Patas monkey
Erythrocebus patas

SOCIAL ORGANIZATION AND BEHAVIOR

Two distinct types of group organization can be observed among patas monkeys over the majority of the year. The first type is the polygynous group of variable numbers of females and one male. The other type is that of all-male groups although occasionally mixed-sex groups with two adult males have been known to occur (Hall 1965; Struthsaker & Gartlan 1970; Gartlan 1974). During mating season, which corresponds with the summer rainy season, other males may enter the single male group to copulate. There is little to no intra-group mobility among females and they stay with their natal group for life. Most likely, females determine movements of the group and sleeping sites because they are more familiar with the home range of the group than the transitory males (Chism et al. 1984).

It was long debated if a defined dominance hierarchy of female patas monkeys existed but at present, the consensus is that it does exist. This hierarchy is not as well defined or as firm as those of other Cercopithecines and it is likely that the patas monkey dominance hierarchy is not kin-based (Chism & Rogers 2002). Nakagawa (1992) supports the view of a discrete hierarchy of female patas monkeys and suggests that the male is always at the periphery of the group. The hierarchy of patas females remains somewhat static once established and is maintained through submissive and aggressive actions between the patas females. Kinship relationships between females also serve to help keep a patas group together (Nakagawa 1992). In one captive study, when a new group was created, the adult females formed a dominance hierarchy within several months through agonistic interactions (Loy & Harnois 1988). There is evidence of post-conflict reconciliation among patas females with increases in contact between former adversaries following agonistic interactions (York & Rowell 1988). The male interacts infrequently with the females of his group and spends most of his time at its periphery. It is from this position that the male spends a large part of his time scanning the landscape for predators or males from other groups who may challenge him (Hall 1965; Nakagawa 1992). In captivity, this model of the sole male at the edge of the group holds, with the male aloof and indifferent to intra-group social interactions (Hall & Mayer 1967).

Grooming plays an important role in patas social organization and can indicate hierarchies within a group as well as relationships between individuals doing the grooming (Rowell & Olson 1983). High status within a patas hierarchy group is reflected by grooming frequency. Nakagawa (1992) observed that high status female patas received more grooming than lower status group members. Grooming also serves to facilitate allomothering, as grooming of a mother may allow the groomer access to the motherÕs infant (Muroyama 1994). Status or rank also seems to play a role in grooming of the adult male within a polygynous patas group. In captivity, most of the grooming of the resident male was done by high status females (Loy & Harnois 1988). There is evidence that the smaller the patas group, the higher the instance of allogrooming (Chism & Rogers 2002). This higher rate of grooming with smaller size groups most likely serves to reinforce group cohesion as a smaller group is more vulnerable to outside interference.

The males choose to leave their natal group by puberty or are driven out when they reach sexual maturity by the resident adult male (Gartlan 1974). Sometimes the male will leave his natal group with a brother, a kin relation which may help them both survive (Chism 1999). This displacement occurs typically at around three years of age and they may remain solitary or in all male groups until they are fully grown at around five years of age (Chism et al. 1988). The purpose of the all-male patas group appears to be to provide safety for young or infirm males and for protection against predators and other threats (Ohsawa 2003).

It was long believed that patas groups organized themselves in polygynous mating systems but now it is assumed that this type of mating system is the exception rather than the rule (Harding & Olson 1986). One male is present through the year with a group of females but other males infiltrate the group during the mating season to breed with group females (Harding & Olson 1986; Carlson & Isbell 2001). In fact, the flow of males into and out of groups is best described as dynamic, particularly in the mating season (Chism & Rowell 1986). In at least one study it was shown that these sneak matings are initiated by the females in the group (Ohsawa 1993). Some years, patas groups may remain exclusive single-male mating systems while in subsequent years the same group may be a multi-male system (Carlson & Isbell 2001).

Most supplantation of the single male in the polygynous groups occurs during the mating season and serves to provide the challenger with access to mating with resident females. Supplantation occurs when a male from another group challenges the single male and may be accomplished through fighting and chasing (Ohsawa 2003). Depending on the victor, either the resident male is removed from his position as the sole male or the challenger remains peripheral. When challenged by an extra-group male, the resident male has a higher probability of winning the fight (Chism & Rogers 1997). Supplantation by a challenger male is sometimes followed by a short-lived multi-male polygynous mating system in which several males are actively breeding within a group (Ohsawa et al. 1993). This is most likely the result of the new resident male being too preoccupied with mating to chase other males away (Ohsawa 2003).

Patas polygynous group size is quite variable, from 20 to as large as 76 individuals (Enstam et al 2002; Ohsawa 2003). It appears that all-male groups are typically smaller than the polygynous groups with Cameroonian all-male group observed with 15 to as few as two individuals (Struhsaker & Gartlan 1970; Ohsawa 2003). Inter-group encounters are typically agonistic but rarely physical and serve to assist in group resource defense (Chism et al. 1984).

