Common marmoset

The common marmoset's claw-like nails, incisor shape, and gut specialization reflect their unique diet, which is primarily made of plant exudates and insects. Common marmosets feed on gum, sap, latex, and resin.[12][14] They use their nails to cling to the side of a tree, and with their long lower incisors, chew a hole in the tree.[15] The marmoset then licks up the exudates or swoops them with the teeth.[16] From 20 to 70% of the marmoset’s feeding behavior includes eating exudates.[9][15]

Exudates provide marmosets with a reliable food source in their seasonal habitat. They rely on these foods particularly between January and April, when fruit is not abundant. A marmoset may visit a tree hole multiple times, including those made by other animals. In addition to exudates, insects also prove an important food source for marmosets, making up 24-30% of their food. The small size of marmosets allows them to stalk and ambush them.[14] Marmosets also eat fruits, seeds, flowers, fungi, nectar, snails, lizards, tree frogs, bird eggs, nestlings, and infant mammals.[16] Marmosets may compete for fruit with birds, such as parrots and toucans, and with woolly opossums.[16]

Two marmosets

Common marmosets live in stable extended families, with only a few members allowed to breed.[17][18] A marmoset group can contain as many as 15 members, but a more typical number is nine.[16] A marmoset family usually contains one or two breeding females, a breeding male, their offspring, and their adult relatives, be they their parents or siblings.[18] The females in a group tend to be closely related, and males less so. Males do not mate with breeding females to which they are related. Marmosets may leave their natal groups when they become adults, in contrast to other primate species, which leave at adolescence. Not much is known of the reasons marmosets leave their natal groups.[18] Family groups fuse into new groups when a breeding male dies.[19] Within the family groups, the breeding individuals tend to be more dominant. The breeding male and female tend to share dominance. Between two breeding females, though, one is more dominant. In addition, the subordinate female is usually the daughter of the dominant one. For the other members, social rank is based on age.[17] Dominance is maintained though various behaviors, postures, and vocalizations, and subordinates groom their superiors.[17]

Mother and baby at Forte da Ponta da Vigia, Brazil

Common marmosets have a complex mating system. They were thought to be monogamous, but both polygamy and polyandry have been observed.[17] Nevertheless, most matings are monogamous. Even in groups with two breeding females, the subordinate female often mates with males from other groups. Subordinate females usually do not give birth to fit offspring.[20] Mating with extra-group males may allow the female to find potential mates in the future. Females that mate successfully but lose their young move to other groups and may gain dominant breeding positions.[20]

Common marmoset found in a Pernambuco resort

The breeding individuals in a group need the other members to help raise their young. Thus, the pair behaviorally and physiologically suppresses the reproduction of the other members of the group.[21][22] Since these suppressed individuals are likely related to the breeding pair, they have an incentive to care for the young, as they share genes with them.[22] In addition, the presence of a related male affects female ovulation. Female ovulation does not occur when their fathers are around, but does occur when an unrelated male is nearby, instead. They also display aggressive behavior towards their mothers,[22] possibly to displace them.

When conditions are right for them to breed, adult females breed regularly for the rest of their lives. Females flick their tongues at males to solicit mating. The gestation period lasts for 5 months, and females are ready to breed again around 10 days after giving birth. Five months pass between each parturition, so they can give birth twice a year.[16] Marmosets commonly give birth to nonidentical twins. Because of this, females are under stress during pregnancy and lactation, and need help from the other members of the family.[12][16] Infant marmosets instinctively cling to their mother's back and do not voluntarily let go for the first two weeks. After that, they become very active and explore their environment.[16] The breeding male (likely the father) begins handling the twins, and all members of the family care for them.[23] In the following weeks, the young spend less time on their mother's back and more time moving around and playing.[16] Infants are weaned at 3 months. At 5 months, they enter their juvenile stage, when they have more interactions with family members other than their parents, and rough play helps to establish their future status. Another set of infants may be born and the previous young carry and play with them.[23] Marmosets become subadults between 9 and 14 months old, act like adults, and go through puberty. At 15 months, they reach adult size and are sexually mature, but cannot breed until they are dominant.[23]

Common marmoset at the Erlebnis-Zoo Hannover

Common marmosets employ a number of vocal and visual communications. To signal alarm, aggression, and submission, marmosets use the "partially open mouth stare", "frown", and "slit-stare", respectively. To display fear or submission, marmosets flatten their ear tufts close to their heads.[16] Marmosets have two alarm calls - a series of repeating calls that get higher with each call, known as "staccatos", and short, trickling calls given either intermittently or repeatedly, called "tsiks". Marmoset alarm calls tend to be short and high-pitched.[19] Marmosets monitor and locate group members with vibrato-like, low-pitched, generic calls called "trills".[24] Marmosets also employ "phees", which are whistle-like, generic calls. These serve to attract mates, keep groups together, defend territories, and locate missing group members.[24] Marmosets use scent glands on their chests and anogenital regions to mark objects. These are meant to communicate social and reproductive status.[16]