' (the Bornean, Sumatran and Tapanuli orangutan); ''Gorilla'' (the ...
, as well as a number of other
primate Primates are a diverse order of mammals. They are divided into the strepsirrhines, which include the lemurs, galagos, and lorisids, and the haplorhines, which include the tarsiers and the simians ( monkeys and apes, the latter includin ...
species. Dutch primatologist Frans de Waal, who extensively observed and filmed bonobos, believed that sexual activity is the bonobo's way of avoiding conflict. Anything that arouses the interest of more than one bonobo at a time, not just food, tends to result in sexual contact. If two bonobos approach a cardboard box thrown into their enclosure, they will briefly mount each other before playing with the box. Such situations lead to squabbles in most other species. But bonobos are quite tolerant, perhaps because they use sex to divert attention and to defuse tension. Bonobo sex often occurs in aggressive contexts totally unrelated to food. A jealous male might chase another away from a female, after which the two males reunite and engage in scrotal rubbing. Or after a female hits a juvenile, the latter's mother may lunge at the aggressor, an action that is immediately followed by genital rubbing between the two adults.


=Gorillas

= Homosexual behavior among male gorillas has been studied. This behavior occurs more often in all-male bachelor packs in the wild and it is believed to play a role in social bonding. Homosexual behavior among female
mountain gorilla The mountain gorilla (''Gorilla beringei beringei'') is one of the two subspecies of the eastern gorilla. It is listed as endangered by the IUCN as of 2018. There are two populations: One is found in the Virunga volcanic mountains of Centra ...
s has also been documented.


=Japanese macaques

= With the Japanese macaque, also known as the "snow
monkey Monkey is a common name that may refer to most mammals of the infraorder Simiiformes, also known as the simians. Traditionally, all animals in the group now known as simians are counted as monkeys except the apes, which constitutes an incomple ...
", same-sex relations are frequent, though rates vary between troops. Females will form " consortships" characterized by affectionate social and sexual activities. In some troops up to one quarter of the females form such bonds, which vary in duration from a few days to a few weeks. Often, strong and lasting friendships result from such pairings. Males also have same-sex relations, typically with multiple partners of the same age. Affectionate and playful activities are associated with such relations.


=Orangutans

= Homosexual behavior forms part of the natural repertoire of sexual or sociosexual behavior of
orangutan Orangutans are great apes native to the rainforests of Indonesia and Malaysia. They are now found only in parts of Borneo and Sumatra, but during the Pleistocene they ranged throughout Southeast Asia and South China. Classified in the genu ...
s. Male homosexual behavior occurs both in the wild and in captivity, and it occurs in both adolescent and mature individuals. Homosexual behavior in orangutans is not an artifact of captivity or contact with humans.


=Monkeys

= Among monkeys,
Lionel Tiger Lionel Tiger (born February 5, 1937) is a Canadian-American anthropologist. He is the Charles Darwin Professor of Anthropology at Rutgers University and co-Research Director of the Harry Frank Guggenheim Foundation. Early life and education Bor ...
and
Robin Fox Robin Fox (born 1934) is an Anglo-American anthropologist who has written on the topics of incest avoidance, marriage systems, human and primate kinship systems, evolutionary anthropology, sociology and the history of ideas in the social scien ...
conducted a study on how
Depo-Provera Medroxyprogesterone acetate (MPA), also known as depot medroxyprogesterone acetate (DMPA) in injectable form and sold under the brand name Depo-Provera among others, is a hormonal medication of the progestin type. It is used as a method of bir ...
contraceptive Birth control, also known as contraception, anticonception, and fertility control, is the use of methods or devices to prevent unwanted pregnancy. Birth control has been used since ancient times, but effective and safe methods of birth contr ...
s lead to decreased male attraction to females.


