Amazon Cruises and Neotropical Primates

One of the most sought-out life forms on our Amazon travel are the monkeys. The Amazon rainforest has many species in a range of sizes and show great variation in color patterns and behavior. During our skiff rides along the rivers, the embankments are prime locations for sighting these fascinating primates. There are several differences between “Old World” monkeys and “New World” monkeys, the primary being the position of the nostrils on the face. Old World monkeys, as all humans, have downward-pointing noses whereas New World monkeys have nostrils that point out to the sides. All New World monkeys are arboreal, and have no species similar to the Old World baboon which stay on the ground and prefer open savannas. The long tails of the New World monkeys range in lengths and function, and not all are prehensile.

Marmosets (Callathris, Cebuella) and tamarins (Saguinus, Leontopithecus) are distinguished from other new world monkeys by their incredibly small size; they all have long, non-prehensile tails; their hands and feet have claws and not nails as in the majority of neotropical monkeys (the one exception are the thumbs, which do indeed have a nail and not claw); The main difference between the two is found in the jaw and teeth: marmoset jaws and teeth are adapted to biting into the barks of trees in order to form small holes where sap will collect, becoming what can be termed “Sap-suckers;” Although Tamarines will steal sap from the marmoset-made holes, their teeth and jaws are not adapted to the chewing and biting necessary to make them. Both tamarins and marmosets also feed on fruits and insects. Both demonstrate a polyandrous social structure and the young are usually carried on the back of males. This is understandable since the females frequently give birth to twins instead of a single young, and with their mobile lifestyle could not possibly carry both young. Tamarins and marmosets easily adapt to secondary growth and disturbed forest because of the profusion of tangled vines and trees which they prefer, but can also inhabit primary forest along riverbanks where the vegetation is also thick.

Saddleback tamarin (Saguinus fuscicollis). There are 13 subspecies in the Amazon; two forms are found in the area of the Marañon River: north of the river the saddleback tamarin has distinct reddish forequarters, whereas south of the Marañón the saddleback tamarins sport black forequarters. We will be visiting both sides of the Marañón on our Amazon cruise, so sightings of both forms are a real possibility. These are the most commonly seen tamarins in Peru, found in middle and lower levels of the forest. They forage for insects primarily, but also drink nectar from flowers, steal sap from marmosets, and eat fruits. When moving from one location to another, acrobatic leaps from branches are common. They are very active monkeys and live in groups of anywhere from 2 to 20 of related individuals. They are polyandrous and practice cooperative breeding (one female will mate with several males) and females usually have twins. Non-breeding individuals will help with the care of the young; a good demonstration of kin selection where it is better to help raise half-siblings (or full) than nothing. Oftentimes when we are searching the riverbanks on our Amazon cruise, these small primates give themselves away by their bird-like trills and whistles.

Pygmy marmoset (Cebuella pygmaea); the tiniest Neotropical monkey, from French “marmouset” meaning “small boy.” These small primates are territorial with a rather small range; they will tend a tree they have prepared with small holes for sap collection (therefore called “sap-suckers”), which they will then visit daily. They supplement their sap diet with berries, buds, fruit (including bananas), and arthropods. They live in relatively small family groups of two to six individuals. Their preference is for seasonally-flooded forest and riversides, and are rarely, if ever found on terra firme.

Cebidae (Callicebus, Cebus, Lagothrix, Pithecia, Samiri, Alouatta, Ateles, Aotus)
These monkeys have nails (not claws) on all digits and five toes on all feet. On spider monkeys, the hands have only four functional digits (vestigial thumbs). The heaviest species have prehensile tails whereas the lighter species do not; they are all arboreal; females give birth to only one young which is carried by the female for the most part, however in small species who display monogamous behavior, the males help carry the young as well. Their general food preferences are for fruit, insects, and leaves (some species eating more leaves than fruit). There is considerable geographic color variation in species separated by mountains or rivers; 11 genera, 31 species, not closely related and with very different ecologies. 

Small monkeys around 1 kg.
Night monkey (Aotus spp), also known as “douroucouli” from a South American Indian name or “owl monkey.” Around 1 kg / 2 lbs; only genuine nocturnal monkey on Earth. They eat fruits, insects, and nectar and roam in the upper half of the forest canopy. Monogamous, with the males carrying the young; generally quiet and sedentary, they will stay in the same tree for hours. During the day they gather in tree holes all together, preferring thick vegetated areas often found near riversides. Night monkeys are very flexible in their distribution, found in primary forests as well as secondary and disturbed areas. They live in the wettest to driest regions of the South American tropics. As a possible adapt to nighttime and low-light, they communicate by body language rather than facial expression and have no color vision (“monochromats” - unusual among the New World monkeys). They have a better spatial resolution at low light levels than other primates which contributes to their ability to capture insects and move at night. Night monkeys make a notably wide variety of vocal sounds, with up to eight categories of distinct calls (gruff grunts, resonant grunts, screams, low trills, moans, gulps, sneeze grunts, and hoots).

