Birth-related behaviors in wild proboscis monkeys (Nasalis larvatus)

Two births of wild proboscis monkeys took place during a 1991/1992 field study at Tanjung Puting National Park, Indonesia. After conception, both females continued copulating with their group’s male. One of the births took place during the night, the other during mid-morning. In the latter case, the infant was born unassisted while the members of the group watched the birthing process. After parturition, the mother consumed the placenta.     

Ranging Behavior of Proboscis Monkeys (Nasalis larvatus) in the Lower Kinabatangan, Northern Borneo

I studied the ranging behavior of proboscis monkeys (Nasalis larvatus) at two sites in the Lower Kinabatangan Region of northern Borneo. I collected data on ranging behavior via scan sampling during group follows. Groups of Nasalis larvatus had ranges overlapping those of other groups in each area. I observed no territorial behavior. Groups of Nasalis larvatus occasionally swam across the Kinabatangan River, and frequently across its tributaries. The home range size of a focal one-male group (SU1) was 220.5 ha. The group traveled farther on days when the proportion of young leaves in the diet was higher. In addition, SU1 used particular areas when they fed on flowers and fruits. Apparently, rainfall and phenology did not influence ranging patterns.     

Female transfer between one-male groups of proboscis monkey (<Emphasis Type="Italic">Nasalis larvatus</Emphasis>)

Successful or unsuccessful female transfers were observed seven times during a 32-month field study of proboscis monkeys (Nasalis larvatus) inhabiting a riverine forest along a tributary of the Kinabatangan River, Sabah, Malaysia. In all cases, the females voluntarily left their own groups and immediately joined with another one. When adult females tried to shift to other groups, adult males called them back to their own groups, but appeared to be indifferent to subadult females. When the adult females returned, the males never attacked the females physically, but instead often emitted herding sounds to them. One subadult female was repelled by a resident adult female. When one adult female transferred into a new one-male group, she left her behind son in an all-male group. The number of females often fluctuated in most study groups, with this fluctuation being more prominent among subadult females than adult females. It is likely that female transfer in proboscis monkeys is not a rare occurrence and that it is especially common among sub-adult females.     

Feeding ecology of the proboscis monkey (Nasalis larvatus)

Proboscis monkey (Nasalis larvatus) feeding behavior and ecology were studied at the Natai Lengkuas Station, Tanjung Puting National Park, Kalimantan Tengah, Indonesia. Data on feeding behavior were collected using scan sampling during group follows. Three vegetational plots containing 1,732 trees were established and monitored monthly for changes in fruit, flower, and young leaf production. Basal area and canopy cover were calculated and used in estimating food abundance. Proboscis monkeys were found to be folivore/frugivores, specializing in seed consumption. At least 55 different plant species were used as food sources, with a marked preference for Eugenia sp. 3/4,Ganua motleyana and Lophopetalum javanicum. These tree species were among the most frequent and most dominant. However, proboscis monkeys were selective feeders; use of tree species as food sources was not based simply on relative density. During times of low food abundance and/or availability proboscis monkeys switched dietary strategies and increased dietary diversity. The average total home range was estimated to be 130.3 ha, with an average group density of 5.2 groups per km². The average biomass per km² was estimated to be 499.5 kg. Given their high biomass and predilection for consuming seeds of dominant species, proboscis monkeys may help to maintain and increase vegetational diversity.     

Feed intake,digestion and passage of the proboscis monkey (Nasalis larvatus) in captivity

Feeding trials were conducted with a troop of six proboscis monkeys (Nasalis larvatus) at the New York Zoological Park to quantify aspects of digestive physiology. Diets consumed comprised, on an as-fed basis, 55% browse and green produce, 11% fruit, 9% commercial primate diets, 9% root vegetables, and 16% miscellaneous items. Total feed intake averaged 12% of body mass; dry matter intake was 3%. Dry matter and plant cell wall disappearance exceeded 80%. Passage marker studies (three 6-day trials) revealed: transit time=14 hr; mean passage time=49 hr; and 5–80% retention time=52 hr. Digestion coefficients and retention times were greater than expected based on body size. These results might reflect the low fiber content of the diets fed, or alternatively, provide evidence that proboscis monkeys are efficient digesters of cell wall constituents.     

Berliner Nasenaffen - Nachlese

The keeping of Proboscis monkeys in Berlin Zoo starts 1967, the first breeding took place 1971. The highest longevity of a Proboscis monkey born in Berlin Zoo was 17 years and 3 months, the longest time in keeping of an imported animal was nearly 16 years.     

Does intraspecific variation in social systems explain reported differences in the social structure of the proboscis monkey (Nasalis larvatus)?

The social structure of proboscis monkeys (Nasalis larvatus) was investigated in the Brunei Bay area of Brunei Darussalam (Northern Borneo). Intraspecific variability in social systems had been suggested to occur in this species, with social structure varying with habitat differences. Prior reports for this area suggested that groups contained several males, females, and offspring and were unstable. Contrary to these reports, I found that the monkeys were organized into groups containing one male, several females, and offspring. These groups associated at sleeping sites at the river’s edge, thus forming a secondary level of organization. This is the same social system reported in Sarawak, Malaysia and Kalimantan, Indonesia in different habitat types. It appears that methodological differences may account for the discrepancies between reports. I have found no evidence to suggest that intraspecific variation in social systems occurs in this species.     

