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Uakari group size is extremely variable, from as small as a pair to a hundred individuals and perhaps as many as 200 individuals with many observations intermediate between the largest and smallest estimates and observations. Most groups appear to be < 70 individuals and significantly smaller groups are likely subdivisions of larger ones (Mittermeier & Coimbra-Filho 1977; Ayres & Johns 1987; Bartecki & Heyman 1987; Aquino 1988; Ayres 1990; Defler 1991; Heymann 1992; Boubli 1994; Barnett & Brandon-Jones 1997; Boubli 1997a; Aquino 1998; Defler 1999; Bennett et al. 2001; Bowler 2002; Ward & Chism 2003; Barnett et al. 2005a). Groups numbering over 100 individuals are the largest groups of any New World primate (Boubli 1994). Numbers are variable between populations as well, with some authors placing the maximum group size far lower, around 30 individuals (Barnett et al. 2000). This large variation in observed group size might be indicative of a fission-fusion type of social organization (Defler 1999). However, some long-term observations did not observe fluctuating group size or fission-fusion, while others recorded a seasonal dispersal of the larger groups into mating pairs and bachelor groups (Ayres 1990; Boubli 1997a; 1997b).

C. calvus rubicundus
Cacajao calvus rubicundus
Photo: Roy Fontaine

Larger groups aggregate particularly at times of more abundant food but also potentially the result of other factors (Defler 1999; Aquino 1998). Some researchers have observed large groups breaking into smaller subunits during travel and during foraging, subunits that sometimes last for several days and some researchers postulate that perhaps there could be several levels of social organization within uakari groups (Ayres & Johns 1987; Bartecki & Heyman 1987; Ayres 1989; Heymann 1992; see also Grüter & Zinner 2004 for speculation). Groups are multi-male/multi-female and are usually composed of multiple adult males and females, subadults (including juveniles and infants) and group membership is roughly evenly divided between the sexes (Ayres 1989; Boubli 1997a; 1997b; Aquino 1998). However, bachelor male groups of up to 8 males have been seen in certain times of the year (Ayres 1990).

The group is dispersed as it travels, and comes together at large food patches and during rest periods and members of subgroups can be spread as far as 1-2 km (0.6-1.2 mi) from one another (Ayres 1989; 1990; Boubli 1999). Contact within the group is maintained through calling (Boubli 1997b; 1999).

In general, very little is known about the social structure of wild uakari troops. In the wild, if the group is disturbed one male has been seen to remain behind and vocalize in the direction of the intruder although what this means about the social structure of the troop remains to be clarified (Barnett et al. 2005a). It is suggested that wild uakari social organization is non-hierarchical (Barnett & Brandon-Jones 1997). However, a dominance hierarchy is seen in captive uakaris, maintained predominantly through fighting (Fontaine & DuMond 1977; Fontaine 1981). Further, in the wild, males have been seen aggressively interacting although again, the meaning of these interactions is ambiguous, and aggression appears to be very rare (Barnett et al. 2005a; Barnett 2008). During rest, grooming sometimes occurs and is initiated by female uakaris (Aquino 1998). In captivity, grooming is frequent and helps maintain friendly social relationships. However, most of the time individual uakaris are usually at least several meters from the nearest conspecific (Fontaine & DuMond 1977). Grooming is rarely seen in the wild, at least for C. m. ouakary (Barnett 2008).

Aggression in captivity is signaled by branch shaking, rocking, breaking, carrying and dropping. It is also signaled by hind leg extension and rubbing, the bouncing of the hindquarters, strutting, and the urine-washing of the chest (Fontaine & DuMond 1977). Further, dominant individuals in captivity intervene in disputes between other group members (Fontaine & DuMond 1977).

Tail-wagging is almost constant in uakaris (Boubli 1997a). Though Fernandes (1993) considers this to be a sign of alarm, Defler (2004) considers it a sign of contentment in C. m. ouakary, noting that an alarmed or fearful animal will curl its tail under its body, like a submissive dog.

In captivity, play is seen not only involving sub-adults, but also between adult individuals (Fontaine 1981). Play is extensive in young wild C. m. ouakary (Barnett 2008).


Both species of uakaris appear to have birth seasons or peaks. C. calvus sees a peak in births during the dry season, between October and November while C. melanocephalus has a birth season between March and April (Ayres 1986 cited in Norconk 2007; Ayres 1990; Boubli 1997a; Defler 2004; Barnett 2005). However, births can occur outside of the birth season and new evidence that C. m. ouakary might have two annual breeding peaks (Defler 2004; Barnett 2008). Wild births are single and in the wild and in captivity, the interbirth interval is estimated roughly at two years (Fontaine & DuMond 1977; Defler 2004; Barnett 2005).

C. calvus rubicundus
Cacajao calvus rubicundus
Photo: Roy Fontaine

In captivity, females show their receptivity by directing their hindquarters at a male and raising their tail (Fontaine & DuMond 1977). Females are receptive only about 3 or 4 days per ovarian cycle (Fontaine & DuMond 1977). In captive individuals, copulation is usually dorso-ventral with the male behind the female although in at least one wild observation, face-to-face copulation was seen (Fontaine & DuMond 1977; Boubli 1997a). In the wild, copulation generally lasts less than two minutes (Ayres 1990). In captivity, post-copulation, genital sniffing and grooming follows (Fontaine & DuMond 1977). Gestation is approximately six months (Ayres 1990). Data about the age of reproductive maturity in uakaris is extremely limited but based on exceedingly small samples, males in captivity are reproductively successful at 6 years old while a single female was reproductively mature at 3 years old (Fontaine & DuMond 1977).


