Vervet Monkey (Chlorocebus pygerythrus) Fact Sheet: Behavior & Ecology

Daily activity

• Diurnal, active in daylight
  • Gather near sunrise, usually before 08:00 hr (Struhsaker 1967a,b)
  • Disperse for daily foraging
    • Group members often are spread across substantial distance, 274 m (c. 900 ft) in one study (Struhsaker 1967b)
  • Travel peaks in morning and afternoon
    • 07:00-10:00 and 16:00-19:00 hr (Struhsaker 1967a)
  • Visit watering location typically near early afternoon
    • 13:00-15:00 hr (Struhsaker 1967a)
• At night, sleep in trees (Struhsaker 1967a,b)
  • Sleep at the outer ends of the highest branches (Isbell and Enstam-Jaffe 2013)
    • Prefer tall and large trees (Isbell and Enstam-Jaffe 2013)
  • Group may spread out over a large distance; rarely does the entire group sleep within a single canopy (Struhsaker 1967b)
    • Linear distance of c. 700 m (c. 2,300 ft) recorded in one study (Struhsaker 1967a,b)
• Distribution of daytime activity (from Isbell and Young 1993 unless otherwise noted)
  • Feed and scan their surroundings most of the day, 60-80% of the time
    • Roughly equal time spent in both activities
    • Males may scan more than females
  • Move (walk, run, climb, etc.) less often, 12-18% of activity
  • Self-groom or allogroom occasionally, < 10% of activity
    • Females allogroom more than males
  • Rest on the ground or in trees, < 10% of activity
    • Lie (on the side) or sit upon the ground (Struhsaker 1967e)
      • Sit on ischial callosities, thighs often pressed against the chest
      • Hands hang down at sides or rest on the feet (Struhsaker 1967e)
    • Lie or sit in trees (Struhsaker 1967e)
      • Sit with feet propped against the tree; tail wrapped around a branch (Struhsaker 1967e)
      • Lie with legs straddling a branch (Struhsaker 1967e)

Size variable

• Factors influencing range size (Isbell and Enstam-Jaffe 2013; Struhsaker 1967a,b)
• Group size
• Presence of neighboring groups
• Vegetation distribution and composition
• Characteristics of groups with the largest ranges
• Typically held by large groups, with numerous females (Cheney and Seyfarth 1987)

Estimates of range size

• 5-103 ha (0.02-0.4 mi²) (Isbell and Enstam-Jaffe 2013)

Territorial overlap can be considerable

• 4-57% overlap
• Based pm reports of one population observed across several decades (Pasternak et al. 2013)

Social; live in groups

• Group composition
  • 2 or more females, their offspring and multiple males (Isbell and Enstam-Jaffe 2013; Isbell et al. 2002)
    • Rarely form single male, multi-female groups (Isbell and Enstam-Jaffe 2013)
    • Sex ratio c. 1:1 (Struhsaker 1967a, b)
    • Unlike "harem" system typical of patas monkeys and hamadryas baboons (Enstam and Isbell 2002)
  • Group size variable across distribution (Struhsaker 1967b)
    • Range: 7-53 (Isbell et al. 1998b; Struhsaker 1967a,b)
    • < 40 typically (Pasternak et al. 2013; Isbell and Enstam-Jaffe 2013)
• Group dynamics
  • Females remain in their natal (birth) groups, most often (Isbell and Enstam-Jaffe 2013)
  • Males disperse from natal groups (Cheney and Seyfarth 1983; Isbell and Enstam-Jaffe 2013)
    • Most immediately join another nearby group
    • Seldom solitary (Cheney and Seyfarth 1983)
• Defend territory against neighboring groups (Struhsaker 1967a)

Intragroup dominance

• Linear dominance hierarchy within each sex (Isbell and Pruetz 1998; Struhsaker 1967b)
  • Subordinates are displaced to give higher-ranked individuals access to food, grooming, and spatial position (Struhsaker 1967b)
• Female dominance
  • Individual position is largely stable (Isbell and Enstam-Jaffe 2013; Isbell and Pruetz 1998)
  • Mother and daughter hold similar positions (Isbell and Enstam-Jaffe 2013)

Active defense against incursion by outsiders (from Struhsaker 1967e)

• Do not patrol territories
  
• All group members (except infants) participate in defense
• Tail often held erect during encounters

