Staff profile

My main research interests are in the behavioural ecology of primates and other large mammals and in particular in understanding how animals respond to the risk of predation. I run the Primate & Predator Project based at the Endangered Wildlife Trust's Medike Nature Reserve in the Soutpansberg Mountains, South Africa, with a sister site at the Alldays Wildlife and Communities Research Centre. I have previously managed other projects in South Africa based at De Hoop Nature Reserve and in the Kruger National Park. My postgraduate students have conducted projects across southern Africa, and increasingly our work is examining mammalian conservation and human-wildlife interactions from an interdiscplinary perspective. I also have interests in applying evolutionary principles to explore a number of different aspects of human behaviour, particularly in understanding the role of the colour red in human competitive interactions.

I am interested in supervising students in any of my research interests, including primate behaviour and ecology, predator-prey interactions and interdisciplinary approaches to conservation and human-wildlife conflict.

Primate & Predator Project

Protected areas are the cornerstone of local, regional, and global strategies for biodiversity conservation. As human populations continue to rise and human activities convert and degrade lowland habitats, mountainous regions are increasingly important to species conservation. Mountainous areas are often noted for high concentrations of endemic species of animals and plants, and thus represent an important focus for conservation research. Our study aims to understand the ecology of species living in a biodiversity hotspot in the mountains of South Africa and examines the threat of human activity to species conservation.

Our project is based in the Medike Nature Reserve within the Soutpansberg Mountain Range, an area recognized nationally as a centre of endemism and biodiversity. The mountains fall within the Vhembe UNESCO Biosphere Reserve and form part of the North-Eastern Escarpment Bio-region, an area highlighted by the South African National Biodiversity Institute as a priority for conservation research. Our study is addressing this need and we work in close collaboration with the Endangered Wildlife Trust.

• Primate Behaviour and Ecology
• Predator-Prey Interactions
• Felid Behaviour and Ecology
• Conservation and Human-Wildlife Conflict

• Evolutionary Anthropology

• Endangered Wildlife Trust
• PPP Blog
• PPP Facebook
• PPP Twiter:
• Primate & Predator Project

Available for media contact about:

• Primate behaviour: Ecology
• Biological and Biomedical Sciences: Conservation
• Anthropology: Evolutionary psychology

Chapter in book

• Hill, R.A. (2020). Reflections on 'Babooning'. In Curious about Nature: A Passion for Fieldwork. Burt, T. & Thompson, D. Cambridge Cambridge University Press. 218-222.
• Hill, R.A. (2019). From 150 to 3 Dunbar’s numbers. In Dunbar's Number. Shankland, D. Sean Kingston Publishing. 45.
• Hill, R.A. (2017). Dunbar, R.I.M. (Robin Ian MacDonald). In The International Encyclopaedia of Primatology. Fuentes, A. Chichester, UK Hoboken, NJ: John Wiley & Sons.
• Nowak, K., Hill, R.A., Wimberger, K. & le Roux, A. (2016). Risk-taking in samango monkeys in relation to human observers at two sites in South Africa. In Ethnoprimatology: Primate Conservation in the 21st Century. Waller, M. Springer. 301-314.
• Maier, M.A., Hill, R.A., Elliot, A.J. & Barton, R.A. (2015). Color in achievement contexts in humans. In Handbook of color psychology. Elliot, A.J., Fairchild, M.D. & Franklin, A. Cambridge: Cambridge University Press. 568-584.
• Hill, R.A., Sellers, W.I., Logan, B. & Zapala, J. (2012). An agent-based model of group decision-making in baboons. In Modelling Natural Action Selection. Seth, A., Prescott, T. & Bryson, J. Cambridge University Press. 454-476.
• Wiedemann, D., Barton, R.A. & Hill, R.A. (2012). Evolutionary approaches to sport. In Applied Evolutionary Psychology. Roberts, S.C. Oxford University Press. 290-307.
• Hill, R.A. (2008). Nonhuman primate approaches to landscapes. In Handbook of Landscape Archaeology. David, B. & Thomas, J. Walnut Creek, California: Left Coast Press, Inc. 95-101.
• Hill, R.A. & Weingrill, T. (2007). Predation risk and habitat use in chacma baboons (Papio hamadryas ursinus). In Primates Anti-Predator Strategies. Gursky, S. & Nekaris K.A.I. New York: Kluwer Academic Publishers. 339-354.
• Sellers, W.I., Hill, R.A. & Logan, B. (2005). Biorealistic simulation of baboon foraging using agent-based modelling. In Modelling natural action selection: Proceedings of an international workshop. Bryson, J.J., Prescott, T.J. & Seth, A.K. AISB Press. 127-134.
• Hill, R.A. (2005). Day length seasonality and the thermal environment. In Primate seasonality: implications for human evolution. Brockman, D.K. & van Schaik, C.P. Cambridge: Cambridge University Press. 197-213.
• Hill, R.A. & Cowlishaw, G. (2002). Foraging female baboons exhibit similar patterns of antipredator vigilance across two populations. In Eat or be eaten: predator sensitive foraging among primates. Miller, L.E. Cambridge: Cambridge University Press. 187-204.

