Cage design attenuates display patterns of male chimpanzees

Chimpanzee (Pan troglodytes) males are well known for their frequent displays toward viewers who approach and stand in front of their cages. If the front of the chimpanzees' cage is vertical and is constructed of bars or chain link framed by steel, the display includes “pant-hooting,” then lunging onto the cage's front, followed by a series of vigorous attempts to shake the entire structure. The display is intimidating and can include spitting and throwing of materials. Also, displays can incur substantial damage to the cage over time. By sloping the front of the cage toward the center of the cage, the display pattern is profoundly attenuated both in frequency and form. Additionally, it serves to make the males more tranquil. No adverse effects on their health and well-being over a 2-year period have been noted.     

Social influences on ranging patterns among chimpanzees (Pan troglodytes verus) in the Tai National Park, Cote d'Ivoire

Group size is expected to be an important factor to predicthome-range (HR) size in social animals. In chimpanzees adultmales play an important role in defending the HR against neighbors,and therefore it has been suggested that HR size depends onthe number of adult males. In this long-term study on wild WestAfrican chimpanzees, we analyzed the relative importance ofcommunity size and composition on ranging patterns over a 10-yearperiod, using multivariate statistics. Because community sizedecreased from 51 individuals with 6 adult males in 1992 to22 individuals with only 1 adult male in 2001, we expected adecrease in HR size, which should be better predicted by thenumber of males than by community size. We further investigatedthe effect of fruit availability on monthly HRs over a 4-yearperiod. As predicted, HR size decreased during the first 7 yearsof our study but increased during the last 3 years. Overall,the number of adult males was the best predictor of HR size,whereas fruit availability did not correlate with HR size. HRuse remained stable over the entire study period, with a constantproportion of about 35% of the HR used as core area. High HRand core-area overlap values between different years indicatedstrong site-fidelity. Although the number of males within thecommunity explained the decrease in HR size, the recent increasein size remains unexplained. This finding suggests that otherfactors such as relative fighting power of males affect HR size.     

Pygmy chimpanzee association patterns in ranging

The spatial distribution and its change of a pygmy chimp population was studied. The association patterns of the population demonstrated the existence of a bisexual group whose members associate almost exclusively with one another. Further within the group there were cohesive subgroups consisting of both sexes. The bisexual subgroups were related to female clusters whose members share the smaller range than that of the group. Frequent associations among male and female pygmy chimps largely modified the general tendency that females use smaller areas than males. Social units common to two species of chimps are bisexual groups which give the outer frames for the formation of associations and also for the range use.     

Within-group cannibalism by adult male chimpanzees

In the Mahale Mountains National Park, Tanzania, a young adult male chimpanzee was observed to feed on a 3-month-old male infant of the same unit-group. Four other adult males and an adult female shared the carcass. The mother of the victim had immigrated from a neighboring unit-group four years previously. Circumstantial evidence strongly suggests that the first-observed cannibal male also killed the infant. The adult male and the mother of the victim had been familiar socially and sexually with each other since the female immigrated. Since the mother of the victim had usually been ranging in the peripheral part of the unit-group's range, i.e., the overlapping area of the two unit-group's ranges during pregnancy and soon after birth, the infanticidal male might have had reason to suspect the paternity of her infant. Four such cases of within-group cannibalism by adult males suggest that the female range and association pattern before and after parturition are key factors allowing an infant to survive. The possibility of male-biased infanticide is also discussed.     

Comparison of the communicative vocalizations and behaviors of group ranging in eastern gorillas,chimpanzees and pygmy chimpanzees

Field observations were carried out on chimpanzees, pygmy chimpanzees and eastern gorillas. Since the communicative behaviors which appear in group ranging are closely related to the grouping of the animals and to the social structure, the communicative behaviors of group ranging were compared in the above three species in order to elucidate the common and different characters of their three much diversified social structures. The following conclusions were drawn: (1) the common ancestor ofGorilla andPan had the territorial call “hoot” and behavior of display, and males were antagonistic between each other in the society; (2) the common ancestral species did not have any special long distance cohesive calling: the society was a small compact one, moving on the ground; and (3) the social structure of the pygmy chimpanzee is very different from the common ancestral social structure when compared with those of the gorilla and chimpanzee, in that the pygmy chimpanzee has lost the behaviors of strong antagonistic character between adult males.     

