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Habitat fragmentation due to human activities is one of the principal threats to all primates and is particularly so for arboreal platyrrhines. Its impact has been extreme in the Brazilian Atlantic forest, where most primate populations have been severely reduced in numbers and their distributions restricted, resulting in low probabilities of long-term persistence. One of the most severely affected species is the northern muriqui (Brachyteles hypoxanthus), which today has fewer than 1,000 individuals distributed over only a dozen populations and is considered to be Critically Endangered. Most of these populations are isolated and smaller than 50 individuals, including the population inhabiting the Sossego Forest in Simonésia, Minas Gerais. With fewer than 30 individuals associating in one social group, the Sossego muriqui population is doomed to extinction unless emergency management measures are implemented to protect it. We monitored the demography of the Sossego muriquis to evaluate the impacts of the introduction of a reproductive-aged female that was translocated into this population in December 2006. Data were collected on all individuals, identifiable from their natural markings, during 3 to 12 monthly surveys conducted each year from July 2012 to June 2020. They revealed that the population grew from 32 individuals in July 2012 to a peak of 38 in September 2015, but then declined to a low of 22 individuals in September 2017, coinciding with a yellow fever outbreak in the region. As of June 2020, there were 24 individuals present. Four of the surviving individuals were the translocated female and three of her five offspring. One of her daughters was confirmed to have emigrated to another forest fragment and a second daughter has not been seen since March 2019 and is suspected to have emigrated. During the eight years of monitoring, we recorded 17 births (11 females and six males) and 25 disappearances involving 17 females, including the female confirmed to have dispersed, and eight males. Our results emphasize the risks of demographic stochasticity in small, isolated populations. The confirmed emigration of one dispersal-aged female that failed to locate a group to join, and the absence of any immigrants, call attention to the demographic implications of translocation as a potential conservation tool for small, isolated populations of species such as the northern muriqui in which female dispersal and male philopatry are typical. [ABSTRACT FROM AUTHOR]

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]