Dusky titi monkey (Callicebus moloch); this species is diurnal (active only during daylight hours) and is considered the only folivorous small monkey. This means it eats exclusively leaves and fruits with a particular enjoyment of bamboo; it prefers areas of dense vegetation (as along riversides and the varzéa regions). Because of this diet, it spends long periods of relative inactivity during the day, and can hide for hours. Pairs are monogamous, and males carry the young. Morning duets are a giveaway for their location. Dusky titi monkeys have no prehensile tails and in the forest are not leapers and bounders.

Common squirrel monkey (Saimiri sciureus); these monkeys are diurnal, arboreal, and live in large groups of 20+ members; they eat insects, fruits, and nectar. They are small, slender and agile, preferring areas of vine and thick vegetation (rivers and lake edges, varzéa); rare in areas far from water. They are very active and sometimes spend time on the ground when foraging, and are often associated with brown capuchin monkeys.

Medium monkeys between 2-4 kg, have weakly prehensile tails with hairy undersides – not used for hanging. These monkeys eat primarily fruits, invertebrates, and small vertebrates.

Brown capuchin monkey (Cebus paella); diurnal and arboreal, they live in groups of 5-20 individuals. They eat ripe fruits, palm nuts, arthropods and small vertebrates; forage middle-low layers in forest and are renowned for their tendency to tear apart vegetation and eat anything they can find (from baby squirrels to bird eggs to lizards). Quite noisy, they are common in their range. These monkeys are strong and can break palm nuts by banging them on branches.

White-fronted capuchin monkey (Cebus albifrons); diurnal and arboreal, they move in groups of 7-30 individuals, feeding mainly on fruits, seeds, arthropods (especially wasps); they use all levels of the forest including the ground; less destructive than brown capuchin monkeys, they are quicker, lighter, and show more agility.

Monk saki monkey (Pithecia monachus); diurnal and arboreal, they travel in groups of 2-8 individuals; bushy non-prehensile tails, body covered by shaggy hair. These monkeys stand out from others by their divergent upper and lower canines which push the mouth into frown; the teeth are used to split unripe fruit for the seeds inside; also eats leaves and ants. They are found primarily in middle-level and upper forest; shy and quiet, there is only one breeding female in a group who gives birth every 2-3 years. They are found in both terra firme and varzéa habitats.

Large monkeys of 4 kg+; all these species have strongly prehensile tails with bare skin on the underside gripping surface of the tail tip; they eat primarily fruits and leaves, and are considered exceptionally important seed dispersers in the rainforest.

Red howler (Alouatta seniculus); this is the only large red and gold prehensile-tailed monkey species. They can be heard roaring and howling at dawn, at dusk, and at approaching rainstorms. They are diurnal and arboreal moving in groups of 3-9 individuals. They eat fruits and leaves, and are generally quiet and slow-moving with small home ranges. Often when walking through a rainforest, their presence is noticeable by a strong stable-like smell. This is because of their tendency to stay in one location for a fair amount of time; their droppings accumulate below the trees. Howler monkeys are known for their defensive defecation and urination on people if they stand around too long. On our Amazon cruise they can be spotted from the skiffs high in riverside trees. Because howler monkeys generally inhabit small home ranges, they can survive in fragmented forest where others cannot.

Common woolly monkey (Lagothrix lagothricha); diurnal and arboreal, they live in groups of 2-60 (larger numbers in areas they are not hunted). Within these larger groups, they are often in family units of 3-9 individuals which sleep together at night. They eat ripe fruits, seeds, palm nuts, leaves and arthropods. They generally move in the upper and middle levels of the forest. Woolly monkeys have a slow reproduction, with females maturing around 3-8 years old, giving birth every other year. This species is not found in secondary forest, but can be found in both terra firme & varzéa. They are intensively hunted for their meat (considered the best) and so are considered highly endangered.

Black-faced black spider monkey (Ateles paniscus chamek); this species has two forms, with the red-faced A.p.paniscus found east of the Rio Negro and north of the Amazon River. These are extremely long-limbed monkeys that swing from branches, and with a prehensile tail so well-adapted that the skins on the underside are as unique to the individual as a fingerprint. Their hands have only vestigial thumbs which are an adaptation for grasping branches more easily when moving quickly through the canopy. They are diurnal and arboreal, spending time in social groups of up to 20 individuals broken down into smaller family groups of 1 to 5 members. They use the upper level of trees in tall, open forest and can be hard to spot when quiet and sitting or laying without movement. They have a very slow reproductive rate, with females giving birth every 3 to 4 years, and not reaching sexual maturity until 4 or 5 years of age. They are found almost exclusively in tall, undisturbed rainforest, so
 tour the Amazon with us to explore!

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