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Many arboreal primates descend to the ground, a custom that may occur more frequently in disturbed habitats, and in the presence of researchers to whom the primates are habituated. In this paper, we describe opportunistic observations of ground use in two groups of northern muriquis (Brachyteles hypoxanthus) at the RPPN Feliciano Miguel Abdala, Minas Gerais, Brazil. Members of both groups were observed drinking, resting, feeding, playing, and traveling on the ground to different degrees, and variation in the levels of habituation of the two groups may be responsible for the differences in the distribution of their terrestrial activities. The potential increase in vulnerability to predation or disease owing to ground use has implications for the conservation of this critically endangered species. Am. J. Primatol. 69:706–712, 2007. © 2007 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]

We monitored the birth patterns of sympatric brown howler monkeys (Alouatta fusca clamitans ) and northern muriquis (Brachyteles arachnoides hypoxanthus ) during a 4-yr period from October 1996 to August 2000 at the Estação Biológica de Caratinga, Minas Gerais, Brazil. Brown howler monkey births (n = 34) occurred throughout the year, and birth frequencies did not differ between rainy and dry season months. The aseasonal birth patterns of the howler monkeys differed significantly from the dry season concentration and dry month peak in muriqui births (n = 23). We found no effects of infant sex or the number of females on interbirth intervals (IBIs) in our 10 howler monkey study troops. IBIs of brown howler monkeys averaged 21.2 ± 2.5 mo (n = 8, median = 21.0 mo), and were significantly shorter following dry season births than rainy season births. Their IBIs and yearling survivorship (74%) were similar to those reported for other species of howler monkeys, but yearling survivorship was much lower than that of muriquis (94%), whose IBIs were more than 12 mo longer than those of the howler monkeys. Our study extends comparative knowledge of birth patterns in Alouatta to a poorly known species, and provides insights into the different ways in which diet and life history may affect the timing of births in large-bodied platyrrhines under the same seasonal ecological conditions. Am. J. Primatol. 55:87–100, 2001. © 2001 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

Fecal samples were collected systematically during a 6-week period, from 13 September-24 October, 1990, from four nonlactating female muriquis (Brachyteles arachnoides) inhabiting an 800 ha forest at Fazenda Montes Claros in Minas Gerais, Brazil. All four females were experienced mothers; one had most recently given birth in June 1988; the other three had most recently given birth in August 1988. Fecal assays measuring progesterone, estradiol, and estrone indicated consistently low levels in the one female who had given birth in June 1988 and in two of the three females who had given birth in August 1988. Elevated steroid levels did, however, appear in fecal samples from the fourth female on day 15 of the collection period. Steroid levels subsequently dropped and then began to rise again during what appeared to be a second cycle. The cycling female was the only one of the four females examined observed to copulate during the collection period. These preliminary data indicate that nonlactating female muriquis do not cycle year-round, resumption of cycling is not tightly synchronized among females even when their prior parturitions were tightly synchronized, and resumed sexual activity appears to be associated with resumed cycling. [ABSTRACT FROM AUTHOR]

Data on feeding behavior in one group of muriquis (Brachyteles arachnoides) were collected during a 14 month study at Fazenda Montes Claros, Minas Gerais, Brazil. Muriquis devoted an average of 51% of their annual feeding time to leaves, 32% to fruits, and 11% to flowers. The high proportion of leaves in their diet is consistent with predictions from the energetics of body size. However, they devoted a greater proportion of their feeding time to patchy fruit and flower resources than was expected from comparisons with smaller, sympatric howler monkeys. Muriqui diet varied with the availability of preferred food types across sample months. Fruit and flower consumption corresponded to the availability and abundance of these food resources in the forest. Leaves contributed substantially to muriqui diet throughout the year but appeared to be eaten primarily to provide necessary protein and/or necessary bulk. Male and female diets differed only in the greater proportion of feeding time females devoted to flowers. [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]

Urine, feces, and copulation frequency were collected from two captive muriqui females, Brachyteles arachnoides , at the Centro de Primatologia do Rio de Janeiro following the resumption of postpartum ovarian cycles. Fecal steroid profiles from seven wild muriqui females at the Estação Biologica de Caratinga, Minas Gerais, Brazil, were compared to the captive females to determine the approximate patterns of steroid excretion relative to the urinary LH peak. Hormonal profiles from one of the captive female muriquis revealed a discrete urinary LH peak. For this female, fecal progesterone increased on the same day as the urinary LH peak, while fecal estradiol increased 6 days later and urinary steroids increased 5 days later. For both captive females, the onset of fecal progesterone increase was preceded by the onset of copulations, which occurred during at least a 5-day period. The complete fecal hormonal profiles of the one captive female for which continuous data were available were similar to those found in wild muriqui monkeys, with the onset of an increase in sustained progesterone levels occurring several days prior to the onset of sustained estradiol increase. These patterns suggest that fecal progesterone may be excreted rapidly in this species. The onset of sustained increase in fecal progesterone levels, together with the consistent delay in the onset of the sustained increase in estradiol, may provide the best indicators of the periovulatory period for muriqui females. Am. J. Primatol. 42:311–321, 1997. © 1997 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]