Selection of river crossing location and sleeping site by proboscis monkeys (Nasalis larvatus) in Sabah, Malaysia

From May 2005-2006, selections of river crossing locations and sleeping sites used by a one-male group (BE-Group) of proboscis monkeys (Nasalis larvatus) were investigated along the Menanggul River, tributary of the Kinabatangan River, Sabah, Malaysia. The frequency of river crossings for focal monkeys in the BE-Group was significantly higher at locations with narrow branch-to-bank distances. Branch-to-bank distances were defined as the distances between the longest tree branches extending over the river and the bank of river on each side. This was measured in areas crossed by the monkeys. The focal monkeys used locations with a higher probability of successful river crossings that did not require jumping into the water and swimming across than those that did. The frequency of sleeping site usage by the BE-Group was positively correlated with the frequency of using river crossing locations by the focal monkeys. Previous reports on predation of proboscis monkeys indicate that clouded leopards (Neofelis diardi) and crocodilians (Tomistoma schlegeli and Crocodylus porosus) may be the major terrestrial and aquatic predators of these monkeys. The selection of river crossing locations by proboscis monkeys may be influenced both by the threat of these predators and the location of suitable and protected sleeping sites. Finally, sleeping sites locations that offer arboreal escape routes may protect proboscis monkeys from leopard attack.     

Social organization and ecology of proboscis monkeys (Nasalis larvatus) in mixed coastal forest in Sarawak

Data are presented from a 16-month study of proboscis monkeys in an area of mixed coastal forest in Sarawak. The population density, social organization, and feeding and ranging behavior are described in detail. Results are compared with those from other primates in an attempt to understand why females of certain species (including proboscis monkeys) transfer between social groups. The scarcity of available food and reasons for the limited habitat preferences of proboscis monkeys are also discussed.     

Males of the orb-web spider Argiope bruennichi sacrifice themselves to unrelated females

Costs of inbreeding can lead to total reproductive failure and inbreeding avoidance is, therefore, common. In classical sex roles with no paternal care, the selective pressure to avoid inbreeding is mostly on the female, which carries the higher costs. In some orb-web spiders, this situation is very different because females are polyandrous and males are monogynous or at most bigynous. Additionally, females of many entelegyne orb weavers are thought to bias paternity post-copulatorily towards a desired mate. This increases the selective pressure on males to adjust their investment in a mating with regard to the compatibility to a female.Here, we examine whether genetic relatedness influences mating behaviour in the orb-web spider Argiope bruennichi. We mated either a sibling or a non-sibling male to a female in single copulation trials and compared copulation duration, cannibalism rate and female fecundity.Our experiment revealed that males prolonged their copulation duration and were cannibalized more frequently when mating with a non-sibling female. Males mating with a sibling female were more likely to escape cannibalism by copulating briefly, thus presumably increasing their chances of re-mating with a more compatible female. This suggests that males can adaptively adjust their investment relating to the compatibility of a female.     

Group Fission in Barbary Macaques (Macaca sylvanus) at Affenberg Salem

We analyzed eight group fissions occurring during a 20-year period in three groups of a free-ranging provisioned Barbary macaque population. The founder group fissioned four times within 3.5 years after transfer to the enclosure, indicating that external factors—new environment, more space, absence of other groups—facilitated group fissions. Two groups resulting from these fissions, split twice within 2.5 and 1 years, respectively, many years later. The process of fissioning lasted from a few months to almost 2 years. Fissions were preceded by peripheralization/subgrouping of mainly young adult males (8-10 years old), suggesting that male competition was the primary force for the fissions. The males were joined by middle- to low-ranking but not the lowest-ranking females. The resulting new groups were usually smaller than the groups in which the former -matriline—old groups—stayed, and they were also more variable in size and sex ratio, suggesting that variable numbers of surplus individuals were expelled during fission. Mean adult sex ratios were similar in both groups after fission, indicating that the competitively superior males in the old groups (groups + -matriline) could not increase their breeding opportunities. Female kin, even of large matrilinies, almost always stayed together during fission. Natal males strongly preferred to join the old groups, and this preference was most pronounced in juveniles and subadults. Hence, most natal males stayed with maternally related females, i.e., remained true natal males, if the females stayed in old groups. They were separated from female kin, i.e., became seminatal, if the females joined the new groups. These seminatal males did not differ from natal males with respect to matrilineal rank, but they had more female relatives, above all more close relatives (sisters), indicating that avoidance of mating with maternal kin was important for group choice. Despite joining the same group as female kin during fissioning, breeding opportunities of natal males (ratio of unrelated females/male) were not less than that of their seminatal peers, because natal males had fewer female relatives. Only a minority of both groups of males would have done better by joining the alternative group. Paternal relatives were distributed during fission by chance, and loss of patrilinies was therefore much less pronounced. We conclude that the rules governing social relationships among Barbary macaque males are less apt to cope with the high number of males resulting from provisioning, whereas the rules regulating social relationships of females living in a nepotistic, female-bonded society are very robust in this respect.     