Journal Article

• McKaughan, J.E.T., Stephens, P.A. & Hill, R.A. (2023). Estimating mesocarnivore abundance on commercial farmland using distance sampling with camera traps. Ecological Solutions and Evidence 4(2): e12229.
• Stewart, Peter S., Stephens, Philip A., Hill, Russell A., Whittingham, Mark J. & Dawson, Wayne (2023). Model Selection in Occupancy Models: Inference versus Prediction. Ecology 104(3): e3942.
• Green, Sian E., Stephens, Philip A., Whittingham, Mark J. & Hill, Russell A. (2023). Camera trapping with photos and videos: implications for ecology and citizen science. Remote Sensing in Ecology and Conservation 9(2): 268-283.
• Allan, Andrew T.L., LaBarge, Laura R., Howlett, Caroline, Bailey, Annie L., Jones, Benjamin, Mason, Zachary, Pinfield, Thomas, Schröder, Felix, Whitaker, Alex, White, Amy F., Wilkinson, Henry & Hill, Russell A. (2023). Patterns of predation and meat-eating by chacma baboons in an Afromontane environment. Folia Primatologica 94(1): 13–36.
• Hsing, Pen-Yuan, Hill, Russell, Smith, Graham, Bradley, Steven, Green, Sian, Kent, Vivien, Mason, Samantha, Rees, Jonathan, Whittingham, Mark, Cokill, Jim, MammalWeb citizen scientists & Stephens, Philip (2022). Large-scale mammal monitoring: the potential of a citizen science camera-trapping project in the United Kingdom. Ecological Solutions and Evidence 3(4): e12180.
• LaBarge, Laura R., Allan, Andrew T.L., Berman, Carol M., Hill, Russell A. & Margulis, Susan W. (2022). Cortisol metabolites vary with environmental conditions, predation risk, and human shields in a wild primate, Cercopithecus albogularis. Hormones and Behavior 145: 105237.
• Allan, A.T.L., White, A. & Hill, R.A. (2022). Intolerant baboons avoid observer proximity, creating biased inter-individual association patterns. Scientific Reports 12: 8077.
• Mason, S.S., Hill, R.A., Whittingham, M.J., Cokill, J., Smith, G.C. & Stephens, P.A. (2022). Camera trap distance sampling for terrestrial mammal population monitoring: lessons learnt from a UK case study. Remote Sensing in Ecology and Conservation 8(5): 717-730.
• Findlay, L.J., Lucas, C., Walker, E.M., Evers, S. & Hill, R.A. (2022). Testing the Short-Term Effectiveness of Various Deterrents for Reducing Crop Foraging by Primates. African Journal of Wildlife Research 52(1): 29-43.
• Walton, B.J., Findlay. L.J. & Hill, R.A. (2022). Camera traps and guard observations as an alternative to researcher observation for studying anthropogenic foraging. Ecology and Evolution 12(4): e8808.
• Parker, Edwin J., Hill, Russell A. & Koyama, Nicola F. (2022). Behavioral responses to spatial variation in perceived predation risk and resource availability in an arboreal primate. Ecosphere 13(2): e3945.
• Faure, J. Philip B., Swanepoel, Lourens H., Cilliers, Deon, Venter, Jan A. & Hill, Russell A. (2022). Estimates of carnivore densities in a human-dominated agricultural matrix in South Africa. Oryx 56(5): 774-781.
• Allan, A.T.L., Bailey, A.L. & Hill, R.A. (2021). Consistency in the flight and visual orientation distances of habituated chacma baboons after an observed leopard predation. Do flight initiation distance methods always measure perceived predation risk? Ecology and Evolution 11(21): 15404-15416.
• Allan, A.T.L. & Hill, R.A. (2021). Definition and interpretation effects: How different vigilance definitions can produce varied results. Animal Behaviour 180: 197-208.
• Coleman, B.T., Setchell, J.M. & Hill, R.A. (2021). Seasonal variation in the behavioural ecology of samango monkeys (Cercopithecus albogularis schwarzi) in a southern latitude montane environment. Primates 62(6): 1005-1018.
