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Although well documented in matrilocal primate species, group fission is still a poorly known phenomenon among patrilocal primates. In this paper we describe in detail a group fission event in the population of northern muriquis at the Reserva Particular do Patrimônio Natural-Feliciano Miguel Abdala in Caratinga, Minas Gerais, Brazil, using Social Network Analyses (SNA). Data on association patterns were collected during systematic observations from May 2002 to September 2005, and analyzed for dry (from May to October) and rainy seasons (from November to April). The fission process started with subgroup formation in the rainy season 2002-2003, and was completed by the dry season of 2003. By the dry season 2003, the parent group (Jaó) had fissioned to form a second mixed-sex group (Nadir) while a subgroup of males (MU) moved between the parent group and the newly established group. Before the Jaó group fission started (dry season 2002) and during its initial phases (rainy season 2002-2003), females that ultimately composed the daughter group (Nadir) were the most peripheral in the association network. In the rainy season 2002-2003, the median monthly ( N = 6) operational sex ratio (OSR) of Jaó group was 2.81. However, once Jaó females initiated the fissioning process to establish the Nadir group, the OSR was more favorable to males in the Nadir group than in the Jaó group. Our results suggest that males followed the females to escape an unfavorable OSR in their natal group. Am. J. Primatol. 76:529-538, 2014. © 2013 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Increased body size in B rachyteles has been regarded as an important evolutionary adaptation that allowed a greater reliance on leaves compared to other more frugivorous Atelidae, but its association with muriqui positional behavior and substrate use is still unknown. Here, we present original data on the feeding and resting postures of the northern muriqui ( B rachyteles hypoxanthus) and evaluate predictions about the relationships between body size, postural behavior, and substrate use derived from previously published data for other atelids (e.g. A louatta, A teles, and L agothrix). The study was undertaken from August 2002 to July 2003 on a large group of well-habituated muriquis inhabiting the Reserva Particular do Patrimônio Natural - Felíciano Miguel Abdala in Minas Gerais, Brazil. Consistent with our predictions, we found that B . hypoxanthus was highly suspensory during postural feeding (60.9%) and commonly used tail-hind limb suspension/horizontal tripod (38.0%) or tail-forelimb/hind limb suspension (21.4%). However, although tail-suspensory postures permitted the muriquis to use the terminal canopy and small-sized substrates, these areas were also accessed via tail-assisted above-branch postural behaviors involving multiple substrates. Unexpectedly, tail-suspensory postures were found to be frequently associated with large substrates, tree trunks, and the understory. We suggest that B rachyteles' ability to access food resources from all areas of a feeding tree and from tree crowns at different canopy levels may account for their ability to efficiently exploit food resources in seasonal disturbed forest fragments of the Brazilian Atlantic Forest today. Am. J. Primatol. 75:74-87, 2013. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

We present data on the spread of terrestrial activities in one group of wild northern muriqui monkeys (Brachyteles hypoxanthus). Both males and females consumed fruit, drank, rested, traveled, and socialized terrestrially, but proportionately more males spent significantly more of their time on the ground than females, and females were more likely to engage in terrestrial activities when accompanied by males than when by themselves. Terrestrial activities occurred in both open and closed habitats where arboreal substrates were available and utilized by other individuals engaged in similar activities. Ecological and demographic factors may have stimulated the muriquis’ vertical niche expansion, but increases in the frequency and diversity of terrestrial activities, the high proportion of group members that engage in terrestriality, and its diffusion along male-biased social bonds are consistent with the development of a local terrestrial tradition similar to other types of traditions described in other primates. [Key words: terrestriality, ecology, predation, tradition] [ABSTRACT FROM AUTHOR]

Female northern muriquis (Brachyteles hypoxanthus) are known to engage in frequent copulations with multiple partners, a pattern that in other primates has been attributed to various functions such as confusing paternity, reducing male aggression, or ensuring fertilization. However, in some female primates, promiscuity is restricted to times when conceptions are unlikely. We investigated whether female northern muriquis might exhibit a similarly mixed strategy by examining their mating, social, and activity patterns during their conception cycles versus other times. Systematic behavioral data were collected during an 18-month period between August 2001 and February 2003 on 13 adult females in a well-studied group at the RPPN-Feliciano Miguel Abdala, Minas Gerais, Brazil. Females mated on an average of 12.5±7.9 days during the study period, and spent significantly less time resting and engaging in non-sexual social behaviors, and significantly more time in sexual behaviors on days that they copulated than on days they did not. Three of the eight females for which sufficient data were available copulated significantly more often with their spatially closest non-kin associates, and four of five females that could be analyzed copulated significantly more often with their most frequent non-kin embrace partners. Comparisons between conception and non-conception periods revealed no differences in female activity budgets or in either the number of copulations or the number of different mating partners per female. Our results suggest that some females mate preferentially with close associates and social partners, but there is no indication that females alter their behavior during the cycles in which they conceive. Am. J. Primatol. 69:766–776, 2007. © 2007 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

