Is 94% of male giraffe sexual behaviour homosexual?

Question

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?

Answer 1

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.

Answer 2

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:

• Simmons RE and Scheepers L. 1996. Winning by a neck: sexual selection in the evolution of Giraffe. The American Naturalist 148(5) pp781-786.

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.