Geoffroy's Marmoset

Geoffroy's marmoset, also called the white-headed or tufted-ear marmoset, is a small primate endemic to forests in eastern Brazil. Its native range covers the states of Bahia, Espírito Santo and Minas Gerais, and it has also been introduced to Santa Catarina. In Brazil it is known as the sagüi or sauim. Its diet consists of fruits, insects and the gum of trees. It is recorded as a host of Pachysentis lenti, an intestinal parasite belonging to the acanthocephalans.

About the Geoffroy's marmoset

Geoffroy's marmoset, also called the white-headed or tufted-ear marmoset, is a small New World monkey of the family Callitrichidae that lives in the Atlantic forests of eastern Brazil. It is one of six Atlantic marmosets in the genus Callithrix and feeds on fruit, insects and gum it gnaws from tree bark.

Its scientific name is Callithrix geoffroyi. It was once treated as a subspecies of the common marmoset, Callithrix jacchus, and was declared a separate species in 1988. It shares its genus with the other Atlantic marmosets, such as the black-tufted, Wied's and buffy-headed marmosets.

This is a very small primate. The head and body measure only about 20 cm (7.8 in), and the tail adds another 29 cm (11.4 in). Males are larger, weighing 230 to 350 g (8 to 12 oz), while females average about 190 g (6.7 oz). The body is dark or blackish brown, and the long tail is ringed with gray and black bands. Adults have a striking white face: white forehead, cheeks, temples and throat, set off by tufts of black fur in front of the ears.

Babies look different. Juveniles lack both the ear tufts and the white face. The tufts start growing at about two weeks old, and a young marmoset has full adult markings by about five months.

Like other marmosets, Geoffroy's marmoset has claws instead of nails, thumbs that are not opposable, and sensitive tactile hairs on its wrists. Its tail is used for balance and communication, not for grasping. The lower incisors are long and bent, which lets it chew holes in bark to reach gum.

Behavior and diet

Geoffroy's marmosets are diurnal tree dwellers that climb and cling to trunks with ease. They live in family groups of 8 to 10 animals that defend a home range of 10 to 40 hectares (25 to 100 acres).

How they spend the day depends on the season. In the wet season, one study found them resting 32% of the time, feeding 21%, moving 20%, foraging 14% and gouging bark for gum 13%. The remaining few percent went to playing, grooming, scent marking and calling. In the dry season, resting drops to about 18% and foraging rises to about 21%.

What they eat

The diet is mostly fruit, insects and plant gums. They also eat flowers, nectar, frogs, snails, lizards and spiders. Gum is a staple. Using those specialized lower teeth, they gouge into tree trunks, branches and vines so the sap seeps out, a habit known as tree-gouging. Marmosets in general center their territories on the trees they tap this way.

Geoffroy's marmosets have also been reported following swarms of army ants to snap up insects the ants flush out.

Watching for danger

Small primates like these are heavily preyed on, and members of the marmoset family may be affected by predation more than any other primates. Raptors, snakes and wild cats all hunt them. Groups stay vigilant, take turns at the best lookout spot, and give alarm calls when a threat appears. Depending on the predator, they may watch it, mob it, flee or freeze. When danger passes, they groom one another, which seems to help calm the group.

Family life

Each group has a single breeding pair, a dominant male and female bonded to each other. The dominant female's behavior stops ovulation in the other females, possibly helped by scent from her glands, so subordinate females cannot breed while they stay in the group. Usually only one male mates with her, although polyandry, rare in mammals, has been observed.

Breeding happens year-round. Pregnancy lasts 140 to 148 days, and there are usually 150 to 152 days between births. Twins are typical, though singletons and triplets occur. The father helps at the birth, licking the newborns before passing them to the mother, and for the first week he carries the babies exclusively. After that he remains the main carrier, but the whole family pitches in. Older siblings help raise younger ones, learning skills they will need for their own young.

The mother nurses both twins at once. Young are weaned at 5 or 6 months and reach maturity at 15 to 18 months. Geoffroy's marmosets generally live about 10 years.

Range and habitat

Geoffroy's marmoset is found only in eastern Brazil, where it is native to Bahia, Espírito Santo and Minas Gerais. It has also been introduced to Santa Catarina in the south. Within the native range it occurs north to the Rio Jequitinhonha, and the population south of that river descends from animals released near its mouth in 1975. A hybrid population of Geoffroy's and black-tufted marmosets has been found in the Serra da Piedade.

It lives in the Atlantic forest, in secondary lowland and sub-montane forest, evergreen and semi-deciduous forest, forest edges and patches of dry forest. It is generally found at about 500 to 700 m (1,640 to 2,300 ft) above sea level, and occasionally as high as 800 m (2,625 ft).

Conservation status

Geoffroy's marmoset is listed as Least Concern on the IUCN Red List, most recently assessed in 2021, and its population trend has been classed as stable.

That listing has shifted over time. In 1982 primatologist Russell Mittermeier recommended listing it as endangered, but studies in 1991 found it locally abundant, if patchy. The IUCN listed it as Vulnerable in 1994, 1996 and 2000 before it was downgraded.

Habitat loss remains the main pressure. The species once lived throughout the Brazilian Atlantic forest, but only about 1% to 5% of that forest remains, and less than 6.8% is left in Minas Gerais. Because Geoffroy's marmoset is still relatively abundant and occurs in many protected areas, its rate of decline is not considered enough for a threatened listing. It is occasionally captured for the pet trade.