Cooperative hunting roles among taï chimpanzees

All known chimpanzee populations have been observed to hunt small mammals for meat. Detailed observations have shown, however, that hunting strategies differ considerably between populations, with some merely collecting prey that happens to pass by while others hunt in coordinated groups to chase fast-moving prey. Of all known populations, Taï chimpanzees exhibit the highest level of cooperation when hunting. Some of the group hunting roles require elaborate coordination with other hunters as well as precise anticipation of the movements of the prey. The meat-sharing rules observed in this community guarantee the largest share of the meat to hunters who perform the most important roles leading to a capture. The learning time of such hunting roles is sometimes especially long. Taï chimpanzee males begin hunting monkeys at about age 10. The hunters’ progress in learning the more sophisticated hunting roles is clearly correlated with age; only after 20 years of practice are they able to perform them reliably. This lengthy learning period has also been shown in some hunter-gatherer societies and confirms the special challenge that hunting represents.     

Insect and meat eating among infant and adult baboons (Papio cynocephalus) of Mikumi National Park, Tanzania

It has been suggested that baboon predation upon vertebrates may tend to peak in the dry season because insect food is then less available, and that males obtain animal nutrients primarily from vertebrates whereas other troop members obtain them primarily from invertebrates. The development of meat and insect eating by 22 male and 24 female infants studied for 25 months was compared with that of 18 male and 46 female adults studied for 37 months. Systematic sampling allowed quantitative comparisons between meat and insect eating, infants and adults, and males and females. Infants ate no meat, but their insect eating began early and increased steadily during the first year of life. In comparison with insect foods, meat was a minor ingredient of the adult's diet. Insect eating occurred less during dry than during rainy months, but meat eating was spread across the year. Reliable sex differences in insect eating did not occur. The findings were related to theories offered to explain the attractiveness of animal foods to primates and to the suggestion that a sex difference in predatory inclinations of hominid ancestors may have been a preadaptation underlying the eventual emergence of male hunting and female gathering.     

Predation on giant flying squirrels (Petaurista philippensis) by black crested gibbons (Nomascus concolor jingdongensis) at Mt. Wuliang, Yunnan, China

Predation on vertebrates is infrequent in gibbons. In a 14-month field study of the central Yunnan black crested gibbon (Nomascus concolor jingdongensis) at Mt. Wuliang, Yunnan, China, we observed gibbons attacking, killing and eating giant flying squirrels (Petaurista philippensis). During 845 h of observation on one study group, the gibbons attacked giant flying squirrels 11 times, and succeeded in 4 cases. Although all members of the group attempted to attack the squirrels, all four successful attacks were made by the same adult female. The victims were infants in three cases and a juvenile or sub-adult in one case. Black crested gibbons also attacked adult giant flying squirrels by grabbing their long tails and throwing them from the canopy, but they failed to catch or kill the prey in three cases observed. Passive meat sharing occurred in three out of four successful cases. Besides hunting giant flying squirrels, the black crested gibbons also ate eggs or chicks in two birds’ nests and one lizard.     

Age-related differences in foraging behavior of Montagu's harrier<Emphasis Type="Italic"> Circus pygargus</Emphasis> males in south-east Poland

The hunting behaviour and habitat use of second-calendar-year males (subadult) and grey (adult) males of Montagu's harrier Circus pygargus were compared in south-east Poland. Subadult males performed cruising flights less frequently than did adult males. In contrast, subadult males more frequently soared thermals and were harassed more often by other birds. Overall, adult males were more frequently engaged in hunting activities than subadult males. Additionally, adult males were more successful in trapping prey than were subadult males. Only 7% (n=92) of trapping attempts by subadult males were successful, compared with 17% (n=126) by grey males. Both adult and subadult males tried to catch prey flushed by foxes Vulpes vulpes. Subadult males were seen begging and pirating from prey-carrying raptors. Communicated by M.E. dos Santos     

‘Impact hunters’ catalyse cooperative hunting in two wild chimpanzee communities

Even when hunting in groups is mutually beneficial, it is unclear how communal hunts are initiated. If it is costly to be the only hunter, individuals should be reluctant to hunt unless others already are. We used 70 years of data from three communities to examine how male chimpanzees ‘solve’ this apparent collective action problem. The ‘impact hunter’ hypothesis proposes that group hunts are sometimes catalysed by certain individuals that hunt more readily than others. In two communities (Kasekela and Kanyawara), we identified a total of five males that exhibited high hunt participation rates for their age, and whose presence at an encounter with red colobus monkeys increased group hunting probability. Critically, these impact hunters were observed to hunt first more often than expected by chance. We argue that by hunting first, these males dilute prey defences and create opportunities for previously reluctant participants. This by-product mutualism can explain variation in group hunting rates within and between social groups. Hunting rates declined after the death of impact hunter FG in Kasekela and after impact hunter MS stopped hunting frequently in Kanyawara. There were no impact hunters in the third, smaller community (Mitumba), where, unlike the others, hunting probability increased with the number of females present at an encounter with prey.     

