Wild chimpanzees deprived a leopard of its kill: Implications for the origin of hominin confrontational scavenging.

This study reports the first observed case of wild chimpanzees (Pan troglodytes) obtaining animal prey freshly killed by a sympatric leopard (Panthera pardus) and scavenging it with the leopard still nearby. This observation has important implications for the emergence of confrontational scavenging, which may have played a significant role in human evolution. Many scholars agree that eating meat became important during human evolution, and hominins first obtained meat by scavenging. However, it is debatable whether scavenging behavior was "passive" or "confrontational (power)." The latter is more dangerous, as it requires facing the original predator, and it is thus considered to have been important for the evolution of several human traits, including cooperation and language. Chimpanzees do scavenge meat, although rarely, but no previous evidence of confrontational scavenging has hitherto emerged. Thus, it was assumed that they are averse to confrontation with even leopard-sized predators. However, in the observed case the chimpanzees frequently emitted waa barks, which indicated that they were aware of the leopard's presence but they nevertheless continued to eat the scavenged meat. In addition, we compiled and reviewed 49 cases of chimpanzee encounters with animal carcasses in the Mahale Mountains of Tanzania in 1980-2017. Chimpanzees scavenged meat in 36.7% of these cases, and tended to eat the meat when it was fresh or if the animal species was usually hunted by chimpanzees. However, no evidence indicated that carcasses were avoided when leopard involvement was likely. These results suggest that chimpanzee-sized hominins could potentially confront and deprive leopard-size carnivores of meat.

A newborn infant chimpanzee snatched and cannibalized immediately after birth: Implications for "maternity leave" in wild chimpanzee.

OBJECTIVES: This study reports on the first observed case of a wild chimpanzee infant being snatched immediately after delivery and consequently cannibalized by an adult male in the Mahale Mountains, Tanzania. We demonstrate "maternity leave" from long-term data from the Mahale M group and suggest that it functions as a possible counterstrategy of mother chimpanzees against the risk of infanticide soon after delivery. MATERIALS AND METHODS: The subjects of this study were the M group chimpanzees at Mahale Mountains, Tanzania. The case of cannibalism was observed on December 2, 2014. We used the long-term daily attendance record of the M group chimpanzees between 1990 and 2010 to calculate the lengths of "maternity leave," a perinatal period during which a mother chimpanzee tends to hide herself and gives birth alone. RESULTS: We observed a very rare case of delivery in a wild chimpanzee group. A female chimpanzee gave birth in front of other members, and an adult male snatched and cannibalized the newborn infant immediately after birth. Using the long-term data, we demonstrate that the length of "maternity leave" is longer than that of nonmaternity leave among adult and adolescent female chimpanzees. DISCUSSION: We argue that this cannibalism event immediately after birth occurred due to the complete lack of "maternity leave" of the mother chimpanzee of the victim, who might lack enough experience of delivery. We suggest that "maternity leave" taken by expecting mothers may function as a possible counterstrategy against infanticide soon after delivery.

Ranging behavior of Mahale chimpanzees: a 16 year study.

We have analyzed the ranging patterns of the Mimikire group (M group) of chimpanzees in the Mahale Mountains National Park, Tanzania. During 16 years, the chimpanzees moved over a total area of 25.2 or 27.4 km(2), as estimated by the grid-cell or minimum convex polygon (MCP) methods, respectively. Annually, the M group used an average of 18.4 km(2), or approximately 70 %, of the total home-range area. The chimpanzees had used 80 % of their total home range after 5 years and 95 % after 11 years. M group chimpanzees were observed more than half of the time in areas that composed only 15 % of their total home range. Thus, they typically moved over limited areas, visiting other parts of their range only occasionally. On average, the chimpanzees used 7.6 km(2) (in MCP) per month. Mean monthly range size was smallest at the end of the rainy season and largest at the end of the dry season, but there was much variability from year to year. The chimpanzees used many of the same areas every year when Saba comorensis fruits were abundant between August and January. In contrast, the chimpanzees used several different areas of their range in June. Here range overlap between years was relatively small. Over the 16 years of the study we found that the M group reduced their use of the northern part of their range and increased their frequency of visits to the eastern mountainous side of their home range. Changes in home-range size correlated positively with the number of adult females but not with the number of adult males. This finding does not support a prediction of the male-defended territory model proposed for some East African chimpanzee unit-groups.