Vocalize to announce proximity of a foreign group (Struhsaker 1967c)

• Unique adults and juveniles calls
• Aarr call, given by adults
• Wawoo call, given only by infants

Defensive behaviors

• Herd trespassers
  • Residents walk in close formation, advancing on and supplanting the trespassers (Struhsaker 1967e)
• Shake tree branches
  • Residents run and leap through trees, ricocheting off branches; pausing to grab and violently shake limbs with the arms and legs (Struhsaker 1967e)

Aggression

• Primarily peaceful
  • Agonistic interactions observed at least once each day (Lancaster 1971)
    • One female threatens another about once every 6 hours, one study (Cheney and Seyfarth 1987)
    • Males commonly threaten one another with non-physical actions; higher ranking individuals more frequently than their lower ranked counterparts (Freeman 2012)
      • Aggression increases during the breeding season (Freeman 2012)
  • Physical contact rare (Struhsaker 1967c)
    • Most frequently threaten or chase one another (Struhsaker 1967c)
    • Wounds may be severe (Freeman 2012)
      • Most frequently on the tail, limbs, head, and face (Freeman 2012; Struhsaker 1967e)
      • Less commonly on the back or shoulders (Struhsaker 1967e)
      • Males are more likely to have wounds than females; particularly during the breeding season (Freeman 2012)
• Aggressive behaviors
  • Moderate intensity displays (Cheney and Seyfarth 1989; Freeman 2012; Struhsaker 1967d)
    • Stare and eye flash; as with other cercopithecines (Struhsaker 1967d,e)
      • Pointed, prolonged stare; held for 3-5 seconds (Struhsaker 1967e)
      • Used in defense and aggression (Struhsaker 1967e)
    • Eyelid display infrequent, though common in other cercopithecines (Struhsaker 1967d,e)
      • Retract the brow to expose the pinkish eye lids
      • Often combined with exposure of the canine teeth (Freeman 2012)
    • Head bob
      • Bob head back and forth along the sagittal plane; directed toward another individual (Struhsaker 1967d)
        • Severity of threat increases when accompanied by a jerk of the forequarters (Struhsaker 1967d)
      • Performed while sitting or standing quadrapedally (Struhsaker 1967e)
    • Forequarters jerk (Struhsaker 1967e)
      • Chest and shoulders jerked back-and-forth and up-and-down; directed toward the display recipient
    • Lip smack (Freeman 2012; Struhsaker 1967c)
      • Rapid, repetitive opening and closing of the lips
      • Gives the effect of a popping noise
  • Severe intensity displays
    • Chase, lunge, grab, hit, and bite (Cheney and Seyfarth 1989; Struhsaker 1967c)
• Form coalitions within groups
  • One monkey solicits the aid of 1-2 others (1 most commonly) in an agonistic encounter against another vervet (Struhsaker 1967b)
    • High ranking individuals rarely, if ever, solicit assistance
    • Low ranking individuals uncommonly solicited for assistance; most frequently observed requesting help from others
  • Membership is not fixed, though most are associations of relatives (Cheney and Seyfarth 1987; Struhsaker 1967b)

Affiliative Behaviors

• Allogrooming
  • Hands spread hairs, and mouth or hands remove particles (Struhsaker 1967e)
    • Groomer may smack its lips and chatter its teeth
  • Mothers are groomed for longer periods of time than non-mothers; most frequently by juvenile females (Fruteau et al. 2011; Lancaster 1971)
    • Mothers accept grooming from non-mothers in exchange for handling their infants (Fruteau et al. 2011)
    • Grooming time decreases both when the number of available infants per female increases and when infants grow older (Fruteau et al. 2011)
• Allomothering, care of young by individuals other than the mother(Fairbanks 1990)
  • Non-mothers touch, cuddle, carry and groom infants; males never observed caring for infants (Lancaster 1971)
    • Juvenile females commonly seen with infants during the reproductive season (Lancaster 1971)
    • Infants > 4 months of age rarely continue to receive motherly attentions (Lancaster 1971)
  • Exchange benefits (from Fairbanks 1990 unless otherwise noted)
    • Mothers receive increased grooming from non-mothers and more assistance in the care of their infants
      • May decrease the interval between consecutive births
    • Non-mothers gain experience in the caretaking and carrying of infants
      • May increase the odds for successfully raising their first-born infant
      • Inexperienced juveniles often hold infants against the chest and walk on three legs; some even run bipedally and press the infant to the chest with both arms (Lancaster 1971)
  • Substantial amounts of an infant's life may be spent away from its mother, according to a study of captive vervets (Fairbanks 1990)
• Huddle together in heavy rainstorms(Struhsaker 1967b)
  • Presumably for warmth and shelter