Sheep

'' Ovis aries'' has attracted much attention due to the fact that around 8–10% of rams have an exclusive homosexual orientation. Such rams prefer to court and mount other rams only, even in the presence of estrous ewes. Moreover, around 18–22% of rams are bisexual. Several observations indicate that male–male sexual preference in rams is sexually motivated. Rams routinely perform the same courtship behaviors (including foreleg kicks, nudges, vocalizations, anogenital sniffs and
flehmen The flehmen response (; from German ''flehmen'', to bare the upper teeth, and Upper Saxon German ''flemmen'', to look spiteful), also called the flehmen position, flehmen reaction, flehmen grimace, flehming, or flehmening, is a behavior in whic ...
) prior to mounting other males as observed when other rams court and mount estrous females. Furthermore, pelvic thrusting and ejaculation often accompany same-sex mounts by rams. A number of studies have reported differences in brain structure and function between male-oriented and female-oriented rams, suggesting that sexual partner preferences are neurologically hard-wired. A 2003 study by Dr. Charles E. Roselli et al. ( Oregon Health and Science University), states that homosexuality in male sheep is associated with a region in the rams' brains which the authors call the "ovine Sexually Dimorphic Nucleus" (oSDN) which is half the size of the corresponding region in heterosexual male sheep. Scientists found that, "The oSDN in rams that preferred females was significantly larger and contained more
neurons A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa ...
than in male-oriented rams and ewes. In addition, the oSDN of the female-oriented rams expressed higher levels of
aromatase Aromatase (), also called estrogen synthetase or estrogen synthase, is an enzyme responsible for a key step in the biosynthesis of estrogens. It is CYP19A1, a member of the cytochrome P450 superfamily, which are monooxygenases that catalyze many ...
, a substance that converts
testosterone Testosterone is the primary sex hormone and anabolic steroid in males. In humans, testosterone plays a key role in the development of male reproductive tissues such as testes and prostate, as well as promoting secondary sexual characteristi ...
to
estradiol Estradiol (E2), also spelled oestradiol, is an estrogen steroid hormone and the major female sex hormone. It is involved in the regulation of the estrous and menstrual female reproductive cycles. Estradiol is responsible for the development o ...
, a form of
estrogen Estrogen or oestrogen is a category of sex hormone responsible for the development and regulation of the female reproductive system and secondary sex characteristics. There are three major endogenous estrogens that have estrogenic hormonal ac ...
which is believed to facilitate typical male sexual behaviors. Aromatase expression was no different between male-oriented rams and ewes ..The dense cluster of neurons that comprise the oSDN express
cytochrome Cytochromes are redox-active proteins containing a heme, with a central Fe atom at its core, as a cofactor. They are involved in electron transport chain and redox catalysis. They are classified according to the type of heme and its mode of ...
P450 aromatase. Aromatase
mRNA In molecular biology, messenger ribonucleic acid (mRNA) is a single-stranded molecule of RNA that corresponds to the genetic sequence of a gene, and is read by a ribosome in the process of synthesizing a protein. mRNA is created during the ...
levels in the oSDN were significantly greater in female-oriented rams than in ewes, whereas male-oriented rams exhibited intermediate levels of expression." These results suggest that "... naturally occurring variations in sexual partner preferences may be related to differences in brain anatomy and its capacity for estrogen synthesis." As noted before, given the potential unagressiveness of the male population in question, the differing aromatase levels may also have been evidence of aggression levels, not sexuality. It should also be noted that the results of this particular study have not been confirmed by other studies. The ''Merck Manual of Veterinary Medicine'' appears to consider homosexuality among sheep as a routine occurrence and an issue to be dealt with as a problem of animal husbandry. Studies have failed to identify any compelling social factors that can predict or explain the variations in sexual partner preferences of domestic rams. Homosexual orientation and same-sex mounting in rams is not related to dominance, social rank or competitive ability. Indeed, male-oriented rams are not more or less dominant than female-oriented rams. Homosexual orientation in rams is also not affected by rearing conditions, i.e., rearing males in all-male groups, rearing male and female lambs together, early exposure of adolescent males to females and early social experiences with females do not promote or prevent homosexual orientation in rams. Male-oriented partner preference also does not appear to be an artifact caused by captivity or human management of sheep. Homosexual courtship and sexual activity routinely occur among rams of wild sheep species, such as
bighorn sheep The bighorn sheep (''Ovis canadensis'') is a species of sheep native to North America. It is named for its large horns. A pair of horns might weigh up to ; the sheep typically weigh up to . Recent genetic testing indicates three distinct subsp ...
(''Ovis canadensis''), thinhorn sheep (''Ovis dalli''), mouflons and urials (''Ovis orientalis''). Usually a higher ranking older male courts a younger male using a sequence of stylized movements. To initiate homosexual courtship, a courting male approaches the other male with his head and neck lowered and extended far forward in what is called the 'low-stretch' posture. He may combine this with the 'twist,' in which the courting male sharply rotates his head and points his muzzle toward the other male, often while flicking his tongue and making grumbling sounds. The courting male also often performs a 'foreleg kick', in which he snaps his front leg up against the other male's belly or between his hind legs. He also occasionally sniffs and nuzzles the other male's genital area and may perform the flehmen response. Thinhorn rams additionally lick the penis of the male they are courting. In response, the male being courted may rub his cheeks and forehead on the courting male's face, nibble and lick him, rub his horns on the courting male's neck, chest, or shoulders, and develop an erection. Males of another wild sheep species, the Asiatic mouflons, perform similar courtship behaviors towards fellow males. Sexual activity between wild males typically involves mounting and anal intercourse. In Thinhorn sheep, genital licking also occurs. During mounting, the larger male usually mounts the smaller male by rearing up on his hind legs and placing his front legs on his partner's flanks. The mounting male usually has an erect penis and accomplishes full anal penetration while performing pelvic thrusts that may lead to ejaculation. The mounted male arches his back to facilitate the copulation. Homosexual courtship and sexual activity can also take place in groups composed of three to ten wild rams clustered together in a circle. These non-aggressive groups are called 'huddles' and involve rams rubbing, licking, nuzzling, horning, and mounting each other. Female Mountain sheep also engage in occasional courtship activities with one another and in sexual activities such as licking each other's genitals and mounting.


