Saimiri cassiquiarensis (Lesson, 1840)

Russell A. Mittermeier, Anthony B. Rylands & Don E. Wilson, 2013, Cebidae, Handbook of the Mammals of the World – Volume 3 Primates, Barcelona: Lynx Edicions, pp. 348-413 : 392-393

2.

Humboldt’s Squirrel Monkey

Saimiri cassiquiarensis

French: Saimiri de Humboldt / German: Humboldt-Totenkopfaffe / Spanish: Mono ardilla de Humboldt

Other common names: Colombian Squirrel Monkey (albigena)

Taxonomy. Simia sciurea cassiquiarensis Lesson, 1840 ,

Rio (Cano) Cassiquiare, Amazonas, Venezuela.

Previously considered a subspecies of S. sciureus . Following a molecular genetic study published in 2009, X. Carretero-Pinzéon concluded that S. cassiquiarensis albigena should be considered a distinct species. Two subspecies recognized here.

Subspecies and Distribution.

S. c. cassiquiarensisLesson, 1840 — ColombianAmazon (betweenriosVichadaandApaporisWtotheupperriosGuaviareandApaporisintheAndes), SVenezuela (upperOrinoco-Cassiquiare), andtheBrazilianAmazonNoftheRioSolimoes (WoftheRioNegroandRioDeminiandNoftheRioJapura).

S. c. albigenavon Pusch, 1942 — C Colombia, in a small area between the E slopes of the Cordillera Oriental and the Eastern Llanos, from Boyaca and Arauca departments S to the upper Rio Guaviare in Meta, and the upper Rio Magdalena in Huila departments to elevations of 1500 m; the E limits of the distribution in the departments of Arauca and Casanare are unknown.

Descriptive notes. Head-body 25-37 cm (males) and 28-34 cm (females), tail 38-45 cm (males) and 36-43 cm (females); weight 650-1125 g (males) and 550-1200 g (females). The nominate subspecies of Humboldt’s Squirrel Monkeyis very similar in its coloration and size to the Guianan Squirrel Monkey (S. sciureus ) but has a more intense tawny (golden-yellow) basal section to hairs on the crown (the Guianan Squirrel Monkey is more gray-crowned). Nominate female Humboldt’s Squirrel Monkeys have two black lines above their ears (temporal band) that extend back to the nape and forward in front of the ears (preauricular patch or sideburns). Males lack temporal bands and do not have a tuft of black hairs in front oftheir ears. There is a brighter reddishtan coloring on the back, and a weakly contrasting, light nuchal collar. Forearms are more orangey in the nominate subspecies of Humboldt’s Squirrel Monkey (gray in the Guianan Squirrel Monkey). The “Colombian Squirrel Monkey” (S. ¢. albigena) is also similar to the nominate subspecies of the Guianan Squirrel Monkey, but with mainly grayish-agouti (grizzled gray) forearms and hands, and its back is more orange-toned. The crown and nape are grayish or buffy-agouti. The white facemask of the male Colombian Squirrel Monkey extends to the ears (no sideburns), but sometimes there is a pale agouti patch in front of the ears, which are tufted. Female Colombian Squirrel Monkeys have thin dark sideburns.

Habitat. The nominate subspecies of Humboldt’s Squirrel Monkey occurs in the tall humid forests of the Guiana Shield in the basins of the Rio Negro, north of the Rio Japura in Brazil to the north in the Federal Territory of Amazonas in Venezuela and west into Colombia, north of the Apaporis (including part of Colombia’s Orinoco Region, just north of the lower and middle Rio Guayabero) to the Chiribiquete Plateau. In these areas, forest canopies reach 25-30 m and are on poorsoils (oligotrophic, hydromorphic laterite, and podzols, and quartz sands). Tall terra firma forests are intermixed with islands of white sand scrub and savanna (“campina”) and small-leaved and sclerophytic white sand forest (“campinarana” or caatinga forest), along with swamp forests (“chavascal”), Mauritia palm swamps, and seasonally inundated black-water forests (igapo). The Chiribiquete Plateau is characterized by sclerophytic dwarf scrub. The Colombian Squirrel Monkey occurs in the eastern Andean region of Colombia in low-canopy gallery forests of the Eastern Llanos, sclerophyllous hillside forest of the foothills of the Cordillera Oriental of the Andes, and Mauritia palm swamp forest.

Food and Feeding. Colombian Squirrel Monkeys eat principally fruits and insects. They have been reported catching large caterpillars, orthopterans, and cicadas. Near San Martin in the Llanos where they have been studied, there are distinct seasons: a dry season in December—March and a wet season in April-November. Fruits are abundant only in the late dry season and early wet season (January-June), and insects are scarcer in the mid-dry season (February-March).

Breeding. In the group of Humboldt’s Squirrel Monkeys studied by R. Thorington, Jr. four infants were born during 31 days in February—early March, and a fifth female gave birth in the beginning of April at the end of the dry season and early wet season. When pregnant and nursing, females were less active and spent more time in association with a group of Large-headed Capuchins ( Sapajus macrocephalus ). They foraged more slowly and rested more than other group members. Thorington did not observe allocare by other females, butjuveniles were notably interested in infants and traveled with pregnant females. At Sierra de la Macarena National Natural Park, Colombia, births occurred in April-June.

Activity patterns. Colombian Squirrel Monkeys are most active in the early to midmorning and the middle to late afternoon. At midday, they rest for 1-2 hours. In the cool early morning, they stop and rest in a huddled position, but toward the hotter middle of the day, they stretch out and sprawl.

