Published online 14 February 2008 | Nature | doi:10.1038/news.2008.578

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Apes photographed having face-to-face sex in the wild.

Caught on camera: Leah and George in a face-to-face romantic session. Thomas Breuer – WCS/MPI-EVA

Western gorillas (Gorilla gorilla) copulating in the wild have only ever been seen facing the same way as each other, front to back. But in a forest clearing in the Nouabale-Ndoki National Park in the Republic of Congo, a female gorilla, Leah, and her groups’ dominant male silverback, George, have been photographed in the face-to face position.

This type of behaviour has only ever been seen in the wild in the bonobo (Pan paniscus), as well as a single, brief, unphotographed observation in mountain gorillas (G. beringei).

In captivity, gorillas often have sex face-to-face, but it is difficult to draw conclusions about ape behaviour from these animals; they are brought up in a very different environment in captivity, says Thomas Breuer, from the Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany.

Doubly famous

Leah has been seen displaying extraordinary behaviour before — in 2005 she was spotted using a stick as a tool to test the depth of a lake. (see Gorillas branch out into tool use) But this double-dose of fame is unlikely to be because Leah is particularly special, says Breuer. Instead, it is probably because she is one of only three females in a group of gorillas that has been watched closely for the past 13 years by scientists from the Wildlife Conservation Society.

The scientists tend to get 'snapshots' of the gorillas' behaviour, says Breuer, as the animals can be seen clearly only in open areas. “99% of the time they spend in the forest,” he says. So it is hard to know whether this face-to-face encounter is normal in other environmental conditions.

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The swampy clearing where the gorillas had their tête-à-tête might be the reason for the unusual sexual position, says Breuer — the swamp acts as a sort of water-bed, forcing the gorillas to behave in unusual ways, such as walking upright rather than on all fours.

Did Leah and George know they were being watched? The gorillas are aware of the observation platform up in the trees, says Breuer, but seem mostly undisturbed by the scientists’ presence.