Spotted hyenas

The family structure of the spotted hyena is
matriarchal Matriarchy is a social system in which women hold the primary power positions in roles of authority. In a broader sense it can also extend to moral authority, social privilege and control of property. While those definitions apply in general En ...
, and dominance relationships with strong sexual elements are routinely observed between related females. Due largely to the female spotted hyena's unique urogenital system, which looks more like a penis rather than a vagina, early naturalists thought hyenas were
hermaphroditic In reproductive biology, a hermaphrodite () is an organism that has both kinds of reproductive organs and can produce both gametes associated with male and female sexes. Many taxonomic groups of animals (mostly invertebrates) do not have s ...
males who commonly practiced
homosexuality Homosexuality is Romance (love), romantic attraction, sexual attraction, or Human sexual activity, sexual behavior between members of the same sex or gender. As a sexual orientation, homosexuality is "an enduring pattern of emotional, romant ...
. Early writings such as
Ovid Pūblius Ovidius Nāsō (; 20 March 43 BC – 17/18 AD), known in English as Ovid ( ), was a Augustan literature (ancient Rome), Roman poet who lived during the reign of Augustus. He was a contemporary of the older Virgil and Horace, with whom ...
's ''
Metamorphoses The ''Metamorphoses'' ( la, Metamorphōsēs, from grc, μεταμορφώσεις: "Transformations") is a Latin narrative poem from 8 CE by the Roman poet Ovid. It is considered his '' magnum opus''. The poem chronicles the history of the ...
'' and the ''
Physiologus The ''Physiologus'' () is a didactic Christian text written or compiled in Greek by an unknown author, in Alexandria; its composition has been traditionally dated to the 2nd century AD by readers who saw parallels with writings of Clement of A ...
'' suggested that the hyena continually changed its sex and nature from male to female and back again. In '' Paedagogus'', Clement of Alexandria noted that the
hyena Hyenas, or hyaenas (from Ancient Greek , ), are feliform carnivoran mammals of the family Hyaenidae . With only four extant species (each in its own genus), it is the fifth-smallest family in the Carnivora and one of the smallest in the cl ...
(along with the
hare Hares and jackrabbits are mammals belonging to the genus ''Lepus''. They are herbivores, and live solitarily or in pairs. They nest in slight depressions called forms, and their young are able to fend for themselves shortly after birth. The g ...
) was "quite obsessed with sexual intercourse". Many Europeans associated the hyena with sexual deformity, prostitution, deviant sexual behavior, and even witchcraft. The reality behind the confusing reports is the sexually aggressive behavior between the females, including mounting between females. Research has shown that "in contrast to most other female mammals, female ''
Crocuta ''Crocuta'' is a genus of hyena containing the largest living member of the family, the spotted hyena ''(Crocuta crocuta)''. Several fossil species are known as well. Taxonomy It is still unclear whether the genus evolved in Africa or Asia, alth ...
'' are male-like in appearance, larger than males, and substantially more aggressive," and they have "been masculinized without being defeminized". Study of this unique
genitalia A sex organ (or reproductive organ) is any part of an animal or plant that is involved in sexual reproduction. The reproductive organs together constitute the reproductive system. In animals, the testis in the male, and the ovary in the female, a ...
and aggressive behavior in the female hyena has led to the understanding that more aggressive females are better able to compete for resources, including food and mating partners. Research has shown that "elevated levels of
testosterone Testosterone is the primary sex hormone and anabolic steroid in males. In humans, testosterone plays a key role in the development of male reproductive tissues such as testes and prostate, as well as promoting secondary sexual characteristi ...
in utero ''In Utero'' is the third and final studio album by American rock band Nirvana. It was released on September 21, 1993, by DGC Records. After breaking into the mainstream with their second album, ''Nevermind'' (1991), Nirvana hired Steve Albin ...
" contribute to extra aggressiveness; both males and females mount members of both the same and opposite sex, who in turn are possibly acting more submissive because of lower levels of testosterone in utero.