Natural history of Camponotus ant-fishing by the M group chimpanzees at the Mahale Mountains National Park, Tanzania.

The aim of this study was to provide basic data on ant-fishing behavior among the M group chimpanzees at the Mahale Mountains National Park, Tanzania. Ant-fishing is a type of tool-using behavior that has been exhibited by Mahale chimpanzees when feeding upon arboreal carpenter ants (Camponotus spp.) since the 1970s, and is now regarded as a candidate of wild chimpanzee culture. Herein, I describe in detail the features of ant-fishing shown by the Mahale M group chimpanzees: (1) 2 species of Camponotus ants (Camponotus sp. (chrysurus-complex) [C. sp.1] and C. brutus) were identified as the target species of ant-fishing, and C. sp.1 was selected intensively as the main target; (2) 24 species (92 individuals) of trees were identified as ant-fishing sites-these were widely distributed throughout the western/lowland region of the M group's home range, and the top 5 species were used more frequently; (3) the efficiency of ant-fishing was influenced not only by the site choice or the skillfulness of the chimpanzees, but inevitably by the condition of the ants; (4) the estimated nutritional intake from ant-fishing was apparently negligible; (5) most of the M group members (50/60 individuals) older than 3 years of age successfully used tools to fish for ants; and (6) female chimpanzees engaged in ant-fishing more frequently and for longer periods than males did. Further, I compared the features of ant-fishing exhibited by the Mahale M group chimpanzees with those exhibited by the former K group at Mahale and by other populations of wild chimpanzees.

Prevalence of muzzle-rubbing and hand-rubbing behavior in wild chimpanzees in Mahale Mountains National Park, Tanzania.

In 1998, four chimpanzees in the Mahale Mountains National Park, Tanzania, were observed wiping their mouths with non-detached leaves or stalks of grass, or rubbing their mouths with a tree trunk or branch, especially while eating lemons. The number of mouth-wiping/rubbing individuals increased to 18 in 1999. By 2005, 29 chimpanzees were documented wiping/rubbing their muzzles in this way. Although it is difficult to determine whether the chimpanzees acquired this behavior as a result of trial and error or social learning, the fact that chimpanzees at other sites perform this behavior with detached leaves or leafy twigs much more often than with intact items suggests the possibility that cleaning with intact plant parts at Mahale spread via social learning.

Tool-use for drinking water by immature chimpanzees of Mahale: prevalence of an unessential behavior.

Use of leaves or sticks for drinking water has only rarely been observed during long-term study of wild chimpanzees (Pan troglodytes schweinfurthii) at Mahale. Recently, however, we observed 42 episodes of tool-use for drinking water (73 tools and two cases of using "tool-sets") between 1999 and 2004. Interestingly, all of the performers were immature chimpanzees aged from 2 to 10 years. Immature chimpanzees sometimes observed the tool-using performance of others and subsequently reproduced the behavior, while adults usually paid no attention to the performance. This tool-use did not seem to occur out of necessity: (1) chimpanzees often used tools along streams where they could drink water without tools, (2) they used tools for drinking water from tree holes during the wet season when they could easily obtain water from many streams, and (3) the tool-using performance sometimes contained playful aspects. Between-site comparisons revealed that chimpanzees at drier habitats used tools for drinking water more frequently and in a more "conventional" manner. However, some variations could not be explained by ecological conditions. Such variations and the increase in this tool-use in recent years at Mahale strongly suggest that social learning plays an important role in the process of acquiring the behavior. We should note here that such behaviors that lack obvious benefits or necessity can be prevalent in a group.