The 957-ha forest at the Estação Biológica de Caratinga/Reserva Particular do Patrimônio Natural-Felìciano Miguel Abdala, in Minas Gerais, Brazil, supports one of the largest known populations of the critically endangered northern muriqui (Brachyteles hypoxanthus). We combine long-term data on one group that has been monitored since 1982 with new data obtained on the other three groups since 2002 and 2003 to describe the demographic structure of this population, evaluate its potential for future growth, and predict how dispersal and competitive regimes may change in response to current demographic conditions. As of January 2005, the 226 individuals in the population were divided into four mixed-sex groups with 37-77 members, and an all-male unit whose eight males maintained transient associations with two of the mixed-sex groups. Although 51.77% of the population was female, the sex ratio among adults and subadults was female-biased (0.75), while that among immatures was male-biased (1.47). Consistent with expectations from mean interbirth intervals, 64.18% of adult females gave birth in 2003 and 2004. However, by January 2005, only 52.31% of adult females were still carrying infants < 24 months of age due to unusually high infant mortality. First-year survivorship among the 25 infants born in the population in 2003 was only 76%, considerably lower than previously documented in the longest-studied group. High female fecundity is indicative of a healthy population, but the current male bias in births will result in a decline in the population growth rate within two decades, and may increase levels of male reproductive competition and alter dispersal patterns. [ABSTRACT FROM AUTHOR]

We measured fecal androgen (T+DHT) and estradiol (E2) levels in female northern muriquis (Brachyteles hypoxanthus) at the Estação Biológica de Caratinga/RPPN Feliciano Miguel Abdala, Minas Gerais, Brazil, to evaluate the hormonal bases underlying individual variation in the resumption of cycling and conception. We found that androgen levels were significantly lower in females than in males, and that there were no consistent patterns in female androgen levels across precycling or cycling conditions. Females that resumed cycling earlier in the study (weeks 4–8) had higher precycling E2 levels and correspondingly lower precycling androgen/E2 ratios than females that resumed cycling later (weeks 12–16). There were no differences in female precycling androgen levels, but cycling females that conceived during or immediately after the study period had lower androgen levels and threefold higher E2 peaks than the one cycling female that failed to conceive. These results suggest that minimum E2 thresholds are necessary for both the resumption of ovarian cycling and conception. Individual variation in these components of fertility may be regulated by differences in E2 levels, which affect androgen/E2 ratios, rather than by androgen levels per se. Further research into the relative concentrations of T vs. DHT will be necessary to fully evaluate whether androgens affect cycling and conception in this species. Am. J. Primatol. 67:69–81, 2005. © 2005 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

We investigated hormonal and behavioral changes in wild male and female northern muriquis (Brachyteles arachnoides hypoxanthus ) at the Estação Biológica de Caratinga, Minas Gerais, Brazil, during a 6-mo period that encompassed the onset of the 1998–1999 mating and conception seasons. Individual females resumed mating with the resumption of ovarian cycling, which was not synchronized among them or related to their cortisol levels. Females experienced two to seven cycles prior to conceiving, and the first conception occurred 2 mo after the onset of the group's mating season. There were no differences in female cortisol levels across their premating, mating, and conception conditions. Cortisol levels were significantly higher in females than in males prior to the conception season, consistent with the prediction that energy reserves may be associated with breeding readiness in females, but not males, in this species. The sustained elevation in male cortisol occurred after the peak in their sexual activity, which resulted in the first conception of the year. Male cortisol levels were positively correlated between years that were similar in rainfall, but differed in the timing of sexual and reproductive events. The timing of cortisol elevations in males appears to be generally regulated by environmental cues, but is responsive to fine-tuning by social and behavioral cues related to the unpredictable timing of reproductive opportunities within their extended mating season. Am. J. Primatol. 61:85–99, 2003. © 2003 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

One group of woolly spider monkeys, or muriquis (Brachyteles arachnoides), was observed from June 1983 through July 1984 at Fazenda Montes Claros, Minas Gerais, Brazil. The study subjects spent an average of 49% of their daylight time resting, 29% traveling, and 19% feeding. They shifted their diurnal schedule of activities in response to seasonal changes in temperature and rainfall. The activity budgets of adult males and females were similar. However, a comparison of three adult females in different reproductive conditions revealed that the lactating female spent a greater proportion of time feeding than did both the pregnant and nonreproductive females. Intraspecific differences in group size and diet appear to be important to understanding differences in the activity budgets of Brachyteles. Differences between locomotion patterns of woolly spider monkeys and sympatric howler monkeys may explain activity budget differences based on group size and diet. [ABSTRACT FROM AUTHOR]