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I've been trying to track down the source of a claim that research has shown giraffe exhibiting a really high rate of male homosexual relations. Going through the blog spam leads me to a site without any references claiming to publish on science, stating:

Do you know the percentage of homosexual behavior in male giraffes? It is whooping 94%. Female giraffes too exhibit homosexual behavior; however, it is just 1%. Few homosexual behaviors among male giraffes include necking, caressing, courting and mounting.

Is there any research supporting this claim?

  • Looks like the source, according to Wikipedia is "Bruce Bagemihl, Biological Exuberance: Animal Homosexuality and Natural Diversity, St. Martin's Press, 1999; pp.391-393." Anyone on their way to the library? – Oddthinking Mar 12 '12 at 14:50
  • @Oddthinking: you can start by watching Ricky Gervais' take on it (moderately NSFW. Depending where you work, I guess) youtube.com/watch?v=dO45GrfSmWg – nico Mar 12 '12 at 19:02
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Data is scarce, but there is definitely a lot of homosexual behavior among giraffes

From what I can tell by other places this claim is made on the web, the common source is Bruce Bagemihl's famous book, Biological Exuberance (1999). On p. 34-5 it states:

Three different species exemplify some of the issues that are involved in just one measure of frequency, the proportion of activity that is homosexual. Observed versus actually occurring behaviors in Giraffes, seasonal variations in sexual activity in Mountain Sheep, and alternative standards of reference in Gray Herons complicate the calculation of homosexual frequency in each of these species. During an exhaustive study of Giraffes in the Arush and Tarangire National Parks of Tanzania, researchers recorded 17 homosexual mounts and 1 heterosexual mount in more than a year (and 3,200 hours) of observation. Thus, 94 percent of all observed mounting activity was same-sex. Does this reflect the actual proportion of homosexual activity in Giraffes? Certainly more than on heterosexual mating occurred during that time, since over 20 calves were born that year in one population alone. However, these populations did have relatively low birth rates, and heterosexual mating appeared to be genuinely rare. In addition, if heterosexual matings were missed by the observers, probably homosexual ones were as well.

In a footnote he gives the source and considers another study:

Giraffe (Pratt and Anderson 1985, 1982, 1979). In a study of another population of giraffes, only three mounts between males were recorded, but only 400 hours of observation were involved (Dagg and Foster 1976:124).

Can't view the whole bibliography entry on Google Books, but I could swing by the library tonight and find it if someone expresses interest.

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    In addition, if heterosexual matings were missed by the observers, probably homosexual ones were as well. I think this may be a conclusion that is not necessarily supported by facts. In dogs the act of mounting is a dominance thing and the mounting is more about showing the dominance to the pack. I would suspect(without proof granted) that this is the behavior that was observed. The fact that the team missed at least 95% of the heterosexual matings would also infer gaps in their methodlogy. – Chad Mar 12 '12 at 17:05
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    @Chad: You seem to be raising two issues. One is whether 3200 hours of observation was enough to get a fair sampling - that would largely depend on whether it was random and didn't influence behaviour, and less about the >95% of matings missed. The second is whether the behaviour was actually sexual (which I suspect, is more about definitions than anything else). – Oddthinking Mar 12 '12 at 23:25
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    @Oddthinking - Actually I would say the definition simple. Is there sexual coupling or is it simulated. As for the number of hours I suspect the problem relies more on methodology of collection rather than number of hours. – Chad Mar 13 '12 at 13:15
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    @Oddthinking - Are you really going to make me say penetration? Anyway I am not saying that there is a problem. But statistically that heterosexual coupling did not happen (it is within the margin of error and can be discounted as an abboration). Yet clearly (based on the fact that their were 20 babies that season) heterosexual behavior happens regularly unless giraffes reproduce homosexually. This leads me to suspect problems with the study methodology. – Chad Mar 13 '12 at 14:56
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    Please note these are criticisms of the study not the answer. – Chad Mar 13 '12 at 14:58
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I looked up the sources mentioned above:

Pratt DM and VH Anderson. 1982. Population, distribution and behavior of giraffe in the Arusha National Park, Tanzania. Journal of Natural History 16 pp481-489

This article is about population data collected over a year of observation. It mentions there have been 22 births in that year, a low birth rate considering the population included 172 females. It says nothing about mating or homosexual behavior.