Further data on predation by free-ranging Stumptail macaques (Macaca arctoides)

Additional data on systematic and occasional hunting of insects, water snails, reptiles, and birds by free-ranging Stumptails are reported. Adult males participated in hunting and meat-eating. However, the hunt was dominated by the adult females and by dominant individuals. Meat-sharing between mother and offspring, between hunter and close-friends, and piece-dropping types were observed. In general almost all troop members including infants displayed an interest in meat eating. Supported by the Mexican Institute of Anthropology and by the Behavioral Science Foundation of Mexico.     

Hunting Behavior of Chimpanzees at Ngogo,Kibale National Park,Uganda

Chimpanzees (Pan troglodytes) prey on a variety of vertebrates, mostly on red colobus (Procolobus spp.) where the two species are sympatric. Variation across population occurs in hunting frequency and success, in whether hunting is cooperative, i.e., payoffs to individual hunters increase with group size, and in the extent to which hunters coordinate their actions in space and time, and in the impact of hunting on red colobus populations. Also, hunting frequency varies over time within populations, for reasons that are unclear. We present new data on hunting by chimpanzees at Ngogo, Kibale National Park, Uganda, and combine them with earlier data (Mitani and Watts, 1999, Am. J. Phys. Anthropol. 109: 439–454) to examine hunting frequency and success, seasonality, and cooperation. The Ngogo community is the largest and has the most males of any known community. Chimpanzees there mostly hunt red colobus and are much more successful and make many more kills per hunt than at other sites; they kill 6–12% of the red colobus population annually. The number of kills and the offtake of meat per hunt increase with the number of hunters, but per capita meat intake is independent of hunting party size; this suggests that cheating occurs in large parties. Some behavioral cooperation occurs. Hunting success and estimated meat intake vary greatly among males, partly due to dominance rank effects. The high overall success rate leads to relatively high average per capita meat intake despite the large number of consumers. The frequency of hunts and of hunting patrols varies positively with the availability of ripe fruit; this is the first quantitative demonstration of a relationship between hunting frequency and the availability of other food, and implies that the chimpanzees hunt most when they can easily meet energy needs from other sources. We provide the first quantitative support for the argument that variation in canopy structure influences decisions to hunt red colobus because hunts are easier where the canopy is broken.     

Range expansion as a response to increasing group size in the Yunnan snub-nosed monkey

The Yunnan snub-nosed monkey (Rhinopithecus bieti) is characterized by a larger home range and group size than other colobine species. We investigated variations in home range size of a free-ranging group of R. bieti from 1998 to 2007 in the Baimaxueshan National Nature Reserve in Yunnan, China. Group size increased from 160 to 450 over the 10 years. Results also showed a home range shift and yearly home range expansion, although this expansion was very limited. The study group covered a 33.78-km(2) area during the 10-year period, with some areas abandoned and others used repeatedly. The yearly home range increase stopped in 2004 and decreased thereafter. Despite increasing group size usually being coupled with larger yearly home range (>30 km(2)), the group confined itself within a relatively small and stable area (<18 km(2)) during 2005-2007, with a significant portion of their accessible home range discarded. Consequently, the study group showed the highest recorded population density among extant groups of R. bieti. Reasons why the group settled into a substantially smaller home range area remain unclear.     

云南龙马山滇金丝猴(Rhinopithecus bieti)冬季食性分析

2006年11月-2007年12月,对云南云龙县龙马山滇金丝猴(Rhinopithecus bieti)冬季食性进行了研究.采用粪便显微组织学分析技术分析龙马山滇金丝猴冬季采食植物的种类组成和比例,并测定了该猴群主要取食的15种植物(包括两种松萝科植物)(取食食物百分比>1%)和次要取食的10种植物(取食食物百分比<1%)的化学成分.研究结果表明,龙马山滇金丝猴冬季取食的植物共计26科45种,其中云龙箭竹、长松萝、花松萝、实竹、空心箭竹分别占19.78%、10.28%、8.37%、4.93%、4.46%,是滇金丝猴冬季主要取食的植物种类,占取食植物的47.99%.木本植物和草本植物的叶是滇金丝猴的主要食物,在冬季食物中所占百分比最高,达75%.冬季滇金丝猴比较喜欢采食P/F值较高、单宁含量较低的食物,其主要食物比次要食物含有较高的P/F值和较低的单宁(P<0.05).     

