Pygmy Marmoset "Callithrix Pygmaea"
SOCIAL ORGANIZATION AND BEHAVIOR
Groups of pygmy marmosets range in size from two to nine individuals, but average group size is five. Solitarily ranging individuals of both sexes are also seen.
Most troops are composed of one dominant, reproductive female, a reproductive male, and the offspring from one to four litters.
Groups may also contain additional adult males or females that are unrelated to the reproductive female, but neither reproduce.
The reproductive female is dominant over all group members, the breeding male is dominant over all males in the group, and, among the offspring, the older siblings are dominant over the younger siblings except for dependent infants, that are not part of the dominance hierarchy.
Dominance can be assessed by which animals displace others at gum feeding sites; dominant animals supplant subordinate individuals.
Daily social behaviors observed among pygmy marmosets include grooming, huddling, and play. Grooming is seen during resting bouts throughout the day and while subadult females groom the dominant female more than vice versa, patterns of grooming between opposite sexes are not discernible.
Huddling is another social activity among pygmy marmosets in which group members remain in close contact during rest. Play is seen mostly among the subadults, juveniles, and infants and can be either solitary or social. Social play is usually chasing or rough-and-tumble play within groups of two or three individuals.
Young pygmy marmosets play during resting bouts in the late morning and early afternoon.
Group size fluctuates as subadult males and females disperse from their natal groups or unrelated adult males and females emigrate from the group.
Subadults become peripheralized over a gradual period of time, being ousted from their group's primary exudate tree and forced to feed in other areas.
During this time period, if the subadult tries to feed in the primary tree, their youngest siblings harass them and may displace them at feeding holes.
As this process continues, subadults make increasingly longer forays from their natal group and being to emit calls in an effort to locate a mate.
The dominant reproductive female may become intolerant and especially aggressive toward the end of her pregnancy and this may be a cue for the subadult pygmy marmosets in the group to begin dispersing (Soini 1988).
As is seen in other species, pygmy marmoset groups generally have only one dominant breeding female while other adult and subadult females remain in the group without breeding and help raise the offspring of the dominant female.
Rather than beginning to mate when they reach puberty, young pygmy marmoset females are reproductively suppressed when they remain in their.
In Ecuador, de la Torre et al. reported on one group that appeared to have two breeding females, but this is not generally seen (2000).
There is very limited data on age of reproductive maturity, but female captive pygmy marmosets reach sexual maturity between 15 and 17 months of age and if the young female remains in her natal group, fertility is suppressed through interactions with the dominant breeding female, her mother.
There is some evidence that young females exhibit ovarian cycles while living in their natal groups, but they do not reproduce as long as there is a resident dominant female.
If the breeding female ceases to reproduce or disappears from the group, her oldest daughter will become the next dominant female, often breeding with her father. In captivity, when more than one female gives birth, the offspring of the younger female are often victims of neglect or in fanticide by other group members.
Males are thought to reach sexual maturity around 16 months (Soini 1988).
Adult males in the group are interested in mating with the dominant female throughout the year, but the breeding female is not receptive to these advances during pregnancy or during the three to six weeks after parturition.
The dominant male aggressively intervenes between any males attempting to mate with the dominant female.
Some courtship behaviors exhibited by males include approaching and following the female, strutting, tongue-flicking, sniffing and licking the female's urine, scent marking using glands on the chest and around the anus and genitals, huddling, and grooming.
Females respond to these behaviors by presenting their genitals to the male, raising their tails into an arch position, scent marking, huddling, and grooming.
Pygmy marmosets do not exhibit birth seasonality but there are two birth peaks during the year, in the months of May and June and again between November and January.
Females can produce two litters each year and give birth to twins about 70% of the time in the wild. In captivity, twins are born 76% of the time, 16% of births are singletons, and triplets are seen in 8% of the births but do not generally survive lasts 141 days and the interbirth interval is, on average, between five and seven months
All members of a pygmy marmoset group take some part in rearing the offspring of the dominant female.