Pratt DM and VH Anderson. 1985. Giraffe social behavior. Journal of Natural History 19 pp771-781.

This article summarizes the authors' observations and statistics of social interaction in giraffes, collected in three separate national parks in Northen Tanzania, over about 3 years of total (non-consecutive) observations, more precisely 3264 hours of observation. They mention that they integrate findings from the '79 and the '82 articles in this summary article.

They say that sparring bouts, which usually involve "necking", when giraffes swing their necks and hit each other with them, sometimes included one male attempting to mount another. "We saw this eight times in the Arusha Park and eight times at Tarangire. In nine of these 16 events, the animal attempting to mount had his penis unsheathed. [...] In no case did a bull try to mount another male as large as himself. Intent observation and detailed recording of positions and movements failed to show that this act was an expression of dominance (which we initially surmised); we never saw any indications---e.g., behavioural, postural--of submission in bulls mounted."

The article goes on to discuss courtship and mating. It appears that it's very rare for giraffes to actually mate. The female is in heat only one day out of every two weeks. The males test females for readiness by sniffing their urine, but the female can choose who to give this data (by choosing to urinate or not when the male lowers his head to her rump). When a male giraffe senses that a female is in the right condition, they may proceed to courtship, which involved 1-2 days worth of following her closely and occasionally attempting to mount, which the female usually frustrates by just walking forward. When the female chooses to stand still, the mounting will proceed. The researchers note with some exasperation that over their 3 years of observation, they only saw one successful mounting, out of 46 courtship attempts and 304 urine-sniffing attempts. In light of the fact that in one of these years 22 calves were born as discussed in the previous article, they must have missed many - but of course they could also miss many homosexual mounting attempts.

Dagg, AI and Foester JB. 1976. The giraffe, its biology, behavior and ecology. New York, Van Nostrand Reinhold.

This book briefly mentions that homosexual mounting was frequent (no numbers) in one park where the number of females was unusually low, about 30%; in another park with approximate parity between the sexes, it was much more rare, and they only saw 3 attempts in 400 hours of observation.

"Necking" is not treated as homosexual behavior by any of these sources; they mention that necking is reserved only for males, and seems related to dominance relationships between males.

My conclusion from all this is that although it's arithmetically true that in 3 years of observation, the authors of the '85 source saw 16 homosexual mountings and just one mating, it might be misleading to summarize that as "94% of sexual activity is homosexual". First, the observation apparently missed the vast majority of matings, and probably of homosexual mounting as well. Second, the male giraffes seemed interested in much more coupling, but the menstrual cycle and female refusal combined to give them only incredibly rare opportunities.

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Bagemihl cites 3 sources of which bibliographic particulars were not available. I believe it is:

  1. Pratt DM and VH Anderson. 1982. Population, distribution and behavior of giraffe in the Arusha National Park, Tanzania. Journal of Natural History 16 pp481-489
  2. Pratt DM and VH Anderson. 1985. Giraffe social behavior. Journal of Natural History 19 pp771-781. I do not see an article by Pratt and anderson in 1979.
  3. Dagg, AI and Foester JB. 1976. The giraffe, its biology, behavior and ecology. New York, Van Nostrand Reinhold.

The source:

The figure of 94% may be in the 3 articles, but I do not have access to it. Logic tells me that no species of which sexual behaviour is 94% homosexual will survive. The observations were simply inadequate. Further, Simmons and Scheepers propose that the giraffe's long neck originates from intrasexual competition and not from the alternative theory of feeding behaviour. Males with the sturdiest and longest necks passed their genes on. For them, necking is agonistic and not affiliative behaviour.

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    "Logic tells me that no species of which sexual behaviour is 94% homosexual will survive" - Why is that? You only need to mate once a season to have babies. "94% of matings are homosexual" is not the same as "94% of giraffes are exclusively homosexual." – BlueRaja - Danny Pflughoeft May 13 '13 at 22:56
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Anne Innis Dagg studied giraffe in the wild in the late 50's & early 60's. She observed and documented lots of male homosexual behavior. She authored "The giraffe : its biology, behavior and ecology" in 1976 & much later, "Pursuing Giraffe", which is about her experiences as a woman zoologist at that time, & some of the resistance to her observing and reporting on homosexual behavior.

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    Can you add some of the relevant quotes from the sources for those of us who do not have access to them? – rjzii Sep 22 '13 at 19:07

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