• Parker, E.J., Koyama, N.F. & Hill, R.A. (2021). Habitat selection of an endangered primate, the samango monkey (Cercopithecus albogularis schwarzi): integrating scales to prioritise habitat for wildlife management. Ecology and Evolution 11(12): 8014-8026.
• Stewart, PS, Hill, RA, Stephens, PA, Whittingham, MJ & Dawson, W (2021). Impacts of invasive plants on animal behaviour. Ecology Letters 24: 891-907.
• Williams, K.S., Williams, S.T., Welch, R.J., Marneweck, C.J., Mann, G.T., Pitman, R.T., Whittington-Jones, G., Balme, G.A., Parker, D.M. & Hill, R.A. (2021). Assumptions about fence permeability influence density estimates for brown hyaenas across South Africa. Scientific Reports 11: 620.
• LaBarge, L.R., Allan, A.T.L., Berman C.M., Hill, R.A. & Margulis, S.W. (2021). Extent of threat detection depends on predator type and behavioral context in wild samango monkey groups. Behavioral Ecology and Sociobiology 75: 13.
• Walton, Ben J., Findlay, Leah J. & Hill, Russell A. (2021). Insights into short‐ and long‐term crop‐foraging strategies in a chacma baboon (Papio ursinus) from GPS and accelerometer data. Ecology and Evolution 11(2): 990-1001.
• Williams, K.S., Pitman, R.T., Mann, G.T., Whittington-Jones, G., Comley, J., Williams, S.T., Hill, R.A., Balme, G.A. & Parker, D.M (2021). Utilising bycatch camera trap data for broad-scale occupancy and conservation: a case study on brown hyaena (Parahyaena brunnea). Oryx 55(2): 216-226.
• Allan, A.T.L., Bailey, A.L. & Hill, R.A. (2020). Habituation is not neutral or equal: Individual differences in tolerance suggest an overlooked personality trait. Science Advances 6(28): eaaz0870.
• Parker, E., Hill, R.A., Allan, A.T.L., Howlett, C. & Koyama, N.F. (2020). Influence of food availability, plant productivity and indigenous forest use on ranging behavior of the endangered samango monkey (Cercopithecus albogularis schwarzi), in the Soutpansberg Mountains, South Africa. Integrative Zoology 15(5): 385-400.
• Stringer, S.D., Hill, R.A., Swanepoel,L., Dalrymple, S.E., Linden, B. & Koyama, N.F. (2020). Assessing the role of a mammalian frugivorous species on seed germination potential depends on study design: A case study using wild samango monkeys. Acta Oecologica 106: 103584.
• Hsing, P.-Y., Coghill, L., Ryder, J., Austin, M., Dooley, S., Ellison, A., Fenwick, C., Garland, M., Humphrey, P., Proudlock, H., Robson, A., Steer, C., Turnbull, L., Kent, V.T., Bradley, S., Hill, R.A., Ascroft, R. & Stephens, P.A. (2020). Citizen scientists: school students conducting, contributing to and communicating ecological research – experiences of a school–university partnership. School Science Review 101(376): 67-74.
• LaBarge, L.R., Allan, A.T.L., Berman, C.M., Margulis, S.W. & Hill, R.A. (2020). Reactive and pre-emptive spatial cohesion in a social primate. Animal Behaviour 163: 115-126.
• Stringer, S.D., Hill, R.A., Swanepoel, L. & Koyama, N.F. (2020). Adapting methodology used on captive subjects for estimating gut passage time in wild monkeys. Folia Primatologica 91(4): 417-432.
• Green, S.E., Rees, J.P., Stephens, P.A., Hill, R.A. & Giordano, A.J. (2020). Innovations in Camera Trapping Technology and Approaches: The Integration of Citizen Science and Artificial Intelligence. Animals 10(1): 132.
• Findlay, L.J. & Hill, R.A. (2020). Baboon and vervet monkey crop-foraging behaviors on a commercial South African farm: Preliminary implications for damage mitigation. Human–Wildlife Interactions 14(3): 505-518.
• LaBarge, L.R., Hill, R.A., Berman, C.M., Margulis, S.W. & Allan, A.T.L. (2020). Anthropogenic influences on primate antipredator behavior and implications for research and conservation. American Journal of Primatology 82(2): e23087.
