Northern muriquis inhabit tropical, semi-deciduous, late successional forests and prefer areas with large trees and high tree density. The dense canopy of the late successional forests increases the ease of movement for the northern muriqui to travel via brachiation. The average canopy height of forests inhabited by northern muriquis is 13.4 m and the average tree density of their habitat is 669.3 trees per hectare. Their habitat has been greatly disturbed by human activity, creating large gaps between habitat patches that have increased the use of ground travel to move between patches. The maximum elevation northern muriquis occupy is 681.7 m above sea level. (Arnedo, et al., 2010; Boubli, et al., 2010; Boubli, et al., 2011; Mourthe, et al., 2007; da Silva Junior, et al., 2009)
Northern muriquis resemble the closely related southern muriquis (Brachyteles arachnoides), which are large primates characterized by long extremities, a long prehensile tail, and a large, round belly. The long prehensile tail of northern muriquis are important for arboreal travel and feeding. The long arms of northern muriquis are also important for travel. Their fur is thick with a light brown to gold coloring. There is slight sexual dimorphism in northern muriquis. Morphometric data on northern muriquis has not been measured, but we can assume that they are similar to those of southern muriquis, that can weigh from 6.9 to 15 kg, with an average female body mass of 8.4 kg and an average male body mass of 9.6 kg (Aguirre 1971 as cited in Cunha et al. 2005). Body length of northern muriquis is also similar to southern muriquis, whose body can range from 46.1 to 49.7 cm in length, with a tail length of 72.6 to 81.0 cm. The average southern muriqui female tail length is 78.0 cm, which exceeds the average body length of 48.6 cm. This is also the case for male southern muriquis, whose average tail length is 74.0 cm and average body length is 49.0 cm. The length of the tail typically exceeds that of the body. The testes size of northern muriquis has not been described, but is likely similar to that of southern muriquis, with an average total testes volume of 952.4 cm^3. The dental characteristics of northern muriquis have not been described, but southern muriquis have a dental formula of 2/2 + 1/1 + 4/4 + 3/3 for a total of 40 teeth.
Northern muriquis closely resemble southern muriquis, but a few morphological features are distinct. The face of northern muriquis is mottled black and pink, while the face of southern muriquis is entirely black. The scrotum of male northern muriquis is also black and pink while in southern muriquis it is black. Another morphological difference between the two species is the presence of a rudimentary thumb in northern muriquis, ranging from 0.3 to 1.9 cm, and the lack of a thumb in southern muriquis. Finally, canine lengths do not differ between the sexes in northern muriquis, while male southern muriquis have significantly longer canines than females. In addition to physical distinctions, there are high levels of genetic divergence and reproductive isolation between northern and southern muriqui populations. The overall fixation index (Fst) of 0.413 indicates low gene flow and high differentiation between the two populations. (Cunha, et al., 2005; Di Fiore and Campbell, 2007; Eisenberg and Redford, 1999; Emmons and Feer, 1990; Iurck, et al., 2013; Lemos de Sa and Glander, 1993; Lemos de Sa, et al., 1991; Lemos de Sa, et al., 1993; Milton, 1984; Strier, 1986; Zingeser, 1973)
Male and female northern muriquis have a promiscuous mating system, with both sexes mating with multiple partners. Northern muriquis also have an egalitarian society, where there are no dominant or subordinate individuals. As a result, male muriquis most likely compete via sperm competition as they have very large testes. Male southern muriquis have previously been observed to consume their excess ejaculate, possibly due to its’ high protein content, a behavior which northern muriquis may also employ. (Possamai, et al., 2007; Strier, 1986; Strier, et al., 2002)
There is little information available on the reproduction of northern muriquis, though we can assume that information on southern muriqui reproduction is relevant due to their similar habitat and morphology. In southern muriquis, sexual receptivity of the female is communicated to the male via pheromonal cues in the urine. Females urinate and spread the urine on their hands in order to create a pheromonal trail for male muriquis while they travel. Prior to copulation, a male southern muriqui will smell the genitals or taste the genital secretions of the female. A male or female may initiate these "inspection" behaviors and these events may or may not be followed by copulation. To avoid the negative effects of inbreeding, northern muriquis avoid mating with