Male Migration in Barbary Macaques (Macaca sylvanus) at Affenberg Salem

We analyzed male migration during a 20-year period in the free-ranging Barbary macaque population of Affenberg Salem. Most natal migrations occurred around puberty, but only one third of all males left the natal group. Secondary group transfers were rare. All males immediately transferred to other bisexual groups. Migration rates were highest during periods with high adult female/male ratios within social groups. Immigrants highly preferred groups with fewer males of their own age than in the natal group, and many males immigrated into groups that had no male their own age. These groups originated from a skewed distribution of resident males during group fissions. A comparison of emigrants with their natal peers supports the inbreeding avoidance hypothesis as cause of emigration rather than the male competition avoidance hypothesis. Emigrants had no lower individual rank position and did not come from lower-ranking matrilines. Emigrants had more female maternal relatives, especially sisters. Males without female relatives almost never emigrated. Conversely, there is virtually no indication that emigrants were evicted from the natal group. Emigrants had no increased mortality. Paternity data revealed that the reproductive success of emigrants and natal males is similar, indicating that emigration had no reproductive cost. Many similarities between emigrants and natal males that separated from female maternal kin during group fissions suggest that inner migration during fissions is an alternative way to avoid maternal inbreeding. The mating system resulted in a genetic structure within social groups that largely diminished the chances for paternal inbreeding even without recognizing paternal kin.     

Social Relationships Among Male <Emphasis Type="Italic">Alouatta pigra</Emphasis>

We investigated male social relationships in 2 groups of black howlers (Alouatta pigra) in Palenque National Park, Mexico, over a 14-mo study characterized by frequent changes in male group membership. Both single males and pairs of males entered our focal groups. Single males tended to join groups, whereas pairs of males entering groups together successfully evicted resident males. The 19 male dyads across the 11 periods defined by changes in group membership were rarely in close proximity or interacting with one another. Nevertheless, 1 male formed significantly closer associations with resident females in 6 periods and achieved higher mating success during 4 of the periods when ≥1 female was sexually active. In the other 5 periods, no particular male maintained significantly closer associations with resident females, which may be a result of the rapid sequence of changes in male membership and corresponding social instability. Resident males participated frequently and consistently in mutual howling, but the resident male with the strongest female associations and highest mating success initiated howling bouts more frequently in all but 1 of the 6 socially stable periods. Though still preliminary, our findings suggest that variation in social relationships among male black howlers may be more related to their ability to establish strong relationships with females than to their relationships with one another.     

Bird predation by captive woolly monkeys (Lagothrix lagotricha)

Vertebrate predation has not been reported for woolly monkeys (Lagothrix lagotricha) in their natural habitat. However, bird predation has been observed in captivity. The present report is based on 15 incidents of bird predation that occurred during a 1-year observational study of the nine woolly monkeys at the Louisville Zoo. All identified captures were by females. The captor and her prey were frequently pursued by the other monkeys. Social rank was related to attempts to steal the prey. Consumption was characterized by much chewing and frequent alternation between the prey and highly fiberous substances. Predation was not characterized by stereotypical behaviors for pursuit or killing of prey, but instead suggested opportunistic capture by a generalized organism. The low frequency of bird predation by captive woolly monkeys may indicate that a similar level of predation has gone undetected in the study ofLagothrix in the wild.     

The nomenclature and taxonomy of the colobine monkeys of Java

The current terminology for the colobine monkeys of Java is incorrect. The appropriate term for the West Javan surili is Presbytis comataDesmarest,1822, and that for the Javan and Bali/Lombok lutung is Trachypithecus auratusE. Geoffroy St. Hilaire, 1812.     

Sex-biased dispersal in eastern chipmunks, Tamias striatus

I investigated the effect of male mate competition and inbreeding avoidance on natal dispersal of chipmunks by longitudinally monitoring known individuals from 1986 to 1990. Natal males exhibited greater absolute and effective dispersal distances but dispersed at the same proportion as natal females. Recruitment of juvenile males was negatively affected by density of resident males, but there was no evidence of local mate competition among male kin. Analysis of the spatial distribution of neighbors showed that natal males settled farther from their mothers than did their female siblings and farther than unrelated juvenile males. In addition, mothers apparently tolerated daughters as close neighbors and occasionally shared den sites with grandprogeny. Sexually mature males were never neighbors of their mothers and were never observed at maternal mating bouts. Males may disperse to improve reproductive opportunities by avoiding competition with resident males, and by increasing access to unrelated females. Maternal tolerance of daughters but not sons may result in the close affiliation between mothers and daughters, and indirectly contribute to dispersal of natal males. Hence male-biased dispersal could be a consequence of mate competition and maternal avoidance of incestuous matings. This revised version was published online in July 2006 with corrections to the Cover Date.