Play

• Solitary play uncommon(Struhsaker 1967e)
  • 1 instance of an infant playing with a feather observed in a 12 month study
• Juveniles form play groups(Lancaster 1971)
  • Active after morning feeding when adults typically rest or groom (Lancaster 1971)
    • Often at considerable distance from adult group members (Fagan 2002)
  • Infants enter the juvenile play group by 3 months of age (Lancaster 1971)
• Forms of play
  • Common forms of play
    • Gambol, chase, grapple, wrestle, mouth (Lancaster 1971; Pellis et al. 2014; Struhsaker 1967e)
  • Uncommon forms of play
    • "Tug-of-war"; two individuals grab (with mouth or hands) opposite ends of grass or a piece of bark and pull in opposite directions (Struhsaker 1967e)
    • "Hide-and-seek"; monkeys leap and bound through tall, green grass in chase of one another, one often crouches low to conceal itself (Struhsaker 1967e)
  • Mouths typically held open when at play (Pellis et al. 2014; Struhsaker 1967e)
    • Participates often deliver restraited bites; most often on the opponents head or neck (Pellis et al. 2014)
  • Playmates commonly mount one another (Struhsaker 1967e)
• Time spent in play
  • Males may play more than females; as demonstrated in the closely related green monkey (Fairbanks 2002)

Other

• Individuals entwine tails(Struhsaker 1967e)
  • When closely seated on a tree branch; possibly for balance
• "Kiss" (muzzle-muzzle)(Struhsaker 1967e)
  • Muzzles of two monkeys come into contact, often occurs during grooming
  • Initiator may place one of both hands behind the recipients neck or head during contact
  • Meaning unclear
    • Possibly to test or transfer food or a gesture of nonaggression or appeasement (Lycett and Henzi 1992)

Vocalization

• Highly vocal with numerous distinct calls
  • > 30 physically and/or audibly distinct sounds (Isbell and Enstam-Jaffe 2013; Struhsaker 1967c)
  • 'Squeals', 'screams', 'grunts', 'chutters', 'wrrs', 'waas', and 'aarrs' (Isbell and Enstam-Jaffe 2013)
• Alarm Calls (see complete list in Struhsaker 1967c)
  • 6-7 distinctive calls; to identify the nature and proximity of a predatory threat
    • High-intensity, elevated threat calls; directed toward a major predator in close proximity
      • Rraup, threat-alarm-bark, and chirp
    • Moderate-intensity, moderate threat call; indicates sudden movement of a minor mammalian or avian predator
      • Nyow!
    • Low-intensity, minimal threat call; warns of close proximity of a minor mammalian predator
      • Uh!
    • Chutters
      • Variable forms appear to identify specific predators, E.g. snakes, humans
  • Most (observed) calls are the response to perceived mammalian or avian predators (Baldellou and Henzi 1992; Enstam and Isbell 2002)
  • Response to calls (Enstam and Isbell 2002)
    • Individuals in trees begin a visual scan of the surrounding area
      • Rarely will vervets descend a tree and flee in response to an alarm call
    • Individuals on the ground flee to tree cover and begin a visual scan of the surrounding area
    • Responses may be habitat specific (Enstam and Isbell 2002)
• Intragroup calls (see complete list in Struhsaker 1967c)
  • Chutter
    • Low pitched, staccato-like call
    • Mouth closed or only partially open; teeth not exposed
    • Given by juveniles and adult females
    • Possibly to display aggression or solicit aid from other group members
  • Squeal and scream
    • Shrill; high pitched and uniform sounds
    • Possibly defensive calls or to solicit aid from other group members
  • Bark
    • Uncommon; used by adult and subadult males in agonistic encounters
  • Lip smack and teeth chatter
    • Rapid, slapping together of the upper and lower lips or teeth; teeth not conspicuously exposed
    • Performed by all sex and age classes, except infants
      • Audible to c. 9 m (c. 30 ft)
    • Possibly indicates nonaggression
  • Purr
    • In play, when juveniles wrestle and grapple with one another
    • Low frequency, thus rarely heard
• Other sounds (from Struhsaker 1967c unless otherwise noted)
  • Various sounds used during encounters with other groups
    • Some similar to intragroup calls; chutter, chirp, and bark
  • Infants make numerous sounds when separated from their mothers
  • Cough, sneeze, and vomit
• Click here for audio of vervet calls