• Ayers, A.M., Allan, A.T.L., Howlett, C., Tordiffe, A.S.W., Williams, K.S., Williams, S.T. & Hill, R.A. (2020). Illuminating Movement? Nocturnal Activity Patterns in Chacma Baboons. Journal of Zoology 310(4): 287-297.
• Findlay, L.J. & Hill, R.A. (2020). Field guarding as a crop protection method: Preliminary implications for improving field guarding. Human-Wildlife Interactions 14(3): 20, 519-530.
• Faure J.P.B., Holmes N.J., Watson L.H. & Hill R.A. (2019). Brown Hyaena (Parahyaena brunnea) diet composition from Zingela Game Reserve, Limpopo Province, South Africa. African Zoology 54(2): 119-124.
• de Raad, A.L. & Hill, R.A. (2019). Topological spatial representation in wild chacma baboons (Papio ursinus). Animal Cognition 22(3): 397-412.
• Baauw, Anna H., Heyne, Heloise, Williams, Kathryn S., Hill, Russell A., Heitkönig, Ignas M.A. & Williams, Samual T. (2019). First records of Hyalomma rufipes and Ixodes neitzi (Acari: Ixodidae) found on large carnivores in South Africa. Ticks and Tick-borne Diseases 10(1): 128-131.
• Williams, K.S., Williams, S.T., Fitzgerald, L.E., Sheppard, E.C. & Hill, R.A. (2018). Brown hyaena and leopard diets on private land in the Soutpansberg Mountains, South Africa. African Journal of Ecology 56(4): 1021-1027.
• Hsing, P.-Y., Bradley, S.P., Kent, V.T., Hill, R.A., Smith, G.C., Whittingham, M.J., Cokill, J., Crawley, D., MammalWeb Volunteers, & Stephens, P.A. (2018). Economical crowdsourcing for camera trap image classification. Remote Sensing in Ecology and Conservation 4(4): 361-374.
• Allan, A.T.L. & Hill, R.A. (2018). What have we been looking at? A call for consistency in studies of primate vigilance. American Journal of Physical Anthropology 165(S65): 4-22.
• Atickem, A., Simeneh, G., Bekele, A., Mekonnen, T., Sillero-Zubiri, C., Hill, R.A. & Stenseth, N.C. (2017). African wolf diet, predation on livestock and conflict in the Guassa Mountains of Ethiopia. African Journal of Ecology 55(4): 632-639.
• Williams, S.T., William, K.S., Lewis, B.P. & Hill, R.A. (2017). Population dynamics and threats to an apex predator outside protected areas: Implications for carnivore management. Royal Society Open Science 4(4): 161090.
• Chase Grey, J.N., Bell, S. & Hill, R.A. (2017). Leopard diets and landowner perceptions of human wildlife conflict in the Soutpansberg Mountains, South Africa. Journal for Nature Conservation 37: 56-65.
• Wimberger, K., Nowak, K. & Hill, R.A. (2017). Reliance on exotic plants by two groups of threatened samango monkeys, Cercopithecus albogularis labiatus, at their southern range limit. International Journal of Primatology 38(2): 151-171.
• Pitman, R.T., Fattebert, J., Williams, S.T., Williams, K.S., Hill, R.A., Hunter, L.T.B., Robinson, H., Power, J., Swanepoel, L.H., Slotow, R. & Balme, G. (2017). Cats, connectivity and conservation: incorporating datasets and integrating scales for wildlife management. Journal of Applied Ecology 54(6): 1687-1698.
• Pitman, R.T., Fattebert, J., Williams, S.T., Williams, K.S., Hill, R.A., Hunter, L.T.B., Slotow, R. & Balme, G.A. (2017). The conservation costs of game ranching. Conservation Letters 10(4): 402-412.
• Nowak, K., Wimberger, K., Richards, S.A., Hill, R.A. & le Roux, A. (2017). Samango monkeys (Cercopithecus albogularis labiatus) manage risk in a highly seasonal, human-modified landscape in Amathole Mountains, South Africa. International Journal of Primatology 38(2): 194-206.
• Howlett, C. & Hill, R.A. (2017). Can zoo enclosures inform exclosure design for crop-raiding primates? A preliminary assessment. African Journal of Ecology 55(4): 727-730.
• Nowak, K., Richards, S., le Roux, A. & Hill, R. A. (2016). The influence of live-capture on the risk perceptions of habituated samango monkeys. Journal of Mammalogy 97(5): 1461-1468.