Movements, Home range and Social organization. Group sizes of Colombian Squirrel Monkeys in Sierra de la Macarena National Natural Park were 25-35 individuals. Thorington carried out a short study of the Colombian Squirrel Monkey in 1965 in a gallery forest in the Eastern Llanos, east of San Martin in the Meta Department. He observed a group of 18-22 individuals that included three adult males,five adult females, and ten 1-3year-oldjuveniles. During the day, the group split into subgroups, sometimes adult males separated from females andjuveniles. Subgroups reunited at midday and also at the end of the day to sleep together. Male Colombian Squirrel Monkeys disperse from their natal groups and form all-male groups. Lone males have been observed following spider monkeys ( Ateles ) in Sierra de la Macarena. At San Martin, Colombian Squirrel Monkeys occasionally associate with Large-headed Capuchins, and more often in August—January when insect abundance is higher than at other times. There was no effect of fruit abundance on these associations, but they were most frequent when both fruit and prey were most abundant. It is believed that associations between the two species are relatively infrequent compared with other species of squirrel monkeys because of the overall scarcity of, and competition for, fruit. For the nominate subspecies, average group sizes were ten (n = 3) at the clear-water creek, Cano Pintadillo, and 18 (n = 10) at Caparu on the northern margin of Lago Taraira—both sites just north of the lower black-water Rio Apaporis in Colombia. Densities of squirrel monkeys at these two sites, reported by E. Palacios and C. Peres in 2005, were very low,a finding attributed to the very heavy rainfall and nutrient poor soils of the area: 0-5 groups/km?or 5-4 ind/km? at Cano Pintadillo and 0-2 groups/km? or 3-1 ind/km* at Caparu. Long-term primate studies have been conducted at Caparu, and censuses in 1984-1986 also confirmed low densities of squirrel monkeys at 8-8 ind/km? in terra firma and 7-1 ind/km? in igapo, with groupsizes of ¢.15 individuals. Somewhat higher densities of 12-7 ind/km? were recorded for Colombian Squirrel Monkeys in Tinigua National Natural Park, Colombia. T. Defler recorded Humboldt’s Squirrel Monkeys infrequently, and they were usually associated with Large-headed Capuchins and Humboldt’s Woolly Monkeys ( Lagothrix lagothricha), with both in the terra firma forest but just with the woolly monkeys in the igapo.

Status and Conservation. CITES Appendix II. The nominate subspecies is classified as Least Concern (as S. sciureus cassiquiarensis ) and the Colombian Squirrel Monkey as Near Threatened (as S. s. albigena) on The IUCN Red List. The geographic distribution of the Colombian Squirrel Monkey is ¢.100,000 km? but it has been reduced to ¢.60,000 km* by the spread of oil palm plantations. Fragmentation of the gallery forests and forest patches where they occur in the Llanos has caused local extinctions, particularly over large areas in the vicinity of large towns, such as Gigante and Garzon in the northern part of their distribution. Besides oil palm plantations, major causes of forest loss and fragmentation are cattle ranching, subsistence farming, petroleum extraction and exploration, and illegal crops such as coca. Squirrel monkeys have large home ranges, and they are lost from even quite large forest fragments when they are completely isolated. Fence rows (live and wire fences, hedgerows, and trees) play a very important role as corridors between forest fragments, particularly at times of food scarcity. Populations of Colombian Squirrel Monkeys in the upper Magdalena Valley of the Huila Department are particularly threatened by habitat loss. In the 1960s and early 1970s, the Colombian Squirrel Monkey suffered from capture for sale as pets and export for biomedical research. In Colombia, a small population has been found in Cueva de los Guacharos National Natural Park, and they also occur in Tinigua and Sierra de la Macarena national natural parks in their south-western distribution. It is believed that their numbers and geographic distribution are diminishing to the extent that they should be reclassified as Vulnerable or even Endangered. The nominate subspecies occurs in Pico da Neblina and Jau national parks, Juami-Japura Ecological Reserve, and Amana State Sustainable Development Reserve in Brazil; Yaigojé Apaporis and Serrania de Chiribiquete national natural parks and Nukak and Puinawai national natural reserves in Colombia; and Parima Tapirapeco, Yapacana, Duida-Marahuaca, and Serrania de la Neblina national parks in Venezuela.

Bibliography. Baldwin & Baldwin (1971), Carretero-Pinzén, Defler & Ruiz-Garcia (2008, 2010), Carretero-Pinzén, Ruiz-Garcia & Defler (2009), Defler (2003b, 2004), Hernandez-Camacho & Cooper (1976), Hershkovitz (1949, 1984), Klein & Klein (1976), Lavergne et al. (2009), Palacios & Peres (2005), Thorington (1968b, 1985).

Figures

1. Central American Squirrel Monkey (Saimiri oerstedia), 2. Humboldt’s Squirrel Monkey (Saimiri cassiquiarensis), 3. Ecuadorian Squirrel Monkey (Saimiri macrodon), 4. Golden-backed Squirrel Monkey (Saimiri ustus), 5. Guianan Squirrel Monkey (Saimiri sciureus), 6. Black-capped Squirrel Monkey (Saimiri boliviensis)

Subspecies and Distribution. S. c. cassiquiarensisLesson, 1840 — ColombianAmazon (betweenriosVichadaandApaporisWtotheupperriosGuaviareandApaporisintheAndes), SVenezuela (upperOrinoco-Cassiquiare), andtheBrazilianAmazonNoftheRioSolimoes (WoftheRioNegroandRioDeminiandNoftheRioJapura). S. c. albigenavon Pusch, 1942 — C Colombia, in a small area between the E slopes of the Cordillera Oriental and the Eastern Llanos, from Boyaca and Arauca departments S to the upper Rio Guaviare in Meta, and the upper Rio Magdalena in Huila departments to elevations of 1500 m; the E limits of the distribution in the departments of Arauca and Casanare are unknown.