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Status of the Eastern Patas Monkey on Lolldaiga Hills Ranch, Laikipia, Kenya

By Yvonne de Jong, Tom Butynski & Julius Mathiu

Among East Africa’s primates, the Eastern Patas Monkey Erythrocebus patas pyrrhonotus is of special concern. Historically, in Kenya, this subspecies occurred in the west, northwest, centre and south, with a geographic range of ca. 93,000 km². The range has, however, declined to ca. 52,500 km² (56% of the historic range), and the gaps among populations have increased (De Jong et al. 2008; De Jong & Butynski 2014).

Eastern Patas Monkey Erythrocebus patas pyrrhonotus, Kidepo Valley National Park, Uganda.

During the April 2016 IUCN/SSC African Primate Red List Assessment Workshop in Rome, we raised the degree of threat status of Patas Monkey Erythrocebus patas from ‘Least Concern’ to ‘Near Threatened’ (De Jong & Butynski 2017a). Erythrocebus patas pyrrhonotus, the subspecies present on Lolldaiga Hills Ranch, was assessed as ‘Vulnerable’ (De Jong & Butynski 2017b). The justification for this is as follows:

“Although E. p. pyrrhonotus has a wide geographic range, there is an observed population reduction throughout the range. This decline is expected to continue as the causes (mainly habitat degradation, fragmentation, and loss) are on-going. Extent of occurrence and area of occupancy are in decline. The current level of exploitation is not likely to be reduced.” (De Jong & Butynski 2017b).

Today, the Eastern Patas Monkey (hereafter referred to as ‘Patas’) is one of Kenya’s most threatened primates (De Jong et al. 2008; De Jong & Butynski 2012, 2017).

Current geographic range of the Eastern Patas Monkey Erythrocebus patas pyrrhonotus in Kenya.

Patas are supported by Laikipia’s vast Whistling Thorn Acacia drepanolobium woodlands, where it naturally occurs at low densities (0.2–1.5 individuals/km²; Chism & Rowell 1988; Isbell & Chism 2007). In Laikipia, groups are typically between 13 and 56 individuals. Home ranges are extensive, ranging between 23–40 km² (Chism & Rowell 1988; Enstam & Isbell 2004). Patas have always been at low density on Lolldaiga Hills Ranch, occurring mainly in the North Valley (Mizutani 1995; Robert Wells pers. comm.; Lance Thomlinson pers. comm.; Ken Wreford-Smith pers. comm.).  

As part of our current Patas survey in eastern Laikipia County, we visited ranger posts on Lolldaiga Hills Ranch during April 2017. With the help of photographs of Patas and a map, we interviewed 33 rangers, herders, and others. We asked if they had seen Patas on the Ranch and, if so, when, where, and how many? In addition, we asked if they thought Patas had decline in abundance and, if so, what they believe to be the main reason. We also examined Lolldaiga’s Security Logbook for records of Patas.  

Eastern patas monkey Erythrocebus patas pyrrhonotus, Kidepo Valley National Park, Uganda.

We obtained records of Patas from northeast, central north, southwest, and southeast Lolldaiga (Figure 1). According to the interviewees, Patas were last seen in 2015 in the northeast (Northern Borehole and Mlima Kofia area). Up to at least July 2014, south Lolldaiga was occasionally visited by 1–2 solitary adult males. Twelve of the 33 interviewees had never seen Patas on Lolldaiga. Most interviewees had been employed on Lolldaiga for <2 years.

When Lolldaiga’s Patas population was first surveyed (1979-1981), there were about 36 individuals in two groups (Isbell & Chism 2007; Table 1.). At present, at most, there are 1–2 transient solitary adult males and a group of 3–4 individuals that occasionally come onto the Ranch.

