At the Zoo: Miniature Monkeys
by Susan Lumpkin
Pygmy marmosets births are not uncommon events at the National Zoo. You can look for them in the Great Ape House and in the Small Mammal House. But it takes a real eye for detail to spot these infants, if, that is, you could first spot their diminutive mothers. Newborn pygmy marmosets weigh just about half an ounce and are less than two inches long, while their mothers top the scales at four or five ounces and reach perhaps six inches in length (not including their six- to nine-inch-long tails). To borrow the giant panda baby analogy, a mother pygmy marmoset weighs about as much as a stick of butter (albeit one with a long tail), while a baby makes a generous pat. Fluffy coats, however, make both look a bit bigger than that.
Native to the upper Amazon, pygmy marmosets (Callithrix pygmaea) are the smallest of South America's primates and rival a few prosimians such as bush babies and tarsiers for the title of smallest primate anywhere. Being tiny gives the pygmy marmoset at least one significant advantage over some of its larger relatives: People ignore them because they are too small to usefully hunt for food. This, combined with their habitat preferences, enables these monkeys to survive quite well in proximity to people.
The arboreal pygmy marmosets most often live in the trees at the naturally created edges of seasonally flooded forests, usually along a river. However, they are also found in the "unnatural" edges created when people clear forest for pastures, crop fields, and orchards. For these reasons, pygmy marmosets remain relatively common and are not considered to be in any immediate danger.
These marmosets eat spiders and insects, which are particularly abundant in edge habitats, supplemented with fruits and occasionally small vertebrates such as lizards. Grasshoppers are their favorite meal and to catch one a marmoset may even venture to the ground, something they are loath to do otherwise. Butterflies are another favorite. The marmosets stalk butterflies that are attracted by the monkey's primary source of nutrition: the exudates—gum and sap—of a variety of species of trees and vines. With chisel-shaped lower incisors, they gouge small holes into trunks, limbs, or stems to make the gum flow, then lick up small drops of the carbohydrate-rich liquid. Group members share a small home range—less than an acre in size—where one or a few trees may provide all the gum the group needs for several months or even a few years. When gum runs low, the group moves on to a new home range.
A typical pygmy marmoset group of seven to nine individuals includes a breeding female and her mate along with her offspring from as many as four or five litters of singles or twins. One or two of the young are usually infants being carried by their mother, father, or older sibling, while others may be nearing adulthood. As young mature into adults, they are slowly pushed out of the group, mostly by their mother, and eventually find home ranges and mates with which to start a new family group.
Several pairs or small groups of pygmy marmosets live at the Zoo. In the Small Mammal House, pygmy marmosets now inhabit four exhibit spaces, some in which they are the sole occupants and others they share. In the house's largest exhibit, the tiny monkeys live in the midst of pale-faced saki monkeys, golden lion tamarins, two-toed sloths, two kinds of armadillo, and an iguana.
The Great Ape House pair and their young live freely in the house's huge central planter, taking occasional forays off to other trees in the building. Reluctant to travel on the ground, the marmosets scamper across a ledge above the door to reach a ficus, and leap a few feet through the air to get to a nearby rubber tree. Provided with social companions, plentiful food, cozy nestboxes, and lots of trees, the marmosets apparently have no inclination to try to leave the Great Ape House. In fact, even in the wild, pygmy marmosets usually stay within a quite small area, dividing their time between a nighttime roosting tree and a daytime gum tree less than 100 feet away. Other activities, such a searching for insects, occur in between.
Mealworms, fruit, and a prepared "marmoset diet" make up most of the pygmy marmosets' Zoo daily menu. But to satisfy the monkeys' taste for gum—and to display their feeding adaptations to visitors—keepers also push gum arabic into small pre-drilled tree holes. The marmosets then gouge out and eat bits of the sticky food. Visitors watching carefully can also see them gnaw at the bark of the trees in their exhibits.
As they are in the wild, pygmy marmosets in the Zoo are active throughout the day. They are always fun to watch scurrying about the exhibit. They walk and run along the upper surfaces of branches as well as travel upside down on the undersides of horizontal limbs. Another unusual behavior to look for is head turning. A pygmy marmoset can turn its head 180 degrees to either side, enabling it to scan the surrounding scene for predators while clinging to vertical limbs and branches. When the monkey fully rotates its head, it looks as if it is on backwards!
The cold winter months are a great time to get to know the inhabitants of the Zoo's warm buildings. Why not start with these charming miniature monkeys?
(ZooGoer 24(1) 1995. Copyright 1995 Susan Lumpkin.
All rights reserved.)