Olfaction/Scent Marking

• Scent marking possible, requires more study(Isbell and Enstam-Jaffe 2013; Freeman et al. 2012)
  • Skin secretions and tissues from the sternal region need examination (Freeman et al. 2012)
  • Chest rubbing reported in some populations (Isbell and Enstam-Jaffe 2013)
    • Males and females rub their chests on trees, though females do so infrequently
      • Males chest rub 4.5 times more often as females
      • Frequency increases during the mating season
    • Stereotyped behavior (Freeman et al. 2012)
      • Stand bipedally on or by a tree trunk or branch
      • Embrace tree with both arms and rub chest repeatedly; throat and cheek less frequently
      • Stop frequently to inspect the area with the nose before continuing to rub
    • Higher-ranking males tend to chest-rub more than lower-ranking males

Displays

• Similar to other cercopithecines
• Bodily displays
  • Sideward display, sideward jerking of forequarters, lateral shaking of the head, head flagging
• Facial displays
  • Yawn
• Male specific displays of dominance (Isbell and Enstam-Jaffe 2013)
  • Red, White, and Blue display (Struhsaker 1967b)
    • Name derived from the characteristic red, white, and blue colors of the male's genital region (see above description of sexual dimorphism)
    • Male paces back and forth in front of subordinate; tail held vertically erect to expose brightly colored anus and scrotum
    • Subordinate often sits, crouched or hunched, and vocalizes
    • Display frequency peaks during mating season
  • Penile display (Struhsaker 1967b)
    • Male stands bipedally and directs his inguinal region toward the face of a seated male
    • Shoulders of seated male are grasped
    • Duration: 2-5 seconds
      • Followed by grooming at times

Walk slowly to forage (from Struhsaker 1967b,e unless otherwise noted)

• Gait symmetric
  • Right forelimb moves forward with left hindlimb
• Tail held straight down or arched over the back

Run/gallop quickly (from Struhsaker 1967b,e unless otherwise noted)

• Often to move across open, short-grass areas
• Gait asymmetric
  • Front legs move forward in unison, hind legs follow together meeting the forelegs on the ground beneath the mid-point of the body
  • Hops sporadically between strides
• Tail held erect or horizontal with the ground

Climb (from Struhsaker 1967e unless otherwise noted)

• Ascend trees head first
• Descend either head or tail first
  • Tail-first descent commonly used on vertical surfaces
  • Head-first descent commonly used on angled surfaces
• Tail acts as a balance or brace (when pressed against a tree branch or trunk)

Leap through trees

• Adult and subadult males sometimes run and leap through trees (from Struhsaker 1967d)
• Ricocheting off branches during intergroup encounters

Competitors (from Struhsaker 1967a unless otherwise noted)

• Insectivorous birds
• Herbivores; may feed on the same grasses, acacia seeds, and herbs
  • Waterbuck, lesser Kudu, and impala
  • Elephants compete for food and knock down vervet monkey sleeping trees while foraging
• Other omnivores
  • Baboons; compete for many plant and animal foods

Baldellou and Henzi (1992)
Cheney and Seyfarth (1983)
Cheney and Seyfarth (1987)
Cheney and Seyfarth (1989)
Enstam and Isbell (2002)
Fagan (2002)
Fairbanks (1990)
Fairbanks (2002)
Freeman (2012)
Freeman et al. (2012)
Fruteau et al. (2011)
Isbell and Enstam-Jaffe (2013)
Isbell and Pruetz (1998)
Isbell and Young (1993)
Isbell et al. (1998b)
Isbell et al. (2002)
Lancaster (1971)
Lycett and Henzi (1992)
Pasternak et al. (2013)
Pellis et al. (2014)
Struhsaker (1967a,b,c,d,e)