The black howler monkey or saraguato monkey ( Alouatta palliata ) is a tropical primate of the Atelidae family and the Alouattinae subfamily. This subfamily includes only the genus Alouatta . FIt is part of the platyrhine monkeys of the new world.
Within the genus Alouatta at least nine species are recognized because taxonomic disagreements still exist within this group of primates. In turn, five subspecies are recognized within Alouatta palliata which are: A. p. palliata , A. p. mexicana , A. p. aequatorialis , A. p. coibensis and A. p. trabeata .
These monkeys are essentially daytime activities. At dawn, males begin to emit loud vocalizations because the hyoid bone is highly developed and acts as a sounding board.
During this time, the temperature gradients in and above the forest create the necessary conditions for sound to travel great distances in the lower canopy. The howl of these tropical monkeys reaches up to 90 decibels.
Also, the groups transmit their location information as a form of remote communication so as not to conflict. In addition, with these howls they delimit the territory of action of each group during their daily activities.
The distance between groups is apparently estimated by the intensity with which the howls arrive between groups. These monkeys have varied social behaviors in response to reproductive stimuli, stress and as defense methods.
Howler monkeys like other primate species are very efficient at dispersing seeds in the habitats they occupy. The fragmentation of habitats resulting from deforestation and the decline in populations of these mammals have ecological consequences at all levels.
Black howler monkeys are among the largest and largest primates in the Neotropics. The average length of these monkeys, not including the tail, is approximately 56 centimeters for males and 52 cm for females.
On the other hand, the length of the tail is quite variable, reaching between 55 and 65 cm, with males having their tails a little shorter than that of females. The prehensile surface of the tail is hairless and has a robust pad for easy grip.
There is an evident sexual dimorphism as the males are more robust, weighing between 4.5 and 10 kg, while the females weigh between 3 and 7.6 kg.
The coloration of these animals is mainly black, although the region of the sides and shoulders have a brown or slightly blonde coloration. Like other species of the genus, the hyoid bone located below the root of the tongue and above the larynx is highly developed and forms a kind of bulge in the throat.
Habitat and distribution
Black howler monkeys have a wide distribution in the Neotropics, from Central to South America.
In Central America they are found in Mexico (Veracruz, Campeche, Chiapas, Tabasco and Oaxaca), Guatemala, Honduras, Nicaragua, Costa Rica and Panama. While in South America they occupy western Colombia, Ecuador and Peru towards the Pacific coast.
Howler monkeys occupy a wide variety of humid forests to semi-deciduous forests on mountain slopes. However, they are less related to floodplain environments than other species of the genus, for example, Alouatta seniculus .
This species mainly occupies lowland evergreen forests, but can also be found in mangroves, dry forests, deciduous forests, riparian forests, as well as secondary and subxeric forests.
Within these wooded habitats, howler monkeys move in the middle and upper levels of the canopy. In addition, to move between arboreal matrices or in search of water in the dry season they can easily go down to the ground.
Black howler monkeys have a wide distribution in Central and South America, which is why they have been included in the category of least concern according to the IUCN.
However, some countries such as Colombia classify the species as vulnerable (VU), with hunting and the destruction of natural habitats the main problems that have affected their populations. The species is also listed in Appendix I of CITES.
Fortunately, Alouatta palliata occurs in several national parks throughout its ranges. However, the fragmentation of natural ecosystems and the isolation of groups are strong threats for this species in the future.
The latter is of great importance for the long-term conservation of the species. The only intervened systems that have the presence of this species are those that conserve trees of the Moraceae, Leguminosae, Anacardiaceae, Annonaceae families among others, which are an important source of leaves and fruits.
In some areas it has been documented that a decrease in the populations of these primates, and consequently in the production of manure, has caused decreases in the abundance and diversity of dung beetles.
The dominant male of the group is the only one that copulates with the females. Males reach sexual maturity after they are four years old while females mature after three years.
The action of various sex hormones indicates to males the reproductive status of females. Males are often observed monitoring female genitalia and testing female urine. The fertile cycle of the female lasts approximately 16 days in which she mates several times with the dominant male.