Hunting income patterns among the Hadza: big game, common goods, foraging goals and the evolution of the human diet.

The assumption that large mammal hunting and scavenging are economically advantageous to hominid foragers is examined in the light of data collected among the Hadza of northern Tanzania. Hadza hunters disregard small prey in favour of larger forms (mean adult mass greater than or equal to 40 kg). Here we report experimental data showing that hunters would reduce their mean rates if they included small animals in the array they target. Still, daily variance in large animal hunting returns is high, and the risk of failure correspondingly great, significantly greater than that associated with small game hunting and trapping. Sharing large kills reduces the risk of meatless days for big game hunters, and obviates the problem of storing large amounts of meat. It may be unavoidable if large carcasses cannot be defended economically against the demands of other consumers. If so, then large prey are common goods. A hunter may gain no consumption advantage from his own big game acquisition efforts. We use Hadza data to model this 'collective action' problem, and find that an exclusive focus on large game with extensive sharing is not the optimal strategy for hunters concerned with maximizing their own chances of eating meat. Other explanations for the emergence and persistence of this practice must be considered.     

Observations on the meat-eating behavior of wild bonobos (Pan paniscus) at Wamba,Republic of Zaire

Meat-eating behavior of wild bonobos (Pan paniscus) was witnessed on two occasions at Wamba, Republic of Zaire. Only flying squirrels were observed to be eaten by the bonobos. Several bonobos gathered around the possessor of the meat and showed interest in the meat on all occasions. Begging behavior was noted on one of the two occasions, but the possessor of the meat ignored it. No sharing of meat was seen on either occasion. The exclusive targets of hunting by bonobos are apparently small mammals, such as flying squirrels and infant duikers, since evidence of meat eating by wild bonobos, which have been studied for more than fifteen years, has been restricted to these mammals. The bonobos at Wamba may have a specialized “prey image”, as in the case of the chimpanzees (Pan troglodytes) of the Tai forest, and certain medium-sized or small mammals may not conform to this image.     

Meat eating in wild hamadryas baboons: Opportunistic trade‐offs between insects and vertebrates

The consumption of meat may provide herbivorous animals with important nutrients that are scarce in their plant‐based diet. Seasonal variation in plant food availability has been suggested to motivate dietary flexibility in a range of species and thus primates may seek more prey when key plant resources are unavailable. Alternatively, prey encounter rate may drive meat eating. Here we investigate patterns of meat eating in hamadryas baboons (Papio hamadryas) at Filoha, Awash National Park, Ethiopia. The Filoha baboons rely largely on doum palm fruit (Hyphaene thebaica), which are available most months of the year, and the young leaves of Acacia senegal, which are more abundant during the wet season. We hypothesized that the baboons would consume more meat when H. thebaica and A. senegal were less available, which we tested by comparing meat eating and consumption of these plant food species from March 2005 through February 2006. Our results reveal a high rate of vertebrate meat eating at Filoha (0.028/hour of observation) compared with other hamadryas sites. We found no relationship, however, between meat eating (either insect or vertebrate) and either rainfall or consumption of H. thebaica or A. senegal, indicating that availability of preferred plant resources does not drive meat consumption. Vertebrate consumption and time spent feeding were significantly negatively associated; there was no relationship, however, between the consumption of animal matter and either home range size or daily path length. Vertebrate and insect consumption alternated throughout the year such that the baboons maintained a small amount of animal matter in their diet year‐round. Our results suggest that the baboons do not often actively seek animal matter, but consume it opportunistically, with the presence of locust and dragonfly swarms driving insect consumption, and both prey availability and the availability of feeding time shaping vertebrate predation.     

Benefits of Group Foraging Depend on Prey Type in a Small Marine Predator,the Little Penguin

Group foraging provides predators with advantages in over-powering prey larger than themselves or in aggregating small prey for efficient exploitation. For group-living predatory species, cooperative hunting strategies provide inclusive fitness benefits. However, for colonial-breeding predators, the benefit pay-offs of group foraging are less clear due to the potential for intra-specific competition. We used animal-borne cameras to determine the prey types, hunting strategies, and success of little penguins (Eudyptula minor), a small, colonial breeding air-breathing marine predator that has recently been shown to display extensive at-sea foraging associations with conspecifics. Regardless of prey type, little penguins had a higher probability of associating with conspecifics when hunting prey that were aggregated than when prey were solitary. In addition, success was greater when individuals hunted schooling rather than solitary prey. Surprisingly, however, success on schooling prey was similar or greater when individuals hunted on their own than when with conspecifics. These findings suggest individuals may be trading-off the energetic gains of solitary hunting for an increased probability of detecting prey within a spatially and temporally variable prey field by associating with conspecifics.     