closely related individuals. Mother northern muriquis especially avoid mating with their sons. In order to improve their chances of successfully mating, male northern muriquis aggregate in large male groups to attract more females. The age of sexual maturity in female northern muriquis ranges from 5 to 11 years old and the age of sexual maturity in male northern muriquis ranges from 4 to 8 years old. Though sexual maturity can be reached at an earlier age, the typical age of first reproduction for female muriquis is 7 years old. Female muriquis may disperse from their natal social group to reproduce, typically at 5 to 7 years of age. If female northern muriquis do disperse from their natal group, most will do so prior to sexual maturity and sexual maturity may be delayed in these females. The average age of first birth in females that have successfully dispersed is 8.7 years old. (Martins and Strier, 2004; Milton, 1984; Possamai, et al., 2005; Strier and Mendes, 2009; Strier and Mendes, 2012; Strier and Ziegler, 2000; Strier, et al., 2006; Strier, et al., 2011; Strier, 1986; Strier, 1996; Strier, et al., 2002; Tolentino, et al., 2008)
Complete data on the reproductive history of northern muriquis has not been collected, but based on the data available on southern muriquis, they may give birth every three years. Sexually mature northern muriquis of all age classes copulate at similar levels, though there is an increased chance of ejaculation following copulation with increasing age in northern muriquis. Female and male northern muriquis may remain sexually active and reproductive up to the age of 30 years. Following the birth of offspring in northern muriquis, there is a two-year interval in which the mother cares for her offspring prior to restarting the ovarian cycling and copulation. Northern muriquis breed during the rainy season (October to April) of Brazil and give birth during the dry season (May to October). The breeding season is approximately 82 days in length. In southern muriquis, the ovarian cycle can range from 16 to 38 days and they have a relatively long gestation period of 7 months. Northern muriquis have been documented to produce a minimum of one offspring per birth, but the maximum number of offspring capable of being produced has not been documented. (Arnedo, et al., 2010; Dias and Strier, 2003; Martins and Strier, 2004; Possamai, et al., 2005; Strier and Ziegler, 1997; Strier and Ziegler, 2000; Strier and Ziegler, 2005; Strier, et al., 2006; Strier, 1996; Strier, et al., 2003; Strier, et al., 2001; Wiederholt and Post, 2011)
Muriqui offspring are incredibly dependent upon their mother during the first year of life. During the first 3 to 6 months of life the offspring hangs from the belly of its mother to travel. Eventually, at the age of 6 months, the young muriqui moves onto the mother’s back to travel. In addition to carrying them, female muriquis groom their immature offspring. The weaning period has not been described for northern muriquis, but southern muriquis begin to wean their offspring at 14 to 18 months old. During the weaning period, the mother continues to carry her offspring on her back. Female northern muriquis in the process of weaning their young are found in groups with other females. The mother stops carrying her offspring when it has reached the age of 2 years old, at the end of the weaning period. Female northern muriquis do not prefer their male offspring to their female offspring and care for them equally. Infant swapping has previously been observed in northern muriquis, where two females exchanged their offspring for an elongated period of time and the non-mother female nursed and carried the offspring of the other female and vice versa. (Guedes, et al., 2008; Martins, et al., 2007; Milton, 1984; Strier, et al., 2006; Strier, 1993; Tolentino, et al., 2008)
Northern muriquis live until at least the age of 30 years old in the wild. (Possamai, et al., 2005)
Northern muriquis are social primates and live in groups of both males and females, which range from 48 to 81 individuals. These large social groups may be constructed of 13 to 18 males, 18 females, and 20 to 31 juveniles or subadults. Due to their thick, forested habitat, northern muriquis of one group may become visually separated from one another. In these large multi-sex groups, smaller subgroups may separate from the larger group to feed and rest. Male northern muriquis generally spend a greater amount of time in smaller all male groups, which range from 8 to 9 individuals. These small male groups do not demonstrate aggression towards one another and do not physically compete for females. Female northern muriquis spend a greater majority of time alone and away from these male groups and other females, feeding alone or with offspring. During arboreal feeding in tall trees on fruits and