Male Gorillas Make a Splash to Woo Females, New Study Finds
for National Geographic News
|July 19, 2001|
Scientists have found that male gorillas in the
forests of northern Congo (Brazzaville) deliberately splash about in
swampland clearings to intimidate their competitors in the battle to woo
The discovery is the first evidence of a wild
animal using its body to manipulate water for a visual effect.
"If you see a 160-kilogram (353-pound) silverback charging into the river, you are unlikely to lead to the conclusion that he is bathing," said Richard Parnell, a primate researcher at the University of Stirling, United Kingdom. "It is a very forceful display."
Parnell and his colleague Hannah Buchanan-Smith studied the behavior of western lowland gorillas at Mbeli Bai, a swampy clearing in the Congo where at least 14 gorilla families come to feed. The gorillas visit the area regularly to eat aquatic herbs, some of which are high in sodium.
The frequency of those visits makes the site a good place for researchers to observe the gorillas and study the interactions among families and individuals. Parnell and Buchanan-Smith monitored the gorillas' behavior over a 32-month period that ended in 1999.
The insight they acquired is especially intriguing because researchers have generally found it difficult to get close to western lowland gorillas in the dense forests of the Congo, so knowledge about their social behavior is quite limited.
From their observations at Mbeli Bai, the researchers discovered that the wide-open swampland was more than just a feeding ground. In human terms, an analogy might be a pick-up joint, like a hotdog stand at the beach on a hot summer day.
"The bai is a great place to check out females," said Parnell.
A male who's searching for a female companion might go the clearing to feed on the swampy vegetation but also to watch members of gorilla groups that stop by. What the solitary male gorilla appears to be hoping for, the researchers say, is an opportunity to hook up with a female.
To strengthen his chances of being the one chosen by a female, a male often intimidates other males by heartily displaying his splashing prowess. The behavior is so pronounced the researchers could observe it from a fairly long distance.
"We are pretty confident that the behavior is tied to aggressive display where [the male gorilla] is saying something about himselfannouncing his presence and saying he is not to be messed with," said Parnell.
The gorillas perform basically three different kinds of splashing: one- and two-handed splashes, and a body splash.
The body splash is much like a "cannonball," in which people run and jump into a swimming pool. The gorillas, however, don't tuck their legs under them when they jump, as people do.
In one- and two-handed splashes, the animals raise one or both arms and strike the surface of the water with their palms open and slightly angled.
The splashing behavior was seen most often in single adult males who were not with a group of their own (relative to their number in the population). These single, adult males were also the target of most splashing displays.
Young gorillas sometimes play in the water, but the splashing conduct of the adult gorillas was limited to males. Adult females never engaged in splashing.
The use of water as a tool for communication is thought to be extremely rare among land-based mammals. The only other evidence of splashing behavior something like that of the gorillas in the Congo came from studies of a chimpanzee community in Tanzania. The chimps were found to throw rocks into streams apparently also as an act of intimidation.
The discovery that western lowland gorillas use water to communicate suggests that they are able to adapt to their environment to achieve their goalsin this case, to intimidate potential rivals.
An act of intimidation that almost all wild gorillas engage in is charging toward a rival but veering away at the last moment, then smacking their palms down on the ground with a thump.
The researchers say that while all gorillas exhibit the charging and ground-slap behavior, that act and the splashing behavior are different enough to suggest that the western lowland gorillas have adapted to an aquatic environment.
In a paper in the July 16 issue of Nature describing their splashing study, the scientists said: "We anticipate that gorillas, maligned as cognitively poor cousins to the other great apes, will emerge from further bai studies as adaptable, innovative, and intelligent creatures that exploit a complex environment."
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