Frequently, a patas monkey will continuously scan its environment and monitor its surroundings both quadrupedally and bipedally and, if available, will seek out a high vantage point to do so (Rowell & Olson 1983; Chism 1999; Enstam & Isbell 2004). This important behavior serves several purposes. The scanning alerts the patas in a group to predators and to non-group patas (Hall 1965; Nakagawa 1992). In addition, the scanning may serve as a social monitoring process and help with group coherence (Rowell & Olson 1983). Patas scan not only the landscape but also each other so that they are constantly aware of other patas' actions which may serve to reduce agnostic encounters. This may also assist with the maintenance of acceptable distances between patas individuals which avoids agonism (Rowell & Olson 1983; McNelis & Boatright-Horowitz 1998). Because the patas monkey is a relatively silent species compared to other monkeys, the constant visual monitoring of the landscape as well as each other can serve as a type of communication in that most individuals will notice quickly if something is amiss with another individual (Rowell & Olson 1983).

REPRODUCTION

Patas monkeys have a clearly defined conception and birth season. Typically conception occurs in the summer wet season and births occur in the winter dry season (Struhsaker & Gartlan 1970; Nakagawa et al. 2003; Chism et al. 1983). Patas are able to obtain more nutrition in the dry season than in the wet and this may be one explanation for the seasonality of their reproduction (Nakagawa 2000). Another potential reason for such profound birth seasonality may be the availability of food during the breeding season which allows the prior year's infant to be weaned, enabling the mothers to become pregnant again (Chism et al. 1984). In captivity, the patas monkey does not display this reproductive seasonality (Sly et al. 1983). In addition, wild patas monkeys typically give birth during the day which may be an adaptation to reduce the risks associated with nocturnal predators. Patas monkeys are vulnerable to nocturnal predators and rely on concealment at night to avoid said predators (Chism et al. 1983).

The patas monkey in some cases participates in consortships in which a male and female will attend to, stay in close proximity to, and monitor one another. A consortship, as described above, lasts more than thirty minutes. During the course of this association, the male and female patas monkey will copulate. In addition, if other patas individuals approach, the two patas in consort will move even closer together (Harding & Olson 1986). These pairings may allow unfamiliar patas to assess one another's reproductive fitness and allow the pair of monkeys to size each other up (Harding & Olson 1986).

In captivity, the average gestation period for a female patas monkey is 167 days (Sly et al. 1983). As a patas juvenile is fully able to take care of itself from six to seven months of age, this allows females to be ready to bear young again by the next breeding season and to essentially reproduce at the maximum rate possible (Chism et al. 1984). The age at first conception in females in both the wild and in captivity is approximately 2.5 years resulting in the first birth at around three years of age (Chism et al. 1984; Nakagawa et al. 2003). The male matures slightly later and can sire offspring at four years old, but rarely is able to do so due to his inability to access females (Rowell & Chism 1986). The average ovarian cycle of the captive patas female is 30 to 33 days and a degree of synchronization of estrus has been observed in a specific patas group (Rowell 1976; Loy et al. 1978; Rowell & Hartwell 1978).

A marked color change in the facial hair of female patas is observed during pregnancy. This has been observed in two separate studies in captivity. The facial hair begins to lighten in the second trimester of pregnancy and is at its maximum lightness between 1.5 and 2.5 months postpartum (Loy 1974; Palmer et al. 1981). Approximately three months postpartum, a darkening process begins returning the face to close to its pre-pregnancy color (Loy 1974). This color change may be the result of hormonal changes associated with pregnancy and may have a use in delineating the reproductive histories of females as the face does not always completely revert to pre-pregnancy coloration (Palmer et al. 1981). The bright blue color of the patas scrotum appears to play some role in competition for access to females, but its color exhibits no correlation with season, age, or health (Bercovitch 1996).

As to which sex initiates copulation, it appears that this is related to what type of mating system is in operation at any given time. In years when a multi-male/multi-female mating system is in place, males are much more likely to initiate copulation than in polygynous years. Females showed the converse, initiating copulation at a much higher rate during single-male mating years than in multi-male system years (Carlson & Isbell 2001). The female solicitation posture consists of the female placing herself in front of a male facing away from him in a crouching position and looking back at him while blowing air into her cheeks. She also may drool and curl her tail (Chism et al. 1984).

There has also been at least one instance of probable infanticide by a patas male observed in the wild (Enstam et al. 2002). The reason for this killing is probably to increase mating opportunities for the male because he may then subsequently mate with the mother. Hrdy (1974) suggests that infanticide is beneficial when a male may only have a short time to mate before being supplanted by another male and when access to females is limited.

