Darkness cloaked the Dzanga forest clearing in the Central African Republic, broken only by the faint light of a crescent moon. The January night was still and quiet, except for the usual background hum of crickets and frogs. Then, a different kind of noise rose from the din—loud and low rumbles, accompanied by roars and groans. After a minute or two, the cacophony dissipated, and the clearing returned more or less to its familiar drone.
To the naked eye, the theatrics behind the sounds would have been imperceptible in the blackness. But peering through a heat-sensing camera, behavioral ecologist Peter Wrege witnessed a sharp, fluorescent view of the action: a group of African forest elephants (Loxodonta cyclotis) engaged in a kind of pachyderm pandemonium.
The ruckus is triggered by a mating event. After a male and female have consummated, adults, juveniles, and calves run over to the mated couple, smelling and tasting the seminal and vaginal fluids on the ground and screaming in what seems like excitement. “You can tell from the sound—lots of different elephants are excited about this mating,” says Wrege. (See the behavior in the video below.)
Researchers first documented mating pandemonium in 1988 in savanna elephants—the better-known relative of forest elephants—at Amboseli National Park in Kenya. But because the events happen primarily during the evening, “unless you had really, really bright moonlight or very bright starlight, you couldn’t see any detail,” says Wrege, director of Cornell’s Elephant Listening Project
As a result, while heard loud and clear, the uproars went relatively unseen until Wrege and his team observed the drama through the lens of a thermal imaging camera in 2012. So far, the group is the only one to have used the technology to look into mating pandemonium events.
Unlike other forms of night vision, thermal imaging derives an image strictly from the subject’s body heat and requires no light to function. Invented for the military in the 1950s, the technique made its debut in wildlife studies in the early ‘70s. Since then, biologists use it mainly to monitor animal health, count populations, and record behavior, says thermal biologist Dominic McCafferty, who uses thermal imaging to investigate body temperature in marine mammals and birds. “Body temperature is one of the most fundamental physiological parameters,” he says, because it can reveal information about an animal’s metabolism, stress level, and presence of infection or disease.
When Wrege looked at elephants on his thermal video recorder's screen, each animal's unique body temperature displayed as colors ranging from white and yellow at one end of the spectrum, to purple and indigo at the other. The first night that Wrege witnessed mating pandemonium in thermal color, it was pitch black outside. “I couldn’t see my hand in front of my face,” he says, and “it was really a shock when I turned on the camera and my screen was full of colored elephants.” (The mating elephants appear more yellow, or hotter, compared to the rest of the elephants.)
Why so many elephants seemingly enthuse over the mating of others still remains largely unknown. Wrege suggests that the behavior might allow a female elephant to announce her peak fertility to additional males after she’s mated with a first bull. Alternatively, fellow group members might use these events to evaluate the health and status of a mated male by smelling his semen, or the health of a female by smelling her vaginal fluids, suggests Wrege.
Using thermal imaging, Wrege’s team can better study forest elephant mating by connecting pachyderm calls to behaviors that they otherwise wouldn’t be able to see. There seems to be a lot of mating going on at night, says Wrege, and without thermal imaging to study it, “we’re really not painting the whole picture of elephant biology.” (This thermal project was supported by the U.S. Fish and Wildlife Service.)
While mating pandemonium events are what he’s most eager to further study, Wrege is also hopeful that thermal imaging can help curb hunting of forest elephants. “Right now poaching for ivory is really out of hand [in the Central African Republic],” says Wrege. When forests elephants emerge into a clearing—to mate, for instance—they become more vulnerable. By figuring out where and when mating happens, conservationists could determine which areas to concentrate on protecting.
*This article was updated on August 5, 2014 to reflect the support of the U.S. Fish and Wildlife Service in Wrege's thermal work.