Vertebrate Predation and Food-Sharing in Cebus and Pan

Capuchins and chimpanzees are the only nonhuman primates apart from baboons known to prey systematically upon relatively large vertebrates. Vertebrate predation is common and well documented in Pan troglodytes, rare in Pan paniscus, and commonly reported but infrequently studied in Cebus. Food-sharing is common in both Pan species but rarely reported for wild capuchins. I present data on vertebrate predation and food-sharing by white-faced capuchins (Cebus capucinus) from ongoing field studies at Santa Rosa National Park, Costa Rica. We have observed 106 successful predation events resulting in the capture of 156 prey items during 2929 observation hr (5.35 prey per 100 hr). Squirrels and nestling coatis comprised half of the prey taken; the remainder were mainly nestling birds and eggs. Adult males took 52% of all prey and 67% of squirrels. Squirrels are actively hunted and about 65% of them are adults. I estimated that the average capuchin group kills 43–50 squirrels annually, mostly during the dry season. Capuchins hunt squirrels in groups 81% of the time, and 17% of hunts are successful. There is no evidence for cooperative hunting, but occasional collaboration is suggested. Rates of food-sharing were low (1.7 per 100 hr), and meat was the only food shared between adults. I compare predation and food-sharing in C. capucinus with published data for Pan troglodytes, primarily in Gombe and Taï National Parks. I discuss sex differences, hunting strategies, the relationship between hunting and food-sharing, and various ecological and social factors that may promote vertebrate predation in Pan and Cebus.     

Phylogeography and population structure of the Yunnan snub-nosed monkey (Rhinopithecus bieti) inferred from mitochondrial control region DNA sequence analysis

Rhinopithecus bieti, the Yunnan snub-nosed monkey, is the nonhuman primate with the highest altitudinal distribution and is also one of the 25 most globally endangered primate species. Currently, R. bieti is found in forests between 3000 and 4500 m above sea level, within a narrow area on the Tibetan Plateau between the Yangtze and Mekong rivers, where it is suffering from loss of habitat and shrinking population size (approximately 1500). To assess the genetic diversity within this species, its population structure and to infer its evolutionary history, we sequenced 401 bp of the hypervariable I (HVI) segment from the mitochondrial DNA control region (CR) for 157 individuals from 11 remnant patches throughout the fragmented distribution area. Fifty-two variable sites were observed and 30 haplotypes were defined. Compared with other primate species, R. bieti cannot be regarded as a taxon with low genetic diversity. Phylogenetic analysis partitioned haplotypes into two divergent haplogroups (A and B). Haplotypes from the two mitochondrial clades were found to be mixed in some patches although the distribution of haplotypes displayed local homogeneity, implying a strong population structure within R. bieti. Analysis of molecular variance detected significant differences among the different geographical regions, suggesting that R. bieti should be separated into three management units (MUs) for conservation. Based on our results, it can be hypothesized that the genetic history of R. bieti includes an initial, presumably allopatric divergence between clades A and B 1.0-0.7 million years ago (Ma), which might have been caused by the Late Cenozoic uplift of the Tibetan Plateau, secondary contact after this divergence as a result of a population expansion 0.16-0.05 Ma, and population reduction and habitat fragmentation in the very recent past.     

Ecological selection and sexual dimorphism in the sooty oystercatcher,Haematopus fuliginosus

Male and female sooty oystercatchers (subspecies Haematopus fuliginosus fuliginosus; Haematopodidae) have an average difference in bill length of 19%. We studied the relationship between this sexual dimorphism and foraging ecology at coastal sites in southern New South Wales, Australia. Intersexual foraging divergence was most striking in diet, with seven prey classes eaten exclusively by one sex (male: 4, female: 3), and all shared prey classes eaten in different proportions. Intersexual diet partitioning was also observed in energetic rewards gained from foraging, with females gaining highest energetic benefits from eating ascidians and males from eating limpets. Furthermore, within the most commonly consumed prey item, limpets, females gained higher energetic benefit from eating smaller sizes while males gained greater rewards from the largest limpet sizes. Intersexual divergence was also observed in several aspects of foraging behaviour. Finally, there was a significant effect of tidal cycles upon intersexual niche partitioning in this species; the degree of diet divergence varied between tide conditions and females had a consistently more efficient dietary intake on neap tides than males. Diet divergence in the sooty oystercatcher is greater than previously observed in any oystercatcher, and is correlated with the largest sexual bill dimorphism recorded in this family. It is argued that intersexual competition between territorial pairs is operating to diverge male and female bill morphology.     