PARENTAL CARE

All patas females participate in allomothering. At present, it is not obvious what the benefits of allomothering are, although they may be related to social hierarchy based on who receives allomothering and who does the allomothering (Muroyama 1994; Nakagawa 1995). This behavior may also be related to an altruistic relationship between adult females (Nakagawa 1998). On at least one occasion in Cameroon, patas females of one group were observed to kidnap an infant from a different group, allomother it for a while and eventually abandon it (Nakagawa 1995). Allomothering may also serve to strengthen social interactions and group cohesion. In captivity, infant patas females were observed to receive significantly more allomothering from non-kin females that the male patas infants (Loy & Loy 1987). This preference to allomother female infants serves to integrate and reinforce relationships within the female natal group and to drive the males to their position at the periphery of the group. In captive studies, patas adult males seldom interact with mothers with infants and their behavior could even be described as avoidant (Chism 1986).

Patas monkeys demonstrate one of the shortest interbirth intervals of any Cercopithecine, averaging about one year between births (Chism et al. 1984; Nakagawa et al. 2003). The patas infant must be fully independent by one year of age as it will be displaced by a new infant. Orphaned patas infants have been observed to survive in the wild without being adopted as early as seven months of age (Chism et al. 1984).

In captivity, from birth until the fourth month of life, male and female infants receive comparable amounts of grooming and attention from their mothers. After this period of time, there is a marked increase in grooming and attention paid to female infants while grooming of the male infants remains the same (Loy & Loy 1987). This again shows the strong matrilineal bonds between adult females. After the fifth month of life, contact between the mother and her infant of either sex decreases steadily (Chism 1986). During this time the infant will continue to nurse at night, but represents only a small energetic cost to the mother. This nursing is merely a supplemental food source as the infant is quickly learning how to forage on its own. Complete weaning of the infant only occurs when the mother gives birth to a new infant, typically around one year of age (Chism 1986).

Patas infants are born completely black in color and remain so for the first three months of their lives. In the subsequent three months, the natal coat will begin to fade to the reddish coat of the adult (Palmer et al. 1981). In a specific captive study, patas infants were observed to typically start eating solid food around the seventh week, exhibit play behavior in the eighth week, and bipedally scan at the third month. For the first several months, the predominant posture of an inactive mother with a young infant is that of cradling which starts to steadily decrease in the third month. This may assist the infant in its suckling posture and to keep it warm (Chism 1986). In a long term study, the mortality rate of infants and one year-old juveniles averaged 20% (Nakagawa et al. 2003).

COMMUNICATION

Patas vocalize infrequently and tend to move quietly (Chism & Rowell 1988). They are a relatively silent species with few physical cues that rely on visual communication to avoid agonistic interactions within groups (McNeilis & Boatright-Horowitz 1998). Visual contact serves to transfer information about important occurrences within the patas environment quickly through constant monitoring of not only the environment, but other patas within a group as well (Rowell & Olson 1983). Patas rely on an "adaptive silence" and prefer not to give away their locations to predators (Hall 1967). Patas exhibit a low frequency of contact calling between individuals which may be as a result of the open nature of their habitat which facilitates visual contact instead (Nakagawa 1992).

Patas alarm calls are the best documented of their vocalizations. These calls are directed to warn other patas of a threat and are uttered mainly in response to mammalian predators. There are various alarm calls which in many cases are predator specific however males only utter the "bark grunt" in response to all predators. This type of grunt is also vocalized by males in response to the approach of extra-group male patas (Enstam & Isbell 2002). Patas monkeys other than adult males exhibit several discrete alarm calls which they use to warn the group of danger. In response to jackals and wildcats, a "cough" alarm call is uttered. "Loud chutter" is the alarm call associated with baboons, domestic dogs, jackals and wildcats. A "nyow" alarm call is the response to baboons, domestic dogs and lions. Finally, a "quiet chudder" or a "gecker" are calls both associated with snakes and the "gecker" may also be used to warn of raptors (Enstam & Isbell 2002). Other types of vocalization used by patas monkeys are those used in allomothering interactions. These consist of the allomother's "moo" and the infants' "want" call. The infant's "want" call serves to attract related, unrelated, and even unfamiliar allomothers. The allomother's "moo" is typically uttered when approaching the infant to be allomothered (Nakagawa 1998).

Another type of possible communication is that of olfactory communication. In captivity, patas were observed to occasionally approach another individual and perform a discrete "nose to mouth" gesture with the ostensible purpose of ascertaining what the other individual had been eating (Rowell & Olson 1983).

One documented captive patas communicative display is that of the Grimace-Gecker in which the patas displays its teeth to another. Originally suggested to be a submissive/appeasement signal, this display has been argued not to convey such a message. Regardless, the display appears to be discrete and to serve some unknown communicative purpose (Jacobus & Loy 1981; Loy et al. 1993)

Content last modified: December 18, 2006

Written by Kurt Gron. Reviewed by Karin Enstam.

Cite this page as:
Gron KJ. 2006 December 18. Primate Factsheets: Patas monkey (Erythrocebus patas) Behavior . <http://pin.primate.wisc.edu/factsheets/entry/patas_monkey/behav>. Accessed 2009 November 7.