Procedures for improving maternal behavior in captive chimpanzees

Captive female chimpanzees who have had no opportunity to observe mothers with infants or to interact with infants often show inappropriate maternal behavior, particularly with their first-born infant, and this usually results in the removal of the infant to be human-reared. The present study used two techniques to encourage appropriate maternal behavior in ten pregnant female chimpanzees. These females were housed together with unrelated infant chimpanzees to adopt, or with lactating female chimpanzees and infants to observe. In five cases both techniques were used, in two cases only the first technique was used, and in three cases only the second technique was used. All ten female chimpanzees showed appropriate maternal behavior when their infants were born, in contrast to a group of eight female chimpanzees who had no such experience whose infants had to be removed for human-rearing. It is suggested that these techniques, or adaptations of them, could be applied to many other captive female chimpanzees with similar results.     

Mahale chimpanzees: grouping patterns and cycling females

The social system of chimpanzees (Pan troglodytes schweinfurthii) is characterized by the fission-fusion of social groups. Several studies have reported that females are less gregarious than males. In the current study, adult female gregariousness depended on their reproductive state. Noncycling adult females (pregnant, lactating, or post reproductive) were observed in large bisexual parties less often than cycling adult females. On the other hand, cycling adult females were observed in large bisexual parties as often as males, regardless of their estrous state. More males were in parties that included cycling adult females with maximal genital swelling (estrous females) than in parties without them. Moreover, a bisexual party including more estrous females contained more males. These results suggest that large bisexual parties of chimpanzees are constructed by a dual mechanism. First, cycling adult females are attracted to parties that consist of the top ranking male and large numbers of adult and adolescent males. Second, adult and adolescent males that did not belong to parties originally are attracted by estrous females and join them. Thus, in Mahale Mountains National Park, Tanzania, bisexual parties of chimpanzees can be characterized as "parties for reproduction."     

Sex difference and postnatal change of maternal behavioral patterns in juvenile male and female rats

Juvenile rats are known to show certain elements of maternal behavior. In this experiment, to investigate sex difference and postnatal change of retrieving and pup-cleaning (licking) behaviors in juvenile rats, these behaviors were recorded using new observation method at 20, 30 and 45 days of age in female and male Wistar rats. At 20 days of age, maternal behavior was observed in a common plastic observation cage (test A) and then test B was performed. In the test B, observation was carried out using a cage with a wooden box that was open on one side, helping the juveniles to establish a nest. As the results of day 20, most rats in all groups showed licking behavior in both the test A and B. The incidence of retrieving behavior increased from the test A to the test B with the box in both sexes, especially in males (p<0.01). The box is thought to play a facilitative role in induction of retrieving. Moreover, the incidence in males was higher than that in females in the test B (p<0.001). At 30 and 45 days of age, only a test B with box was performed. The incidences of licking and retrieving behaviors at 30 days of age were decreased significantly compared to those at 20 days of age in both sexes(p<0.001). Further decrease from 30 days to 45 days was observed. These results suggest that in juvenile rat, incidence of retrieving behavior in males is higher than that in females but there is no sex difference in incidence of licking behavior. Potency to show these behaviors decreases acutely before puberty in rats.     

Reproductive memory for diagonal and nondiagonal patterns in chimpanzees

Two male juvenile chimpanzees were trained to reproduce from memory geometric patterns composed of lighted cells in a 3 x 3 matrix. In Experiment I, subjects reproduced 3-cell horizontal, vertical and diagonal patterns with either 0- or 5-second delay between stimulus offset and response. Diagonals were more difficult and were more affected by delay than were nondiagonal patterns. The sequence of response to diagonals was less structured than to nondiagonals. In Experiment II, more complex 4-cell patterns were used and, following training, subjects were tested for transfer to new patterns. Again, diagonals were more difficult to reproduce than nondiagonals. Transfer of training to new patterns requiring different motoric responses was successful. Similar to Experiment I, organization of responding was greater for nondiagonals than for diagonals. These results are discussed with regard to the presence of internal representation of visual information in nonhuman primates.     