Reptiles


Lizards

Several species of whiptail lizard (especially in the genus '' Aspidoscelis'') consist only of females that have the ability to reproduce through
parthenogenesis Parthenogenesis (; from the Greek grc, παρθένος, translit=parthénos, lit=virgin, label=none + grc, γένεσις, translit=génesis, lit=creation, label=none) is a natural form of asexual reproduction in which growth and developmen ...
. Females engage in sexual behavior to stimulate ovulation, with their behavior following their hormonal cycles; during low levels of estrogen, these (female) lizards engage in "masculine" sexual roles. Those animals with currently high estrogen levels assume "feminine" sexual roles. Some parthenogenetic lizards that perform the courtship ritual have greater fertility than those kept in isolation due to an increase in hormones triggered by the sexual behaviors. So, even though asexual whiptail lizards populations lack males, sexual stimuli still increase reproductive success. From an
evolutionary Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variati ...
standpoint, these females are passing their full genetic code to all of their offspring (rather than the 50% of genes that would be passed in sexual reproduction). Certain species of
gecko Geckos are small, mostly carnivorous lizards that have a wide distribution, found on every continent except Antarctica. Belonging to the infraorder Gekkota, geckos are found in warm climates throughout the world. They range from . Geckos a ...
also reproduce by parthenogenesis. Some species of sexually reproducing
gecko Geckos are small, mostly carnivorous lizards that have a wide distribution, found on every continent except Antarctica. Belonging to the infraorder Gekkota, geckos are found in warm climates throughout the world. They range from . Geckos a ...
s have also been found to display homosexual behavior, e.g. the day geckos ''Phelsuma laticauda'' and ''Phelsuma cepediana''.


Tortoises

Jonathan Jonathan may refer to: *Jonathan (name), a masculine given name Media * ''Jonathan'' (1970 film), a German film directed by Hans W. Geißendörfer * ''Jonathan'' (2016 film), a German film directed by Piotr J. Lewandowski * ''Jonathan'' (2018 ...
, the world's oldest
tortoise Tortoises () are reptiles of the family Testudinidae of the order Testudines (Latin: ''tortoise''). Like other turtles, tortoises have a shell to protect from predation and other threats. The shell in tortoises is generally hard, and like oth ...
(an Aldabra giant tortoise), had been mating with another tortoise named Frederica since 1991. In 2017, it was discovered that Frederica was actually probably male all along, and was renamed Frederic.