• Williams, S.T., Williams, K.S., Joubert, C.J. & Hill, R.A. (2016). The impact of land reform on the status of large carnivores in Zimbabwe. PeerJ 4: e1537.
• Constant, N.L., Bell, S. & Hill, R.A. (2015). The impacts, characterisation and management of human-leopard conflict in a multi-use land system in South Africa. Biodiversity and Conservation 24(12): 2967-2989.
• Wiedemann, D., Burt, D.M., Hill, R.A. & Barton, R.A. (2015). Red clothing increases perceived dominance, aggression and anger. Biology Letters 11(5): 20150166.
• Howlett, C., Setchell, J.M., Hill, R.A. & Barton, R.A. (2015). The 2D:4D digit ratio and social behaviour in wild female chacma baboons (Papio ursinus) in relation to dominance, aggression, interest in infants, affiliation and heritability. Behavioral Ecology and Sociobiology 69(1): 61-74.
• Nowak, K., le Roux, A., Richards, S.A., Scheijen, C. & Hill, R.A. (2014). Human observers impact habituated samango monkeys’ perceived landscape of fear. Behavioral Ecology 25(5): 1199-1204.
• Lawson, J.F., James, C., Jannson, A.-U.C., Koyama, N.F. & Hill, R.A. (2014). A comparison of heterosexual and homosexual mating preferences in personal advertisements. Evolution and Human Behavior 35(5): 408-414.
• Coleman, B.T. & Hill, R.A. (2014). Biogeographic Variation in the Diet and Behaviour of Cercopithecus mitis. Folia Primatologica 85(5): 319-334.
• Coleman, B.T. & Hill, R.A. (2014). Living in a landscape of fear: the impact of predation, resource availability and habitat structure on primate range use. Animal Behaviour 88: 165-173.
• Kent, V.T. & Hill, R.A. (2013). The importance of farmland for the conservation of the brown hyaena Parahyaena brunnea. Oryx: The International Journal of Conservation 47(03): 431-440.
• Chase Grey, J.N., Kent, V.T. & Hill, R.A. (2013). Evidence of a high density population of harvested leopards in a montane environment. PLOS ONE 8(12): e82832.
• Smith, R.K., Ryan, E., Morley, E. & Hill, R.A. (2011). Resolving management conflicts: could agricultural land provide the answer for an endangered species in a habitat classified as a World Heritage Site? Environmental Conservation 38(3): 325-333.
• Willems, E.P. & Hill, R.A. (2009). A critical assessment of two species distribution models: a case study of the vervet monkey (Cercopithecus aethiops). Journal of Biogeography 36(12): 2300-2312
• Willems, E.P., Barton, R.A. & Hill, R.A. (2009). Remotely sensed productivity, home range selection and local range use by an omnivorous primate. Behavioral Ecology 20(5): 985-992.
• Hill, R.A (2009). Is isolation the major genetic concern for endangered equids? Animal Conservation 12(6): 518-519
• Willems, E.P. & Hill, R.A. (2009). Predator-specific landscapes of fear and resource distribution: effects on spatial range use. Ecology 90(2): 546–555.
• Hill, R.A., Bentley, R.A. & Dunbar, R.I.M. (2008). Network scaling reveals consistent fractal pattern in hierarchical mammalian societies. Biology Letters 4(6): 748-751.
• Smith, R.K., Marais, A., Chadwick, P., Lloyd, P.H. & Hill, R.A. (2008). Monitoring and management of the endangered Cape mountain zebra Equus zebra zebra in the Western Cape, South Africa. African Journal of Ecology 46(2): 207-213.
• Atrill, M., Gresty, K., Hill R.A. & Barton, R.A. (2008). Red shirt colour is associated with long-term team success in English football. Journal of Sports Sciences 26(6): 577-582.
• Little, A.C & Hill, R.A. (2007). Attribution to red suggests special role in dominance signalling. Journal of Cultural and Evolutionary Psychology 5: 87-94.