Further studies on predation by chimpanzees of the Mahale Mountains

Chimpanzees of the M-group in the Mahale Mountains, Tanzania, were seen to commit predation 15 times between May 1978 and July 1979. The data appear to suggest that they come to perform predation frequently in recent years. However, for evaluating long-term changes in their predatory disposition, several factors must be considered, such as changes in research formation, in the degree of habituation of the chimpanzees and in the influence of humans on prey animals. These factors should be also considered when the findings of various populations are compared. It seems that an adult male can more easily control his desire for exclusive possession of meat than that of plant-food. Adult males have priority over females in obtaining meat, but all of the former cannot join the meat-eating cluster. Besides the dominance rank, dyadic relationships between them may regulate whether an adult male can join it. This suggests that all adult males in a unit-group may not be tied by an equal bond. The evolutionary implications of chimpanzee predation are discussed on the basis of the assumption that both chimpanzee predation and human hunting originated in some habit of a common ancestor.     

Hunting rates and hunting success in the spotted hyena (Crocuta crocuta)

Hunting group size, hunting rates and hunting success were monitored over a seven-year period among members of one large clan of spotted hyenas ( Crocuta crocuta ) inhabiting the Masai Mara National Reserve, in south-west Kenya. Prey availability varied seasonally in this study area, and hyenas tended to hunt whichever prey species were most abundant during each month of the year. Over 75% of 272 hunting attempts were made by lone hyenas, even when they hunted antelope three times their own body mass, such as wildebeest and topi. Of all prey that were commonly hunted, only zebra were usually hunted in groups. Approximately one-third of all hunting attempts resulted in prey capture. Although no significant sex differences were observed in juvenile or adult hunting rates, low-ranking adult females hunted at significantly higher hourly rates than did higher-ranking females. Hunting success was not influenced by the social rank of hunters, but hunting group size and hunter's age strongly influenced success. Young hyenas were poor hunters, and did not achieve adult competency levels until they were 5–6 years old.     

First report of prey capture from human laid snare-traps by wild chimpanzees

Chimpanzees regularly hunt for meat in the wild, including both solo and group hunting; however, theft of prey from non-chimpanzee hunters, or scavenging of carcasses is extremely rare. Here we report the first observations of a novel prey capture technique by the chimpanzees in two adjacent communities in the Budongo Conservation Field Station, Uganda. In both cases blue duikers were found caught in human laid snare traps, and then retrieved by the chimpanzees. In one case the duiker was still alive when retrieved and subsequently fully consumed by the chimpanzees. In the other, the chimpanzees encountered the duiker while alive, but retrieved it soon after its death; here only a small portion was consumed. These observations are discussed in comparison to observations of chimpanzee hunting, scavenging, and their exploitation of an environment increasingly modified by human activity.     

To feed or to wrap? Female silk cues elicit male nuptial gift construction in a semiaquatic trechaleid spider

By wrapping prey and offering it as a nuptial gift, males can obtain mating and/or parental benefits despite some costs. Males of the Neotropical semiaquatic spider Paratrechalea ornata (Trechaleidae) offer females a nuptial gift consisting of a prey item wrapped in silk. What stimulus inhibits males from feeding and elicits gift construction? We hypothesized that signals associated with female silk threads could affect decision-making by males. We investigated three groups of males carrying a captured prey under different experimental treatments. In the treatment S, males were exposed to an arena with female silk; in SF, males were exposed to both silk and a female confined in a cell, and in the control group, males were exposed to a clean arena. Gift construction was observed only in the S and SF groups, with a similar occurrence rate. After touching females (SF group), males did not change their pattern of gift construction. Gift construction occurrence increased with male and female age. The results lead us to assume that the existence of chemical cues associated with female silk elicits male searching behaviour and gift construction, allowing males to decide between eating or wrapping prey according to the possibility of a sexual encounter. Anticipating gift construction, males are ready to mate, diminishing the risks of predation, female desertion or male–male scramble competition. The effect of age on behavioural variation and the rate of construction is discussed.