This greatly contributes to the survivability among wild pygmy marmosets which have a 67% rate of survival to the sixth month of life. Nearly 80% of total mortality in pygmy marmosets occurs within the first two months of life.
Infants are carried constantly for the first one to two weeks of life, but after this, a relatively unusual primate behavior is seen.
Parents deposit two-week-old infants in specific, relatively protected places and leave them there for increasing longer time periods while the adults forage in the vicinity.
The most common places that infant pygmy marmosets are left include the crown of the group's principal feeding tree or of another large tree in the group's home range.
This system of "baby-parking" is probably a way to decrease the cost of infant care which can include energetic costs of carrying the quickly growing infants, increased predator vigilance which distracts from feeding, and lost foraging opportunities because of decreased daily path length.
Additionally, infants that are parked rather than traveling on the backs of other group members or moving around freely are less vulnerable to predation by birds of prey.
When infants younger than two months are not parked in a tree, they are constantly being carried by one of the group members, with the oldest siblings (both male and female) doing a large majority of the carrying during this time.
From age two to five months, the infants start to move independently and are weaned by the end of the third month.
Weaning begins as early as eight weeks, around the same time that infants begin to feed independently from already-gouged exudate holes.
They do not begin to gouge their own feeding holes until much later in development.
From the age of six to 12 months, pygmy marmosets are considered juveniles and it is during this phase that the dominant female is likely to have another litter.
Infant carrying in juveniles is seen starting at six months and they become completely independent feeders, gouging exudate holes and feeding from them.
They enter the subadult stage from 12 to 18 months in which the only physical characteristics that differ from adults are their smaller body and genital sizes.
Throughout this time of development, play behavior takes up a considerable part of the day. Pygmy marmoset infants, juveniles, and subadults either play solitarily by exploring, hanging, leaping, running, and imitating others or in groups by chasing and tumbling with others.
By 18 months, they are virtually indistinguishable from adults of any other age.
Visual displays by pygmy marmosets are used in situations of threat, in order to convey dominance status, and reproductive status.
Mobbing behavior involves elaborate posturing and displays such as strutting, stereotypic, jerky movements, body swaying, and piloerection.
Groups of pygmy marmosets may mob animals such as birds, monkeys, squirrels, snakes, and human observers, if they feel threatened.
Mobbing also includes a genital display, seen in multiple other contexts. In the genital display, a pygmy marmoset of either sex turns its back to the observer, arches its back, raises its tail in a stiff arch, and the body and tail hair are ruffled.
This is seen in dominance interactions, where the more dominant individual displays to the subordinate, in intergroup encounters as a form of territorial defense, and in sexual solicitation.
Other types of communication among pygmy marmosets are chemical and vocal signals.
There are three important calls used by pygmy marmosets: "trills," "J-calls," and "long calls" "Trills" are used when feeding on exudates, foraging for insects, or traveling in proximity and are usually given between animals that are no more than five meters (16.4 ft) apart. "J-calls" are comprised of a series of notes quickly repeated by the caller and are heard when animals are between five and 10 meters (16.4 and 32.8 ft) of each other during short-distance locomotion. Both "trills" and "J-calls" serve to mediate interactions between group members and to maintain short-range contact throughout the day and are heard frequently.
The "long call" is heard during travel and in response to hearing calls from other groups and is given when pygmy marmosets are spread out over distances greater than 10 meters (32.8 ft).
This is often used by single pygmy marmosets calling for a mate. It is made up of repeated, high-pitched, long notes that sound like "kwee-kwee-kwee...".
Pygmy marmosets use scent in chemical communication, rubbing the scent glands found on their chest and around their anus and genitals on a surface and leaving a mark for others to smell.
Smell is important to New World monkeys because of their specialized second nose, or vomeronasal organ, which allows them to be especially in tune with chemical cues in the environment.
Female pygmy marmosets use chemical communication to convey reproductive status to males.
During periods of peak fertility, females do not alter the amount or type of scent-marking behavior, but males are able to discern the reproductive state from the marks left on surfaces.
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