Gestation lasts approximately 186 days and there is no specific time of birth, so mating can occur throughout the year. When these monkeys are in habitats with a marked seasonality, the females usually synchronize their reproductive cycles.
The female usually gives birth to a single young whose tail is not functional. During the first two or three weeks after birth, the young are held by the mother’s womb and after this period they migrate towards the back.
Young calves are highly dependent on the mother for the first month, then they begin to experience some independence without straying too far from the mothers.
The care of the young takes about 18 months when the juveniles are weaned and the female prepares for a new reproductive event that occurs 2 to 3 years after the birth of a young.
In general, the mothers avoid that other members of the group, mainly young females interested in the young, have contact with them during the first months. These females are perceived as a threat and are chased away by the mother with aggressive behaviors.
When the young are relatively independent, interactions with other members of the group are more frequent. On the other hand, generally the proportion of female offspring that survive to the first year is higher than that of males.
The reproductive performance of each group depends essentially on the behavior of the dominant male, as well as the proportion of juveniles and adults within each group.
The protective role of males against predators found in the canopy, such as the harpy eagle and some felines affects the growth rates of each group. Likewise, aggressive behaviors specific to group members and competition for resources determine the group’s growth structure.
These monkeys are primarily herbivores. The diet is mainly made up of leaves and fruits. During the flowering season, they are also observed consuming flowers. Around 48% of the volume consumed is made up of leaves, 42% of fruits and the rest is basically made up of flowers.
They feed on more than 100 species of plants from various families, most important of which are Leguminosae, Moraceae, Bignoniaceae, Bombacaceae, Anacardiaceae, Annonaceae and Apocynaceae.
Feeding time varies between tree species, but they tend to spend longer feeding time in trees of the genus Ficus, Brosimum alicastrum and in legumes such as Inga sp and Platypodium elegans.
When they consume leaves, they prefer those that are young because they have a higher amount of protein than mature leaves.
Females tend to have a slightly different diet depending on their reproductive status and age. Pregnant females tend to consume foods with a higher proportion of fat and protein than young females that are not pregnant and those females that already have young and are lactating.
Black howler monkeys can establish groups ranging in size from 2 to 23 individuals. On average they are larger than those made by other species such as A seniculus . Each group can contain between two and three adult males and 7 to 10 adult females.
In general, within the group they have a very peaceful demeanor. Aggressive events only occur when external males or coalitions of satellite males challenge the dominant male for control of the group. If the dominant male is displaced, the new dominant male eliminates all the young to speed up copulation with the females.
The black howler monkeys, like other species of the genus, are characterized by emitting loud “howls” that can be heard between two and three kilometers away. This type of vocalization is used to inform other groups of their presence in a certain area and in this way avoid confrontations over resources or territories.
The females and juveniles accompany the males emitting grunts. In addition there are other vocalizations that include short grunts from the male at any disturbance and short roars with a strong ending after emitting the howls. The females and juveniles also accompany the males emitting loud grunts at any disturbance.
On the other hand, there are a series of barks and moans emitted by females, males and juveniles in various situations.
Howler monkey group ranges can be highly variable. In general, they occupy between 10 and 60 hectares depending on the size of the group and the habitat. In contrast, in sectors with intervened or fragmented tree matrices, high densities of groups can be observed, with territories of between 3 and 7 hectares.
The density in some fragments can exceed 1000 individuals per km 2 . However, the normal thing in forests without intervention is that there are between 16 and 90 individuals per km 2 .
Depending on the availability of resources in the territory of these primates, they can move daily from a few meters to more than a kilometer inside the forest.
During the daytime, these monkeys spend around 60% of their time in rest activities, 15% moving between the arboreal matrices, 15% in feeding activities and around 10% in social activities, which include interactions between group members or grooming, among others.
While moving from one place to another they move in a quadruped way and do not usually jump between trees. When they are feeding they are frequently observed hanging by their prehensile tails or in a resting state sitting or reclining from the branches.
Quadruped locomotion is observed about 50% of the time, climbing or climbing 37% or hanging or suspended the rest of the time. At night, these primates spend the night in medium-sized trees, usually close to one of the feeding sites.
Females of Alouatta palliata prefer to move on the thin branches of the middle canopy and also climb more compared to males.
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