leaves, northern muriquis use their tail to support themselves. Female northern muriquis also tend to associate more with other adult females than males when they are not mating. Northern muriquis have an egalitarian society. Agonistic behaviors are very rare in muriquis. When hostile encounters occur between two northern muriqui social groups, many small male groups within the larger social group will work together to defend the females of their social group. When aggressive behaviors occur among individuals within the same social group they are usually not related to competition for resources, but are typically females of the social group chasing new females that have recently dispersed into the group. Northern muriquis are arboreal and diurnal primates. They travel via brachiation throughout the canopy using their long arms and tail. In disturbed habitats, northern muriquis spend more time moving on the ground. Northern muriquis move down to the ground to feed, rest, and socialize. Males also spend more time on the ground than females. Based on data collected on southern muriquis, northern muriquis may engage in play and embracing behaviors. The activity budgets of northern muriquis are also assumed to be similar to those of southern muriquis, where, during the day, as much as half their time is spent inactive and resting and the other half of their day is divided up between feeding, traveling, and socializing. (Arnedo, et al., 2010; Boubli, et al., 2011; Di Fiore and Campbell, 2007; Dias and Strier, 2003; Iurck, et al., 2013; Mendes and Ades, 2004; Milton, 1984; Mourthe, et al., 2007; Strier, et al., 2011; Strier, 1986; Strier, 1992; Strier, et al., 2002; Tabacow, et al., 2009; Tokuda, et al., 2012; Tolentino, et al., 2008)
Northern muriqui home range size has been observed to vary with group size. The estimated home range of a northern muriqui group of 60 individuals is 302 hectares. (Dias and Strier, 2003)
Northern muriquis communicate with each other vocally using a variety of call types and these vocalizations may be used for long and short distance communication. During vocalizations, northern muriquis take turns answering the initial vocalizer, called a sequential exchange. The neighing vocalization of northern muriquis may be used to keep the social group together and inform individuals about group movement (Nishimura et al. 1988 as cited in Arnedo et al. 2010). The staccato vocalizations produced by female northern muriquis could be to ensure sufficient space between themselves and other females during feeding, in order to maximize their energy intake and avoid competition. (Arnedo, et al., 2010; Mendes and Ades, 2004)
Northern muriquis are completely herbivorous and consume a variety of plant foods (Mourthe et al. 2008). Their diet includes leaves, fruits, vines, flowers, bark, nectar, and seeds. Northern muriquis consume the fruits of Margaritaria nobilis, Andira species, Anadenanthera species, Plathymenia foliolosa, Palicourea tetrapylla, Psychotria wamingii, Genipa americana, and Carpotroche brasiliensis as well as the seeds of Mabea fistulifera. Based on data collected on the closely related southern muriqui, northern muriquis may prefer to consume new leaves over mature leaves. Fallen fruit is also frequently consumed. Northern muriquis exhibit geophagy or soil consumption. Individuals of all ages and sexes consume soil and this behavior is thought to supplement their dietary nutrients as high levels of vanadium, aluminum, chromium, iron, nickel, titanium, and zinc were found in the consumed soils. Geophagy may also increase digestion and nutrient absorption efficiency as the acidic soils can change the pH of the stomach. (Dias and Strier, 2003; Dib, et al., 2001; Mourthe, et al., 2007; Mourthe, et al., 2008; Strier, 1986; Strier, 1991; Tabacow, et al., 2009; de Melo, et al., 2005)
The main predator of northern muriquis are ocelots (Leopardus pardalis). Tayras (Eira barbara) prey on southern muriquis, and may also prey on northern muriquis as their range overlaps that of northern muriquis. Jaguars (Panthera onca), pumas (Puma concolor), and feral dogs may also prey on northern muriquis. Humans (Homo sapiens) actively hunt muriquis. (Cunha, et al., 2005; Printes, et al., 1996; Tabacow, et al., 2009; de Cassia Bianchi and Mendes, 2007; de Cassia Bianchi, et al., 2010)
Due to their diet of seeds and fruits, northern muriquis act as important seed dispersers for a variety of Atlantic forest plants. Northern muriquis also support a commensal intestinal parasite, a Strongyloides species. (Dib, et al., 2001; Mourthe, et al., 2008)
No positive impacts of the northern muriquis have been recorded for humans, though they may provide some benefit to the individuals that actively hunt them. (Cunha, et al., 2005)
There are no known adverse impact of northern muriquis on humans.
