Monkey Forest Tales: Importance of small fragments in highly fragmented areas

Figura 1 Xyomara Carretero-Pinzón. Decision Point

In this post, the importance of small fragments (less than 5 ha) in highly fragmented areas is highlighted. Traditionally small fragments importance for the survivorship and persistence of primate species has been diminished, except for a study of forest fragments in Africa (Chapman 2006).

In the study area, small fragments of less than 5 hectares are used by primate groups of all species as stepping stones during dispersion events, as part of their daily travels and as dormitories inside of the group’s home range. The use of these fragments seems to be seasonal and influenced by resource availability inside those small fragments and the general resource availability in the whole area.

For example, one of the small fragments, which has been surveyed for several years, has been used by solitary individuals of red howler monkeys, Colombian squirrel monkeys, and dusky titi monkeys as a stepping stone while dispersing in a pasture matrix with living fences. Black-capped capuchins have been observed crossing pastures towards small fragments, where they spend a couple of days before returning to the main forest fragment in which their territory is located.

During this dispersion events, an individual moves and search food in small fragments over several days while moving between fragments in search of a partner to form a new group. In addition to this, small fragments are used by all species as dormitories inside of their home range where their home range includes several fragments connected by living fences.

In addition, small fragments are used by all species in the study area to supplement species home range during the months in which fruit production in the area is reduced. In those months, all primate species travel long distances searching for fruits, using resources available in pastures, living fences and small fragments increasing the distances they travel daily. In the study area, part of these small fragments are located close to natural and artificial lakes that provides individuals of Colombian squirrel monkeys and black-capped capuchins with additional resources such as small frogs and aquatic insect not always available in their main territory.

Additional to primates, these small fragments also serve as stepping stones for birds movement as well as a source of food resources for birds, reptiles and other mammals. The giant anteater, tayras, collared peccaries as well as toucans, woodpeckers, parrots, snakes, and lizards have been observed using these small forest fragments as part of the movements in the landscape. Giant anteaters also used small fragments as dormitories, while tayras used both small fragments and pastures as feeding grounds.

In highly fragmented areas where primate species lives surrounded by human activities, small fragments have been traditionally used as a cover for livestock in large pastures. These fragments increase the heterogeneity of the landscape allowing wildlife persistence and helping wildlife move in the transformed matrix.

Management of biodiversity in highly fragmented areas benefits from the presence and incorporation of small fragments and additional structures such as living fences and isolated trees inside of pastures. Preservation and maintenance of small fragments is an important management action in highly fragmented areas that can be done cost/effectively allowing natural regeneration inside those small fragments.

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Monkey Forest Tales: A good father is important for reproductive success? A dusky titi monkey story

SM Junio 2011 282

Today’s post is focused on the demographic data collected over the years about a dusky titi monkey group. As mentioned in another post about this species, dusky titi monkeys are monogamous and the males are the ones who care for the babies during their first months passing the baby to the female only for feeding.

During the census of all our forest fragments, we collected data on the groups found and their composition. This data helps us to monitor the birth season of dusky titi monkeys, which is early in the year (most babies have been observed during December – January). As well as monitor what happens inside some groups that cannot be followed continuously. One of these groups of dusky titi monkeys has a male who seems to be particularly a good father.

The male of this group is always seen in close proximity of young members of the group and over the years we had been able to monitor at least two infants who have reached their subadult age. These individuals were first detected as infants born in 2004 and 2015, who reach their subadult age after 4 years.

Although we don’t have data of those subadults reproductive success, their success to grow and reach this age is a success for their father as most deaths occur during the first years of individuals of this species. Data from the cause of those infant deaths have not been determined, although we suspect some predation events. Dusky titi monkeys are able to give birth every year, however, not all infants reach the juvenile age and even less reach the subadult age.

This data is important, especially for an endemic species, whose distribution area is reduced and threatened by multiple human activities. In a large survey done in the study area, 22.8 % of the dusky titi monkeys were immatures (infants, juveniles and subadults), a small proportion of the population of these species.

A more detailed study on this demographic data is needed in order to make management actions that preserve this species for the future. But for now, we know that even in fragments of less than < 30 ha, there are groups that are able to contribute to the species population growth. Data from this species movement in the landscape also have shown the resilience of this endemic species to move between forest fragments using pastures, living fences and even crossing secondary roads to disperse.

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Monkey Forest Tales: Why monkey groups do fusion/ fission more often in fragmented areas than in continuous

Unamas - SR Enero 2012 396 (2)

In this post, a story based on some of the observations that we had done over the past years in this project compared with observation done for the same species in a continuous area where I used to work some years before the start of this project.