Almost all of the available information on parental care and infant development comes from a single semi-natural captive population of C. calvus in Florida observed over twenty years ago (see Fontaine & DuMond 1977; Fontaine 1981). Neither C. melanocephalus sub-species has ever been bred in captivity (Barnett 2005). Size at birth is at best 10% of that of the mother and the face and head are grayish and have hair (Fontaine 1981; Ayres 1990). All births occurred at night in an outdoor captive enclosure and for the first three months of life, the mother will reduce her interactions with the rest of the group (Fontaine & DuMond 1977; Fontaine 1981). The infant is not very active during its first month (Fontaine & DuMond 1977). Solid foods are first consumed around three months old. From birth until the third or fourth month, the infant is carried ventrally and to the side. After this age the infant rides on the mother's back (Fontaine 1981). From three months old to one year old the face will start to transition from grey to pink, however at this time the head has thick hair, in contrast to the adults, a condition which persists through the second year of life. The baldness characteristic of C. calvus species develops in the third year (Fontaine & DuMond 1977; Fontaine 1981). In the sixth and seventh months of life, play starts with other infants. In the wild, while playing, juveniles vocalize a characteristic "hissing" sound (Boubli 1997a). Towards the end of the first year in captivity, the infant starts moving around independently (Fontaine 1981). Full weaning occurs in the 2nd year of life, is complete by two years old, and involves little weaning conflict (Fontaine 1981).

In the wild, C. calvus infants nurse for 3-5 months, and start eating solid foods between 4 and 6 months of age. By one year old, the diet approximates the foods eaten by adult uakaris (Ayres 1990). Further, in C. melanocephalus, adult males are patient and tolerant of juveniles in the wild (Boubli 1997a).


The wild contact calls of uakaris consist of "keeks," "hics" and "chics" which are described as sounding roughly bird-like and are heard virtually non-stop (Boubli 1997a; 1997b; Ward & Chism 2003; Barnett 2005). Uakari vocalizations are best studied in captivity in C. calvus, and can be roughly separated into two categories, high- ("hic," "chyook," "chick," "wee-ook," "rhork," "kreek," "wa," "kik" and "rhä") and low-amplitude vocalizations ("purr," "hiss," and "keh") (Fontaine 1981). In captivity, males use visual signals more than vocalizations, while females and immature individuals use vocalizations more than visual signals. Vocalizations are often contagious between individuals and are sometimes combined into sequences. "Hic," "chyook," and "chick" respectively are uttered in situations of increasing stimulus (Fontaine 1981). "Wa" vocalizations are loud and usually emitted during inter-individual fights and convey intense fear (Fontaine 1981; Ward & Chism 2003). "Kreek" and "rhork" convey less intense fear. "Purr," "hiss" and "keh" vocalizations are uttered in friendly contexts. "Rhä" is heard during aggression and "kik" is motivated by fear during play (Fontaine 1981). Calls heard in the wild include the "purr" which is heard in affectionate situations, "ki-ki-kis" and "harsh screams" which are contact calls, "wai-wah-wah," which is uttered during arousal, "chee-chee" which is a danger call, "screams" which are given by animals which are being punished, and the "harsh ehh" which is a play vocalization (Defler 2003 cited in Defler 2004).

In the wild, tail-wagging commonly occurs at the same time as vocalization (Walker & Ayres 1996). A wagging tail likely communicates the well-being of the animal while a lowered tail communicates a tense situation to other uakaris (Defler 2004). In captivity, tail-wagging is seen in situations of general arousal (Fontaine 1981).

In captivity, aggressive adult male visual signals include the single leg jerk, hindquarters bounce, branch slapping and arm raising, quadrupedal stand and stare, strut, branch rocking, and urine washing. Other agonistic visual signals include leg extension, arched back, piloerection, branch shaking, breaking, and dropping (Fontaine 1981). Further, the uakari draws on a canon of facial expressions which communicate a spectrum of meanings from agonism to affiliation to appeasement to fear as well as other meanings (see Fontaine 1981 for full description of facial expressions). Tactile patterns which the uakari uses to communicate through touch include allogrooming, body contact, contact aggression, and dorsal mounting, embracing, and sidling (Fontaine 1981).

In the wild, visual signals include penile displays, piloerection, tail wag in upright position, tail-down, posterior display, and urine washing (Defler 2003 cited in Defler 2004).

Olfactory communication in captivity consists of genital sniffing and licking, anal rubbing, rubbing substances in the fur, and urine washing (Fontaine 1981). The sternal glands present in both sexes might be involved in olfactory communication (Fontaine & DuMond 1977).

Content last modified: July 21, 2008

Written by Kurt Gron. Reviewed by Adrian Barnett.

Cite this page as:
Gron KJ. 2008 July 21. Primate Factsheets: Uakari (Cacajao) Behavior . <>. Accessed 2014 April 16.