Northern muriquis are deemed critically endangered by the International Union for the Conservation of Nature and are one of the world’s top 25 most endangered primates. There are approximately 855 to 1000 northern muriquis currently living in the wild. One factor that is negatively affecting their survival is the reduction of their range and habitat. Northern muriquis prefer late successional forest habitat, and forestry and logging are negatively impacting them by removing their preferred habitat. The prevalence of introduced bamboo is also causing problems for muriqui conservation as they do not eat it and it tends to slow forest succession. In order to facilitate the conservation of the northern muriqui, researchers must work towards habitat restoration of late successional forests. Human hunting is also a major threat to northern muriquis survival. In order to sustain a genetically and demographically stable population of at least 700 individuals, northern muriquis would require 11,570 hectares of habitat to persist. Research and conservation programs have been implemented for the northern and southern muriquis in the Brazilian states of Minas Gerais, Espirito Santo, Sao Paulo, and Rio de Janeiro. An important conservation reserve for the northern muriqui is the Reserva Particular do Patrimonio Natural Feliciano Miguel Abdala (Caratinga Biological Station) in Brazil. The area surrounding this biological station supports a northern muriqui population that may have been increasing since 2007. Northern muriquis are also found at the Augusto Ruschi Biological Reserve. (Boubli, et al., 2011; Brito and Grelle, 2006; Costa, et al., 2005; Cunha, et al., 2005; Lemos de Sa, et al., 1991; Mendes, et al., 2005; Mendes, et al., 2008; Mittermeier, et al., 2006; Vieira and Mendes, 2005; da Silva Junior, et al., 2009)
Tera Edkins (author), University of Manitoba, Jane Waterman (editor), University of Manitoba, Tanya Dewey (editor), University of Michigan-Ann Arbor.
living in the southern part of the New World. In other words, Central and South America.
uses sound to communicate
Referring to an animal that lives in trees; tree-climbing.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
uses smells or other chemicals to communicate
humans benefit economically by promoting tourism that focuses on the appreciation of natural areas or animals. Ecotourism implies that there are existing programs that profit from the appreciation of natural areas or animals.
animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.
parental care is carried out by females
an animal that mainly eats leaves.
an animal that mainly eats fruit
an animal that mainly eats seeds
An animal that eats mainly plants or parts of plants.
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
having the capacity to move from one place to another.
the area in which the animal is naturally found, the region in which it is endemic.
generally wanders from place to place, usually within a well-defined range.
the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.
rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.
breeding is confined to a particular season
reproduction that includes combining the genetic contribution of two individuals, a male and a female
associates with others of its species; forms social groups.
uses touch to communicate
Living on the ground.
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
uses sight to communicate
reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.
Arnedo, L., F. Mendes, K. Strier. 2010. Sex differences in vocal patterns in the Northern Muriqui (Brachyteles hypoxanthus). American Journal of Primatology, 72: 122-128.
Boubli, J., F. Couto-Santos, I. Mourthe. 2010. Quantitative assessment of habitat difference between northern and southern muriquis (Primates, Atelidae) in the Brazilian Atlantic forest. Ecotropica, 16: 63-69.
Boubli, J., F. Couto-Santos, K. Strier. 2011. Structure and floristic composition of one of the last forest fragments containing the critically endangered northern muriqui (Brachyteles hypoxanthus, Primates). Ecotropica, 17: 1-17.
Brito, D., C. Grelle. 2006. Estimating minimum area of suitable habitat and viable population size for the northern muriqui (Brachyteles hypoxanthus). Biodiversity and Conservation, 15: 4197-4210.