In continuous area groups of red howler monkeys (Alouatta seniculus), black-capped capuchins (Sapajus apella) and Colombian squirrel monkeys (Saimiri cassiquiarensis albigena) usually move in a cohesive form, i.e. the group dispersion (distance between individuals of the same group) during foraging is short and you can observe most of the group in the same area feeding in the same tree or group of trees.

In fragmented areas were forest size has been reduced due to habitat loss and fragmentation, and where forest had been degraded through selective logging and livestock use of forest, groups of the same species have been observed dispersing more during feeding time, even divided into subgroups and moving separately for up to two days in the case of Colombian squirrel monkeys or just a few hours in the case of red howler monkey.

In Colombian squirrel monkeys, large groups (> more 25 individuals) living in small forest fragments, groups split for up to two days to forage and move independently. Subgroups are composed of females, males, and juveniles, commonly forming subgroups of 10 – 15 individuals. In the study area, this behavior is more common in the months where fruits are less available.

Observations of fusion/ fission patterns had also been observed for red howler monkeys and black-capped capuchins, with groups splitting in solitary individuals or females and juveniles in one subgroup and males and subadults in pairs or alone for up to few hours. In red howler monkeys, these subgroups are formed for just a couple of hours. While in black-capped capuchins we had observed individuals lost from their groups for several hours up to the next day, with intensive calling from the individuals separated from the group.

This pattern of fission/ fusion of groups is a common social structure pattern for other species, like spider monkeys and chimpanzees, but not in the species mentioned above. However, red howler monkeys, black-capped capuchins and Colombian squirrel monkeys live in more cohesive groups where the distance between individuals although variable are not characterized by this type of fission/ fusion structure.

Why this happens? Although not detailed data on the frequency of this behavior, it seems to be more frequent in fragmented areas, especially in forest fragments of less than 50 ha. This pattern can be influenced by resource availability and crowded populations observed in small forest fragments, although more data need to be collected.

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Monkey Forest Tales: A male Colombian squirrel monkey story, Spock

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A picture of Spock resting in a big tree in 2007.

Today’s post is about a male of Colombian squirrel monkey who was first observed in 2005. At that time this male was one of the residents and dominant adult males in a Colombian squirrel monkey group of 42 individuals. He was a male of more than 8 years, probably 10 years in 2005, because of his body features and old scars. He was called Spock because he had a small cut in his right ear, which makes his ear pointed looking like the Start Wars character of that name.

Colombian squirrel monkey groups are composed of several females (5 – 8 females) and a few resident males (3 – 5 males), forming reproductive groups that move and forage together. Additional to this type of group, Colombian squirrel monkey males form groups of only males called bachelor males. Bachelor groups moves and forage independently of a group composed of both sexes and only during the reproductive season (August – September in the study area), bachelor groups are observed following reproductive groups. During these month males become more aggressive and their body accumulates fat on shoulders and thighs that make them look like an American football player.

Males of this species start their reproductive life once they leave their natal groups as solitary males or in small bachelor groups usually formed by a couple of adult males and a few subadult males who move and forage together. Males become resident males usually after several months in which they follow a reproductive group and challenge resident males. In some cases, resident males don’t tolerate them easily and they got back to their solitary life or join other bachelor groups. Although not very common they also can join reproductive groups in the company of an adult female, we only know one case in the study area.

Dominance between males also change and aggression became a tool for males to fight their access to reproductive females. Spock was one of the resident males and a dominant one in one of the reproductive groups in the study area. He was a successful reproductive male in the years 2005 and 2006 where we observed copulating with several females who later those years produce a new baby.

In 2005 – 2007, he remains as one of the dominant males in the group we were following and usually moving close to the females. Colombian squirrel monkey groups move as a group in which females moves in the core of the group with babies and juveniles, while the males move more toward the periphery of the group. Spock used to move close to the core or in the front of the group and always close to the adult females of the group.

Spock was one of the males who fist adapted to our presence following the group and low us to be close to him (3 -5 meter, when at a height of 5 -8 meter, which is close for a wild squirrel monkey). We observed him with the same group until 2009 when one of the students in this project found a dead squirrel monkey who was identified as Spock. He died at an age of around 14 years old. No apparent reason for his death was found, his body didn’t show any marks of predation and when he was found his body was relatively fresh. Although there is not much data on how long Colombian squirrel money males live in the wild, data from males observed in the study area have shown a span of around 24 years form another male from the same group who was last observed in 2017. This male, Van Gogh, was a bit older than Spock when he was first observed and he was one of the least dominant males of the group in 2005, always moving in the back and periphery of the reproductive group.

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