Monkey Forest Tales: What we have learned about Colombian squirrel monkeys over the past 15 years?

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This is the second post of a series in which the findings of this project are presented. In this post, the findings for the Colombian squirrel monkeys are described. Colombian squirrel monkeys are one of the smallest primate species inhabiting the study area.

Most of the time when people see this species in continuous or fragmented areas, they have the impression that there are too many of them. The reality is that because these species live in bigger groups, it looks like there are many but it’s usually just one big group. This has led to the idea that there are common and not in danger of being extinct. However, their numbers are declining, and their habitat has been reduced and fragmented and this affects its survivorship. This is the reason why they are classified as near threatened (Carretero-Pinzon et al 2009, 2013).

Where do you find them and how many of them you will find depending on the amount of forest there are in the landscape. How many fruit trees and how high the forest canopy is, as well as the presence of living fences influence how many of these agile and sometimes noisy small monkeys you can find in fragmented landscapes (Carretero-Pinzon et al. 2017).

The fences made from a line of native trees used by local farmers to divide their pastures (living fences) as well as those trees find standing alone or in small groups in the middle of pastures are important sources of food, especially fruits. Also, living fences are used as part of home ranges (territories), using them to eat fruit, arthropods and to get access to flooded forest fragments in search of small frogs (Carretero-Pinzon & Defler 2018). They use living fences with variable height and also wire fences without any tree cover during their daily movements as well as when dispersing (Carretero-Pinzon et al 2010).

In fragmented landscapes areas where living fences and isolated trees are common usually support bigger groups (> 25 individuals; Carretero-Pinzon et al 2010). These landscape structures help them to survive in highly fragmented landscapes such as agricultural and urban landscapes. They can live in fragments of gallery forest, lowland forest and swamp forest (forest patches composed mainly of Mauritia flexuosa; Carretero-Pinzon & Defler 2018).

As I mentioned in another post, they live in big groups formed by several males, females and their offspring. But in fragmented areas group sizes are smaller than in continuous areas, with groups commonly having between 15 – 43 individuals (Carretero-Pinzon et al 2016). Most groups in continuous areas are of more than 50 individuals. Groups usually have several females (<6 in fragmented areas and > 8 in continuous areas), a couple of males (< 5 in fragmented areas and >6 in continuous areas, Carretero-Pinzon, unpublished data).

Also, in fragmented areas is common that you find subgroups of the same group eating and moving for just a few hours or up to two days apart, especially, in the months in which the fruit offer is reduced in the forest fragments. In continuous are on the contrary subdivision of groups is less common and n some areas is possible to see more than one group of squirrel monkeys eating and moving together (Carretero-Pinzon personal observations). Group territories (home ranges) in fragmented areas don’t overlap very often, while in continuous areas the overlapping can be of almost 50 % of their home ranges (Carretero-Pinzon et al 2016). In both cases there is not evidence of defense of territories and when two groups encounter there is not display of aggression associated with this defense (Carretero-Pinzon personal observations).

In continuous areas (big extensions of a forest), it is common to find solitary males and bachelor groups of only males that are also common in fragmented landscapes. It is also possible to find solitary males using small fragments (< 10 ha) as permanent home ranges for several years and making associations with groups of red howler monkeys. We are not sure if those males are old males just living their last years alone or if they are just dispersing males. However, we know of at least one solitary male who spends at least three years living in a small fragment (4 ha) for three years and then disappears from that fragment (Carretero-Pinzon unpublished data).

Colombian squirrel monkeys in the fragmented areas eat arthropods, fruits, and flowers, in more quantity than in continuous areas but always consuming more arthropods than fruits in both (Carretero-Pinzon et al 2016). The plant species they eat fruits vary in fragmented landscapes where more pioneer plants are used. These are plant species that grow faster and require more light to grow and are easily found in forest fragment edges (Carretero-Pinzon et al 2016).

Mixed troop formations with black-capped capuchins (Sapajus apella) are less frequent in fragmented landscapes compared with continuous areas as I mentioned in a previous post.

References

Carretero-Pinzon X., Defler TR. 2018. Primates and flooded forest in the Colombian Llanos. En: Barnett AA, Matsuda I, Nowak K (eds) Primates in flooded habitats: ecology and conservation, Cambridge University Press, Cambridge, UK.

Carretero-Pinzón, X., T.R. Defler, C.A. McAlpine & J.R. Rhodes. 2017. The influence of landscape relative to site and patch variables on primates distribution in Colombian Llanos. Landscape Ecology 32: 883-896.

Carretero-Pinzón, X., T.R. Defler & M. Ruíz-García. 2016. How does the Colombian squirrel monkey cope with habitat fragmentation? Strategies to survive in small fragments. En: Ruíz-García M, Shostell J.M. (eds). Phylogeny, molecular population genetics, evolutionary biology and Conservation of the Neotropical Primates. Nova Science Publisher Inc., New Yoork, USA. ID book 5975

Carretero-Pinzón, X., T.R. Defler & M. Ruíz-García. 2013. Conservation Status of Saimiri sciureus albigena, an endemic subspecies of squirrel monkeys. In: Especies de Primates Colombianos en Peligro de Extinción. Defler, T.R., Stevenson, P.R., Bueno M.L. & D.C. Guzman.

Carretero-Pinzón, X., T.R. Defler & M. Ruíz-García. 2010. Uso de cercas vivas como corredores biológicos por primates en los Llanos Orientales. In: Primatología en Colombia: avances al principio del milenio. Pereira-Bengoa, V., Stevenson P.R., Bueno M.L. & F. Nassar-Montoya. Fundación Universitaria San Martín. Bogotá, Colombia.

Carretero-Pinzón, X., M. Ruíz-García & T.R. Defler. 2009. The Taxonomy and Conservation Status of Saimiri sciureus albigena: a squirrel monkey endemic to Colombia. Primate Conservation 24: 1 – 6.

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