Chaves, P., C. Alvarenga, C. Possamai, L. Dias, J. Boubli, K. Strier, S. Mendes, V. Fagundes. 2011. Genetic diversity and population history of a critically endangered primate, the northern muriqui (Brachyteles hypoxanthus). PLoS one, 6: 1-12.
Costa, L., Y. Leite, S. Mendes, A. Ditchfield. 2005. Mammal conservation in Brazil. Conservation Biology, 19: 672-679.
Cunha, A., C. Grelle, J. Boubli. 2005. Distribution, population size and conservation of the endemic muriquis (Brachyteles spp.) of the Brazilian Atlantic Forest. Oryx, 43: 254-257.
Di Fiore, A., C. Campbell. 2007. The Atelines: variation in ecology, behavior, and social organization. Pp. 155-185 in C Campbell, A Fuentes, K MacKinnon, S Bearder, R Stumpf, eds. Primates in Perspective. New York: Oxford University Press.
Dias, L., K. Strier. 2003. Effects of group size on ranging patterns in Brachyteles arachnoides hypoxanthus. International Journal of Primatology, 24: 209-221.
Dib, L., A. Oliva, K. Strier. 2001. Geophagy in muriquis (Brachyteles arachnoides hypoxanthus): first reports. Revista de Etologia, 3: 67-73.
Eisenberg, J., K. Redford. 1999. Mammals of the neotropics: the central tropics Volume 3 Ecuador, Peru, Bolivia, Brazil. Chicago: University of Chicago Press.
Emmons, L., F. Feer. 1990. Neotropical rainforest mammals: a field guide. Chicago: University of Chicago Press.
Groves, C. 2001. Primate taxonomy. Washington and London: Smithsonian Institution Press.
Guedes, D., R. Young, K. Strier. 2008. Energetic costs of reproduction in female northern muriquis, Brachyteles hypoxanthus (Primates: Platyrrinhi: Atelidae). Revista Brasileira de Zoologia, 25: 587-593.
Hirsch, A., L. Dias, W. Martins, S. Porfirio. 2002. Rediscovery of Brachyteles arachnoides hypoxanthus at the Fazenda Corrego de Areia, Minas Gerais, Brazil. Neotropical Primates, 10: 119-122.
Iurck, M., M. Nowak, L. Costa, S. Mendes, S. Ford, K. Strier. 2013. Feeding and resting postures of wild Northern muriquis (Brachyteles hypoxanthus). American Journal of Primatology, 75: 74-87.
Lemos de Sa, R., K. Glander. 1993. Capture techniques and morphometrics for the woolly spider monkey, or muriqui (Brachyteles arachnoides, E. Geoffrey 1806). American Journal of Primatology, 29: 145-153.
Lemos de Sa, R., T. Pope, K. Glander, T. Struhsaker, G. da Fonseca. 1991. A pilot study of genetic and morphological variation in the muriqui (Brachyteles arachnoides). Primate Conservation, 11: 26-30.
Lemos de Sa, R., T. Pope, T. Struhsaker, K. Glander. 1993. Sexual dimorphism in canine length of woolly spider monkeys (Brachyteles arachnoides, E. Geoffrey 1806). International Journal of Primatology, 14: 755-763.
Martins, W., K. Strier. 2004. Age at first reproduction in philopatric female muriquis (Brachyteles arachnoides hypoxanthus). Primates, 45: 63-67.
Martins, W., V. de Oliveira Guimaraes, K. Strier. 2007. A case of infant swapping by wild northern muriquis (Brachyteles hypoxanthus). Primates, 48: 324-326.
Mendes, F., C. Ades. 2004. Vocal sequential exchanges and intragroup spacing in the Northern Muriqui Brachyteles arachnoides hypoxanthus. Annuals of the Brazilian Academy of Sciences, 76: 399-404.
Mendes, S., M. De Oliveira, R. Mittermeier, A. Rylands. 2008. "IUCN 2013: IUCN Red List of Threatened Species Version 2013 Brachyteles hypoxanthus" (On-line). IUCN Red List of Threatened Species. Accessed November 15, 2013 at http://www.iucnredlist.org/details/2994/0.
