Equatorial Saki, Pithecia aequatorialis
EQUATORIAL SAKI
Pithecia aequatorialis
Geographic Distribution and Habitat
The equatorial saki (Pithecia aequatorialis), also called the red-bearded saki or Peruvian saki monkey, is a Latin American monkey. They live predominantly in Peru, ranging from the south of the Rio Napo and southeast side of the Rio Curaray to the right bank of the Rio Tigre in the west. Photo evidence suggests that they wander around the Ecuadorian border as well, and recent studies have confirmed their presence in the province of Pastaza.
The environment that equatorial sakis inhabit and its intricacies are a logistical nightmare. For example, the abundance of trees has hindered scientific research. Reaching the habitat of these creatures has always been an arduous task, and only recently have researchers managed to overcome such difficulties.
As a species that thrives in densely forested areas, the equatorial saki lives in wet forests that are seasonally flooded, as well as in moist forests not usually inundated by water. Their population is scattered across the territory that they inhabit; however, they occupy mature forests that offer a variety of fruit more abundantly.
Their distinctive calls suggest that the equatorial saki diverged long ago as a unique species. There are currently no recognized subspecies.
Size, Weight, and Lifespan
The equatorial saki is a relatively small monkey. The average saki measures about 15-17 inches (40-44 cm) and weighs 4.4-5.5 pounds (2-2.5 kg), with females being slightly smaller and more slender. This species has a thick non-prehensible tail, that is, a tail that can’t be used to grasp objects. The average tail length of male equatorial sakis is 18.2 inches (46.1 cm), while females have a slightly shorter tail, averaging 17.6 inches (44.8 cm). They live around 15 years.
Appearance
Males can be easily spotted not so much because of their size, but thanks to their distinctive color patterns. The equatorial saki has thick, black-grizzled fur streaked with grey and yellow. Males sport some flashy orange fluff around their chest area and have a black muzzle framed by white hair. Females also have distinctive orange chests, but much less showy. Where they differ the most is in the overall tone of their fur. Females tend to be greyer and the white hair that frames their muzzle is much less defined. Both sexes look pretty fluffy because their fur is not only thick but quite long too. Infant and juvenile equatorial sakis are similar to adults, with the exception of their heads, which tend to be much whiter than adults’.
Diet
The equatorial saki is a frugivorous species. They feed on the luscious fruit that grows in the Amazonian forest, which they bite into with their strong incisors and canines, perfectly adapted to break through tough fruit skin. They do not turn up their noses to the occasional seeds, leaves, nuts, and insects either, which they happily snack on as a supplement to their usually fruit-rich diet. Interestingly, related species of sakis have been seen eating mud sourced from termites’ mounds. This soil is processed by these insects and is exceptionally rich in carbon and clay. Because sakis eat a lot of unripe fruit, which can cause tummy aches and other gastrointestinal problems, they probably eat soil for medicinal purposes as the clay in it absorbs and gets rid of harmful substances.
Behavior and Lifestyle
The equatorial saki is an arboreal species, that is, they spend the majority of their time in the many trees that populate the Amazonian forest.
Trees offer great protection from predators. On the one hand, they can’t be climbed by many ground-dwelling animals; on the other hand, the canopy and branches of the trees shield them from potentially dangerous birds. The monkeys avoid predation by being quiet so that they can fly under the radar of peckish predators. Among these, we find harpy eagles, Harpia harpyja, and ocelots, Leopardus pardalis.
As a diurnal species, they sleep at night and are active during the day. They forage and socialize in the dense forest trees, traveling from one branch or tree to another by leaping, climbing, and walking on four limbs. Their home range is quite extensive, considering their smaller size, as it extends over 3.5 square miles (9 km2).
The equatorial saki lives in small groups containing few individuals, sometimes in pairs, either of the same or opposite sex. Smaller groups come together to form larger congregations that consist of multiple females and males. It is difficult to ascertain whether the individuals living in a group are blood-related or not because this species is so elusive. Given the more adventurous role that males take on when threatened by intruders, we can assume that their groups are male-dominated.
We know that the equatorial saki relies on vocal communication to maintain contact with other members of its group. Vocal communication acts as a form of social glue, helping equatorial sakis strengthen their social bonds through collaboration. Calls used for food gathering and mating serve this function, for example. Since dense forest environments impede visual signals, vocal communication remains the most effective method of interaction for animals that dwell in forested areas. Nevertheless, compared to other primate species, equatorial sakis are relatively quiet.
The equatorial saki has a rich repertoire of calls. At least eleven calls have been identified so far, with four call variations. They use whistles, chucks, trills, purrs, screams, and grunts to communicate. Their young also emit different calls, known as juvenile yip calls.
Unlike many primates, equatorial sakis are often quiet when they encounter predators, perhaps to increase their chances of survival, although we do not know for sure why they take a more taciturn approach to threats. On the other hand, males take on a leadership role by being more vocal than females when strangers approach their group; their calls are often followed by other intimidating tactics such as chasing.
Equatorial sakis are generally thought to be monogamous, meaning they typically mate with a single partner. However, some studies have challenged this belief, suggesting that monogamy may play a less significant role than previously thought. While sakis often form preferential partnerships, they occasionally mate with other individuals both within and outside their groups.
Equatorial sakis have flexible social structures. Females usually remain in their natal group throughout their lives, reproducing within this ‘safe haven.’ In contrast, males emigrate multiple times during their lives, often joining neighboring groups. They may even become part of groups or pairs where a resident male is already present, with both males cooperating in territorial defense. Males also take a proactive role in courtship and partner-seeking. Females typically give birth to a single infant after a gestation period of 150 to 180 days.
Newborns are helpless at birth and rely on their mothers for nursing and protection. Males also step up to raise their children: they groom and take care of their young.
Reforestation weighs on the equatorial saki’s tiny shoulders. This species feeds on fruit and help disperse seeds through their home range. It is definitely not an easy task, but they contribute immensely to counterbalance the negative effects of human activity. By spreading fruit seeds across their territory, they allow plants to grow in other areas.
Equatorial saki is classified as Least Concern by the International Union for Conservation of Nature (IUCN, 2015), appearing on the IUCN Red List of Threatened Species. While much remains unknown about their specific habitat preferences, the Amazonian forest they call home is threatened by deforestation. They are often victims of hunters and their coats and body parts are used as decorations or accessories (e.g., as hats) and they are often sold as pets. Humans, sadly, are their biggest threat.
Equatorial sakis are listed in Appendix II of the Convention on International Trade in Endangered Species (CITES), an international agreement between governments whose goal is to ensure that international trade in specimens of wild animals and plants does not threaten their survival.
The best way to keep their population stable and protect these animals is through education. Education efforts should focus on increasing understanding of these animals and their ecological roles, while also collaborating with local communities to raise awareness.
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Written by Mirko Cerrone, November 2024