Association,ranging, and the social unit in chimpanzees of the Mahale Mountains,Tanzania

In order to characterize the social unit in chimpanzees, about which several conflicting views have been proposed, the proximity matrix among 55 recognized chimpanzees and the range covered by each of them are examined, on the basis of data obtained at the Mahale Mountains during 12 months in 1978–1979. It is shown once again that chimpanzees have a bisexual social unit (unit-group). Two such unit-groups were detected in the study area. All animals belonged to one of the two unit-groups except a few cycling females (and a juvenile male accompanied by his cycling mother) which were seen to associate alternately with members of two neighboring unit-groups, covering a whole range of one or even two unit-groups. The problem of such females is discussed in relation to the spatial relationships between the two unit-groups. Reexamining the membership of a unit-group, it is demonstrated that a unit-group was most likely patrilineal. While nulliparous females transferred between unit-groups, parous females tended to remain in a unit-group where they first gave birth to infants and to have several offspring therein. This appeared significant for ensuring recruitment of members of the next generation to a patrilineal unit-group. Although some adult males left their natal unit-group, they never joined the other. Male departure from a unit-group seemed to be forced by the other males and to be the sociological equivalent of going into exile, which is unique in nonhuman primates.     

Activity and ranging patterns of Colombian woolly monkeys in north-western Amazonia

In this study, I revise three aspects of the socioecology of woolly monkeys (genus Lagothrix) that might give us a better understanding of the patterns found in this species: (1) the association between temporal variation in fruit abundance and diet, activity, and ranging patterns; (2) the individual trade-offs associated with living in small or large groups, and (3) the relationship between social dominance and foraging success. Using behavioral and ecological data collected during 3 years in Tinigua Park, Colombia, I found that woolly monkeys tend to avoid open-degraded forests, where fruit production is generally lower than it is in mature forests. Diet and activity budgets were highly associated with temporal patterns of fruit production. Daily path length was positively correlated with group size and monthly fruit abundance, and negatively correlated with habitat quality. I found differences in activity budgets and the diet preferences of different age/sex classes. For example, adult males rest more and juveniles play more than other classes. Juveniles and adult females without infants look for arthropods more often than adult males and females with young infants, who showed the highest frequencies of fruit feeding. Dominant adult males were not consistently the most efficient foragers on fruits according to two different indexes. Most of these results are consistent with the expectations from strong intra-group competition for resources. However, females with infants received benefits during feeding similar to those of dominant adult males, which may be mediated by differential aggression from males to other group members (juveniles and females without infants).     

Location-restricted dyadic interactions and maternal patterns

The purpose of this study was to determine the impact of infant restraint on dyadic interactions and maternal foraging patterns. Five bonnet macaque (Macaca radiata) mother-infant dyads were observed under three conditions: high foraging demand for the mothers with nonrestrained contact between mothers and infants (HFD-NRC), high foraging demand with restrained contact (HFD-RC), and low foraging demand with restrained contact (LFD-RC). In the restrained contact conditions the infants lived in a nursery within the group pen that allowed dyadic nursing, contact, proximity, and grooming, but prevented the infants from being with their mothers in the remaining portions of the pen, including the foraging area. Observations began when the infants were a mean of 5.4 months old. HFD-RC resulted in decreased dyadic contact relative to HFD-NRC, but did not significantly affect foraging task engagement; there were, however, marked individual differences in the response patterns of the mothers. Dyadic contact was also decreased during the LFD-RC condition, but maternal patterns under low demand resulted in lower levels of infant contact initiation. This study demonstrated the feasibility of a nursery-restrained rearing paradigm in exploring the strategic patterns of coping with conflicting environmental and maternal demands in bonnet macaque mothers. © 1993 Wiley-Liss, Inc.     

A comparison of buttress drumming by male chimpanzees from two populations

Wild chimpanzees (Pan troglodytes) produce low-frequency sounds by hitting the buttresses and/or trunks of trees. This buttress drumming occurs in discrete bouts that may be integrated into the phrase sequence of the chimpanzees long-distance vocalization, the pant hoot. The aim of this study was to investigate whether regional variation exists in the drumming behavior of male chimpanzees from Kibale National Park (Kanyawara community), Uganda, and Taï National Park, Ivory Coast. Recordings were made during a 6-month field season at Taï in 1990, and a 12-month field season at Kanyawara in 1996–1997. Acoustic analysis revealed the following: (1) Kanyawara males drummed significantly less frequently in conjunction with a pant hoot or hoot than did Taï males; (2) drumming bouts by Kanyawara males included significantly fewer beats, and were significantly shorter in duration, than those of Taï males; these differences disappeared when only those bouts produced in conjunction with a call were compared; (3) when Kanyawara chimpanzees did call and drum together, they tended to integrate drumming into the vocalization at a later point than did Taï males; and (4) individual differences in the temporal patterning of drumming bouts were not apparent for Kanyawara males, whereas a previous analysis revealed individual differences among Taï males.     