Table 1. Changes in the population of Patas Monkey on Lolldaiga Hills Ranch, Laikipia, central Kenya

Survey period 1979–1981
Isbell & Chism (2007)
Isbell & Chism (2007)
De Jong, Butynski & Mathiu (2017)
De Jong, Butynski & Mathiu (2017)
Number of groups and individuals 2 groups
(17 & 19 individuals)
1–2 groups (total 50 individuals) Group of <8 individuals using Lolldaiga Hills Ranch, Makurian Group Ranch, and Ole Naishu Ranch. Group of 3 individuals using Lolldaiga Hills Ranch and, most likely, Ole Naishu Ranch. 1–2 solitary adult males. No records. Probably, occasionally, a group of 3–4 individuals and 1–2 solitary adult males.


Patas have not been reported for Lolldaiga since 2015, and tens of thousands of camera trapping hours have been accumulated since August 2014 without a single photograph of Patas. Considering their shy behaviour and large home ranges, this does not, however, mean that Lolldaiga no longer supports Patas. It seems likely that one small group of Patas and 12 solitary adult male Patas still make occasional use of Lolldaiga, but spend most of their time on south Makurian Group Ranch and/or northwest Ole Naishu Ranch.

Figure 1. Results of the April 2017 survey of the Eastern Patas Monkey Erythrocebus patas pyrrhonotus on Lolldaiga Hills Ranch, Laikipia County, central Kenya.

So what is causing the decline of Patas on Lolldaiga? The most common opinion among interviewees is that there has been a considerable loss of Whistling Thorn woodland as a result of destruction by elephants…which have continued to increase on the landscape. Whistling Thorn is a key tree species for Patas in Laikipia (see LHRP Newsletter 6). Interviewees also said that the livestock and herders on north Lolldaiga disturb Patas.

At the Western Borehole, rangers thought that leopard numbers had increased and that this species was affecting the Patas population. According to interviewees, availability of water on Lolldaiga has remained unchanged and is not the cause of the decline in Patas numbers.

Eastern Patas Monkey Erythrocebus patas pyrrhonotus along the Ole Naishu Ranch – Borana Ranch border. Photograph by Yvonne de Jong and Tom Butynski.

Similar Patas surveys of staff on neighbouring properties, particularly Ole Naishu Ranch and Makurian Group Ranch, are expected to provide additional information on Patas in this region, particularly the size and location of the home range of the ‘Mlima Kofia’ Patas Group.

We thank Paul Benson, Per Aronsson, and all Lolldaiga staff who helped during this survey.


References: Chism, J & Rowell, TE 1988. The natural history of patas monkeys. In: A Primate Radiation: Evolutionary Biology of the African Guenons, A. Gautier-Hion, F. Bourlière, J. P. Gautier and J. Kingdon (eds.), pp.412–438. Cambridge University Press, Cambridge, UK; De Jong, YA & Butynski, TM 2012. The primates of East Africa: country lists and conservation priorities. African Primates 7: 135–155; De Jong, YA & Butynski, TM 2014. Notes on the Primates of Northwestern Kenya. Unpublished report; De Jong, YA & Butynski, TM 2017a. Erythrocebus patas. The IUCN Red List of Threatened Species 2017. IUCN/SSC Gland, Switzerland; De Jong, YA & Butynski, TM 2017b. Erythrocebus patas pyrrhonotus. The IUCN Red List of Threatened Species 2017. IUCN/SSC Gland, Switzerland; De Jong, YA, Butynski, TM & Nekaris, KA 2008. Distribution and conservation of the patas monkey Erythrocebus patas in Kenya. Journal of East African Natural History 97: 83–102; Enstam, KL & Isbell, LA 2004. Microhabitat preferences and vertical use of space by patas monkeys (Erythrocebus patas) in relation to predation risk and habitat structure. Folia Primatologica 75: 70–84; Isbell, LA & Chism, J 2007. Distribution and abundance of patas monkeys (Erythrocebus patas) in Laikipia, Kenya, 1979-2004. American Journal of Primatology 69: 1223–1235; Mizutani, F 1995. The ecology of leopards and their impact on livestock ranches in Kenya. PhD dissertation. University of Cambridge, Cambridge.

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