Mendes, S., F. de Melo, J. Boubli, L. Dias, K. Strier, L. Pinto, V. Fagundes, B. Cosenza, P. De Marco Jr. 2005. Directives for the conservation of the Northern muriqui, Brachyteles hypoxanthus (Primates, Atelidae). Neotropical Primates, 13: 7-18.
Milton, K. 1984. Habitat, diet, and activity patterns of free-ranging woolly spider monkeys (Brachyteles arachnoides E. Geoffrey 1806). International Journal of Primatology, 5: 491-514.
Mittermeier, R., C. Valladares-Padua, A. Rylands, A. Eudey, T. Butynski, J. Ganzhorn, R. Kormos, J. Aguiar, S. Walker. 2006. Primates in peril: the world’s 25 most endangered primates, 2004-2006. Primate Conservation, 20: 1-28.
Mourthe, I., D. Guedes, J. Fidelis, J. Boubli, S. Mendes, K. Strier. 2007. Ground Use by Northern Muriquis (Brachyteles hypoxanthus). American Journal of Primatology, 69: 706-712.
Mourthe, I., K. Strier, J. Boubli. 2008. Seed predation of Mabea fistulifera (Euphorbiaceae) by Northern muriquis (Brachyteles hypoxanthus). Neotropical Primates, 15: 40-45.
Myers, N., R. Mittermeier, C. Mittermeier, G. da Fonseca, J. Kent. 2000. Biodiversity hotspots for conservation priorities. Nature, 403: 853-858.
Possamai, C., R. Young, S. Mendes, K. Strier. 2007. Socio-sexual behavior of female Northern muriquis (Brachyteles hypoxanthus). American Journal of Primatology, 69: 766-776.
Possamai, C., R. Young, R. de Oliveira, S. Mendes, K. Strier. 2005. Age-related variation in copulations of male northern muriquis (Brachyteles hypoxanthus). Folia Primatologica, 76: 33-36.
Printes, R., C. Guimaraes Costa, K. Strier. 1996. Possible predation on two infant muriquis, Brachyteles arachnoides, at the Estacao Biologica de Caratinga, Minas Gerais, Brazil. Neotropical Primates, 4: 85-86.
Strier, K. 1986. The behavior and ecology of the woolly spider monkey, or muriqui (Brachyteles arachnoides E. Geoffrey 1806) Doctoral Thesis. Cambridge: University of Harvard.
Strier, K. 1992. Causes and consequences of nonaggression in the woolly spider monkey, or muriqui (Brachyteles arachnoides). Pp. 110-116 in J Silverberg, J Gray, eds. Aggression and peacefulness in humans and other primates. New York: Oxford University Press.
Strier, K. 1991. Diet in one group of woolly spider monkeys, or muriquis (Brachyteles arachnoides). American Journal of Primatology, 23: 113-126.
Strier, K. 1993. Growing up in a patrifocal society: sex difference in the spatial relations of immature muriquis. Pp. 138-147 in M Pereira, L Fairbanks, eds. Juvenile primates: life history, development, and behavior. New York: Oxford University Press.
Strier, K. 1996. Reproductive ecology of female muriquis (Brachyteles arachnoides). Pp. 511-532 in M Norconk, A Rosenberger, P Garber, eds. Adaptive radiations in Neotropical Primates. New York and London: Plenum Press.
Strier, K., J. Boubli, C. Possamai, S. Mendes. 2006. nthus) at the Estacao Biologica de Caratinga/Reserva Particular do Patrimonio Natural-Feliciano Miguel Abdala, Minas Gerais, BrazilPopulation demography of Northern muriquis (Brachyteles hypoxa. American Journal of Physical Anthropology, 130: 227-237.
Strier, K., P. Chaves, S. Mendes, V. Fagundes, A. Di Fiore. 2011. Low paternity skew and the influence of maternal kin in an egalitarian, patrilocal primate. PNAS, 108: 18915-18919.
Strier, K., L. Dib, J. Figueira. 2002. Social dynamics of male muriquis (Brachyteles arachnoides hypoxanthus). Behaviour, 139: 315-342.