Feeding and ranging patterns of forest hanuman langurs (Presbytis entellus)

The feeding and ranging patterns of a troop of hanuman langurs (Presbytis entellus, Colobinae) were studied in Kanha Tiger Reserve, central Indian Highlands for 1850 hr (1981–1982), in a mosaic of moist deciduous forest and anthropogenic meadow. The location, size, and species of each tree within the 74.5-ha troop annual range was known and the phenology of all tree species was sampled. According to scan sampling, the troop spent 25.7% of the daytime feeding, with range use concentrated on an island of dry deciduous forest. Whereas adjacent troops occupied only the periphery of the focal troop's range, all-male bands occupied its center, especially during takeover and infanticidal attacks. The troop consumed items from 60 of the 67 species of trees and woody climbers available; mature leaves (34.9% of feeding time), fruits (24.4%), leaf buds (10.6%), flowers and flower buds (9.5%), young leaves (3.6%), insects (3.0%), and gum (1%). The monthly utilization of fruit, open leaf buds, and flower buds is correlated significantly with their abundance, and the troop spent significantly more time feeding and less time moving when consuming mature leaves. Comparison of tree dispersion and langur ranging patterns suggests that the distribution of the most important food trees is a major influence on their range use.     

Gene diversity patterns at 10 X-chromosomal loci in humans and chimpanzees

We have investigated the pattern and extent of nucleotide diversityin 10 X-chromosomal genes where mutations are known to causemental retardation in humans. For each gene, we sequenced theentire coding region from cDNA in humans, chimpanzees, and orangutans,as well as about 3 kb of genomic DNA in 20 humans sampled worldwideand in 10 chimpanzees representing two "subspecies." Overallnucleotide diversity in these genes is about twofold lower inhumans than in chimpanzees, and nucleotide diversity withinand between species is low, suggesting that a high level offunctional constraint acts on these genes. Strikingly, we findthat a summary of the allele frequency spectrum is significantlycorrelated in humans and chimpanzees, perhaps reflecting verysimilar levels of constraint at these genes in the two species.A possible exception is FMR2, which shows a higher number ofnonsynonymous than synonymous substitutions on the human lineage,suggesting the action of positive selection.     

Adolescent male chimpanzees do not form a dominance hierarchy with their peers

Dominance hierarchies are a prominent feature of the lives of many primate species. These hierarchies have important fitness consequences, as high rank is often positively correlated with reproduction. Although adult male chimpanzees strive for status to gain fitness benefits, the development of dominance relationships is not well understood. While two prior studies found that adolescent males do not display dominance relationships with peers, additional research at Ngogo in Kibale National Park, Uganda, indicates that adolescents there form a linear dominance hierarchy. These conflicting findings could reflect different patterns of rank acquisition across sites. An alternate possibility arises from a recent re-evaluation of age estimates at Ngogo and suggests that the report describing decided dominance relationships between adolescent males may have been due to the accidental inclusion of young adult males in the sample. To investigate these issues, we conducted a study of 23 adolescent male chimpanzees of known age during 12 months at Ngogo. Adolescent male chimpanzees exchanged pant grunts, a formal signal of submission, only 21 times. Recipients of pant grunts were late adolescent males, ranging between 14 and 16 years old. In contrast, younger adolescent males never received pant grunts from other males. Aggression between adolescent males was also rare. Analysis of pant grunts and aggressive interactions did not produce a linear dominance hierarchy among adolescent males. These data indicate that adolescent male chimpanzees do not form decided dominance relationships with their peers and are consistent with the hypothesis that the hierarchy described previously at Ngogo resulted from inaccurate age estimates of male chimpanzees. Because dominance relationships develop before adulthood in other primates, our finding that adolescent male chimpanzees do not do so is surprising. We offer possible explanations for why this is the case and suggest future studies that may help clarify the matter.