• Sellers, W.I., Hill, R.A. & Logan B. (2007). Simulating group decision making in baboons using agent-based modelling. Philosophical transactions of the Royal Society of London 362: 1699-1710.
• Hill, R.A. (2006). Why be diurnal? Or, why not be cathemeral? Folia Primatologica 77: 72-86.
• Hill, R.A. (2006). Thermal constraints on activity scheduling and habitat choice in baboons. American Journal of Physical Anthropology 129(2): 242-249.
• Hill, R.A., Donovan, S. & Koyama, N.F. (2005). Female sexual advertisement reflects resource availability in 20th Century UK society. Human Nature 16: 266-277.
• Hill, R.A. & Barton, R.A. (2005). Red enhances human performance in contests. Nature 435(7040): 293.
• Barton, R.A. & Hill, R.A (2005). Sporting contests: Seeing red? Putting sportswear in context (reply). Nature 437: E10-E11.
• Zhou, W.X., Sornette, D., Hill, R.A. & Dunbar, R.I.M. (2005). Discrete hierarchical organization of social group sizes. Proceedings of the Royal Society B: Biological Sciences 272(1561): 439-444.
• Hill, R.A., Barrett L., Gaynor D., Weingrill T., Dixon P., Payne H. & Henzi S.P. (2004). Day length variation and seasonal analyses of behaviour. South African Journal of Wildlife Research 34: 39-44.
• Hill, R.A., Weingrill T., Barrett L. & Henzi, S.P. (2004). Indices of environmental temperatures for primates in open habitats. Primates 45: 7-13.
• Koyama, N.F., McGain, A. & Hill, R.A. (2004). Self-reported mate preferences and 'femimst' attitudes regarding marital relations. Evolution and Human Behavior 25(5): 327-335.
• Weingrill, T., Lycett, J.E., Barrett, L., Hill, R.A. & Henzi, S.P. (2003). Male consortship behaviour in chacma baboons: The role of demographic factors and female conceptive probabilities. Behaviour 140: 405-427.
• Rae, T.C., Hill, R., Hamada, Y. & Koppe, T. (2003). Clinal variation of maxillary sinus volume in Japanese macaques (_Macaca fuscata_). American Journal of Primatology 59(4): 153-158.
• Hill, R.A. & Dunbar, R.I.M. (2003). Social network size in humans. Human Nature 14(1): 53-72.
• Hill, R.A., Barrett L., Gaynor D., Weingrill T., Dixon P., Payne H. & Henzi S.P. (2003). Day length, latitude and behavioural (in)flexibility in baboons (Papio cynocephalus ursinus). Behavioral Ecology and Sociobiology 53(5): 278-286.
• Henzi, S.P., Barrett, L., Gaynor, D., Greeff, J., Weingrill, T. & Hill, R.A. (2003). Effect of resource competition on the long-term allocation of grooming by female baboons: evaluating Seyfarth's model. Animal Behaviour 66(5): 931-938.
• Hill, R.A. & Dunbar, R.I.M. (2002). Climatic determinants of diet and foraging behaviour in baboons. Evolutionary Ecology 16(6): 579-593.
• Henzi, S.P., Barrett, L., Weingrill, A., Dixon, P. & Hill, R.A. (2000). Ruths amid the alien corn: males and the translocation of female chacma baboons. South African Journal of Science 96(2): 61-62.
• Hill, R.A., Lycett, J.E. & Dunbar, R.I.M. (2000). Ecological and social determinants of birth intervals in baboons. Behavioral Ecology 11(5): 560-564.
• Barrett, L., Henzi, S.P., Weingrill, T., Lycett, J.E. & Hill, R.A. (2000). Female baboons do not raise the stakes but they give as good as they get. Animal Behaviour 59: 763-770.
• Hill, R.A. (1999). Size dependent tortoise predation by baboons at De Hoop Nature Reserve, South Africa. South African Journal of Science 95(3): 123-124.
• Hill, R.A. & Lee, P.C. (1998). Predation risk as an influence on group size in cercopithecoid primates: implications for social structure. Journal of Zoology 245: 447-456.
• Hill, R.A. & Dunbar, R.I.M. (1998). An evaluation of the roles of predation rate and predation risk as selective pressures on primate grouping behaviour. Behaviour 135: 411-430.