Strier, K., J. Lynch, T. Ziegler. 2003. Hormonal changes during the mating and conception seasons of wild Northern muriquis (Brachyteles arachnoides hypoxanthus). American Journal of Primatology, 61: 85-99.
Strier, K., S. Mendes. 2009. Long-Term Field Studies of South American Primates. Pp. 139-156 in P Garber, A Estrada, J Bicca-Marques, E Heymann, K Strier, eds. South American primates: comparative perspectives in the study of behavior, ecology, and conservation. New York: Springer Science and Business Media.
Strier, K., S. Mendes. 2012. The northern muriqui (Brachyteles hypoxanthus): lessons on behavioral plasticity and population dynamics from a critically endangered species. Pp. 125-140 in P Kappeler, D Watts, eds. Long term field studies of primates. New York: Springer.
Strier, K., S. Mendes, R. Santos. 2001. Timing of births in sympatric brown howler monkeys (Alouatta fusca clamitans) and Northern muriquis (Brachyteles arachnoides hypoxanthus). American Journal of Primatology, 55: 87-100.
Strier, K., T. Ziegler. 1997. Behavioral and endocrine characteristics of the reproductive cycle in wild muriqui monkeys, Brachyteles arachnoides. American Journal of Primatology, 42: 299-310.
Strier, K., T. Ziegler. 2000. Lack of pubertal influences on female dispersal in muriqui monkeys, Brahchyteles arachnoides. Animal Behaviour, 59: 849-860.
Strier, K., T. Ziegler. 2005. Variation in the resumption of cycling and conception by fecal androgen and estradiol levels in female Northern muriquis (Brachyteles hypoxanthus). American Journal of Primatology, 67: 69-81.
Tabacow, F., S. Mendes, K. Strier. 2009. Spread of a terrestrial tradition in an arboreal primate. American Anthropologist, 111: 238-249.
Tokuda, M., J. Boubli, P. Izar, K. Strier. 2012. Social cliques in male northern muriquis Brachyteles hypoxanthus. Current Zoology, 58: 342-352.
Tolentino, K., J. Roper, F. Passos, K. Strier. 2008. Mother–offspring associations in Northern muriquis, Brachyteles hypoxanthus. American Journal of Primatology, 70: 301-305.
Vieira, L., S. Mendes. 2005. Presence of the muriqui (Brachyteles hypoxanthus) in a rural property in the vicinity of the Augusto Ruschi Biological Reserve, Santa Teresa, Espirito Santo. Neotropical Primates, 13: 37-39.
Wiederholt, R., E. Post. 2011. Birth seasonality and offspring production in threatened neotropical primates related to climate. Global Change Biology, 17: 3035-3045.
Zingeser, M. 1973. Dentition of Brachyteles arachnoides with reference to Alouattine and Atelinine affinities. Folia Primatologica, 20: 351-390.
da Silva Junior, W., J. Meira-Neto, F. da Silva Carmo, F. de Melo, L. Moreira, E. Barbosa, L. Dias, C. da Silva Peres. 2009. Habitat quality of the woolly spider monkey (Brachyteles hypoxanthus). Folia primatologica, 80: 295-308.
da Silva Junior, W., F. de Melo, L. Moreira, E. Barbosa, J. Meira-Neto. 2010. Structure of Brazilian Atlantic forests with occurrence of the woolly spider monkey (Brachyteles hypoxanthus). Ecological Research, 25: 25-32.
de Cassia Bianchi, R., S. Mendes. 2007. Ocelot (Leopardus pardalis) Predation on primates in Caratinga Biological Station, southeast Brazil. American Journal of Primatology, 69: 1173-1178.
de Cassia Bianchi, R., S. Mendes, P. De Marco Junior. 2010. Food habits of the ocelot, Leopardus pardalis, in two areas in southeast Brazil. Studies on Neotropical Fauna and Environment, 45: 111-119.
de Melo, F., B. Cosenza, D. Ferraz, S. Souza, . Nery, M. Rocha. 2005. The near extinction of a population of Northern muriquis (Brachyteles hypoxanthus) in Minas Gerais, Brazil. Neotropical Primates, 13: 10-14.