Insects and arachnids

There is evidence of same-sex sexual behavior in at least 110 species of insects and arachnids. Scharf et al. says: "Males are more frequently involved in same-sex sexual (SSS) behavior in the laboratory than in the field, and isolation, high density, and exposure to female pheromones increase its prevalence. SSS behavior is often shorter than the equivalent heterosexual behavior. Most cases can be explained via mistaken identification by the active (courting/mounting) male. Passive males often resist courting/mating attempts". Scharf et al. continues: "SSS behavior has been reported in most insect orders, and Bagemihl (1999) provides a list of ~100 species of insects demonstrating such behavior. Yet, this list lacks detailed descriptions, and a more comprehensive summary of its prevalence in invertebrates, as well as ethology, causes, implications, and evolution of this behavior, remains lacking".


Dragonflies

Male homosexuality has been inferred in several species of
dragonflies A dragonfly is a flying insect belonging to the infraorder Anisoptera below the order Odonata. About 3,000 extant species of true dragonfly are known. Most are tropical, with fewer species in temperate regions. Loss of wetland habitat threa ...
(the
order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of ...
Odonata Odonata is an order of flying insects that includes the dragonflies and damselflies. Members of the group first appeared during the Triassic, though members of their total group, Odonatoptera, first appeared in Late Carboniferous. The two com ...
). The cloacal pinchers of male
damselflies Damselflies are flying insects of the suborder Zygoptera in the order Odonata. They are similar to dragonflies, which constitute the other odonatan suborder, Anisoptera, but are smaller and have slimmer bodies. Most species fold the wings alo ...
and dragonflies inflict characteristic head damage to females during sex. A survey of 11 species of damsel and dragonflies has revealed such mating damages in 20 to 80% of the males too, indicating a fairly high occurrence of sexual coupling between males.


Fruit flies

Male ''
Drosophila melanogaster ''Drosophila melanogaster'' is a species of fly (the taxonomic order Diptera) in the family Drosophilidae. The species is often referred to as the fruit fly or lesser fruit fly, or less commonly the " vinegar fly" or "pomace fly". Starting with ...
'' flies bearing two copies of a mutant allele in the
fruitless The ''fruitless'' gene (''fru'') is a ''Drosophila melanogaster'' gene that encodes several variants of a putative transcription factor protein. Normal ''fruitless'' function is required for proper development of several anatomical structures nec ...
gene court and attempt to mate exclusively with other males. The genetic basis of animal homosexuality has been studied in the fly ''D. melanogaster''. Here, multiple genes have been identified that can cause homosexual courtship and mating. These genes are thought to control behavior through pheromones as well as altering the structure of the animal's brains. These studies have also investigated the influence of environment on the likelihood of flies displaying homosexual behavior.


Bed bugs

Male
bed bug Bed bugs are insects from the genus ''Cimex'' that feed on blood, usually at night. Their bites can result in a number of health impacts including skin rashes, psychological effects, and allergic symptoms. Bed bug bites may lead to skin changes ...
s (''Cimex lectularius'') are sexually attracted to any newly fed individual and this results in homosexual mounting. This occurs in heterosexual mounting by the traumatic insemination in which the male pierces the female abdomen with his needle-like penis. In homosexual mating this risks abdominal injuries as males lack the female counteradaptive spermalege structure. Males produce alarm pheromones to reduce such homosexual mating.


See also


References


External links


National GeographicHomosexual Behaviour in Animals An Evolutionary PerspectiveDriscoll, E. V. (2008), Bisexual Species, Scientific American Mind, 19(3), pp. 68–73.
{{DEFAULTSORT:Homosexual Behavior In Animals Sexual orientation and science Ethology Animal sexuality Articles containing video clips Homosexuality