In the study of primate sexuality, one of the most interesting examples is that of the bonobo, also known as the Pygmy Chimpanzee. Dr. Susan Block calls these animals "the horniest apes on earth" and explains that the "highly sexed females are also far more likely to initiate sex with the males than any other great ape females (including humans!)" (link)
Bonobo society, in which females are dominant, centers around sex. Some speculate that the use of sex to solve problems causes bonobos to be one of the least violent primates. According to Dr. Block, bonobos "tend to resolve any conflicts they might have by mounting each other or engaging in oral or manual sex" (link). Bonobos have sex often, usually several times a day.
Douglas Foster writes:
Sex patterns among bonobos also reveal remarkable patterns of behavior. Bonobos engage in carefree erotic exchanges of unusual frequency and form. Face-to-face mating was once considered a distinctly human activity, but male and female bonobos often use the "missionary position," according to field studies and captive animal observation in zoos around the world. Bonobos also engage in polymorphous pleasures, including erotic rubbing between females, penis fencing among males, cross-generational sex play, group eroticism, and French kissing.
"The bonobo is a sexual Olympian," writes Natalie Angier in Woman, An Intimate Geography. "Males, females, old, callow, no matter — it’s sex, grope, hump, genito-genital rub-a-dub-dubbing, all the day long." (link)
Bonobos also engage in lesbian sex, as this article by Frans B. M. de Waal, originally published in Scientific American, explains:
Perhaps the bonobo's most typical sexual pattern, undocumented in any other primate, is genito-genital rubbing (or GG rubbing) between adult females. One female facing another clings with arms and legs to a partner that, standing on both hands and feet, lifts her off the ground. The two females then rub their genital swellings laterally together, emitting grins and squeals that probably reflect orgasmic experiences.
Bonobos may have a lot of sex, but encounters are short by human standards, with "the average copulation lasting 13 seconds." (link) And whereas humans seem to prefer to go out to dinner first and have sex afterwards, bonobos reverse the order of this, apparently to defuse the tension surrounding competition over food. But it isn't just the presence of food that instigates sex among bonobos. It is also the presence of, well, just about anything. De Waal explains:
[. . .] anything, not just food, that arouses the interest of more than one bonobo at a time 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.
I picture a bonobo looking over at the zookeeper and making gestures meaning, "Hey! Throw another one of those carboard boxes in here!"