ESM 1. Chimpanzee Data Analyses

ESM 1. Chimpanzee data analyses

Insectivory tool use – presence within site

We calculated the opportunity to encounter army ants and termites (Macrotermes) for chimpanzees at Seringbara by multiplying density of insects with chimpanzee encounter probability (Table 1). Encounter probability was based on altitudinal overlap between chimpanzees and insects and calculated by multiplying the proportion of chimpanzee signs with the proportion of army ant trails and Macrotermes mounds recorded across altitude categories [1], and summing values for each altitude category to obtain an overall encounter likelihood value. We plotted encounter likelihood (density x encounter probability) against presence of tool use. Tool use was present for army ants (high encounter likelihood) and absent for Macrotermes (low encounter likelihood). Results are presented in Fig. 1.A.

Table 1. Opportunities for insectivory tool use based on army ant and Macrotermes densities, encounter probabilities and encounter likelihood (density x encounter probability)

Insect species / Density (per km) / Encounter probability / Encounter likelihood / Tool use
Army ants / 0.08 / 0.16 / 0.013 / Yes
Macrotermes / 0.04 / 0.04 / 0.002 / No

Nut cracking tool use – presence across sites

We calculated opportunities for chimpanzees to encounter nut trees by summing nut tree densities for all nut tree species at a study site [1] in order to obtain an overall nut tree density value for each site (trees/ha). We plotted nut tree densities against presence of nut cracking across study sites. Tool use was present only at sites with relatively high nut tree densities (>8 trees/ha). Results are presented in Fig. 1.B.

Insectivory tool use and fruit availability – within site

We assessed the necessity for tool use in insectivory at Seringbara by plotting monthly values for Fruit Availability Index (FAI) against % of feces with ants, a proxy for army ant consumption (Koops et al. Under review, [1]). Army ant consumption was not correlated with monthly availability of ripe fruit (Spearman rank correlation: rs=0.34, N=31, P=0.06). Results are presented in Fig. 1.G.

Tool use and seasonality – across sites

We assessed the relationship between seasonality and the number of subsistence tool use variants. Subsistence tool use variants per study site were obtained from published material [2]. Numbers of dry months (<100 mm rainfall) were obtained from the literature (Table 2). Number of tool use variants was not correlated with number of dry months (Pearson correlation: r=-0.16, N=10, P=0.67). Results are presented in Fig. 1.H.

Table 2. Intensity of seasonality (number of dry months) and subsistence tool use variants for 10 chimpanzee study sites

Study site / Sub species / Dry months / Tool use variants / References
Assirik / P. t. verus / 7 / 4 / [3, 4]
Bossou / P. t. verus / 4 / 13 / [5, 6]
Taï / P. t. verus / 3 / 11 / [4, 7]
Goualougo / P. t. troglodytes / 5 / 11 / [8]
Lopé / P. t. troglodytes / 3 / 4 / [9]
Budongo / P. t. schweinfurthii / 4 / 1 / [10, 11]
Gombe / P. t. schweinfurthii / 6 / 12 / [4, 10]
Kanyawara / P. t. schweinfurthii / 6 / 2 / [4, 12]
Mahale-M / P. t. schweinfurthii / 5 / 5 / [13]
Mahale-K / P. t. schweinfurthii / 5 / 6 / [13]

REFERENCES

[1] Koops, K., McGrew, W.C. & Matsuzawa, T. 2013 Ecology of culture: do environmental factors influence foraging tool use in wild chimpanzees (Pan troglodytes verus)? Anim. Behav. 85, 175-185.

[2] Sanz, C. & Morgan, D. 2007 Chimpanzee tool technology in the Goualougo Triangle, Republic of Congo. J. Hum. Evol. 52, 420-433.

[3] McGrew, W. & Baldwin, P.J. 1981 Chimpanzees in a hot, dry and open habitat: Mt. Assirik, Senegal, West Africa. J. Hum. Evol. 10, 237-244.

[4] Hunt, K.D. & McGrew, W. 2002 Chimpanzees in the dry habitats of Assirik, Senegal and Semliki Wildlife Reserve, Uganda. In Behavioural Diversity in Chimpanzees and Bonobos (eds. C. Boesch, G. Hohmann & L.F. Marchant), pp. 35-51. Cambridge, Cambridge University Press.

[5] Yamakoshi, G. 1998 Dietary responses to fruit scarcity of wild chimpanzees at Bossou, Guinea: possible implications for ecological importance of tool-use. Am. J. Phys. Anthropol. 106, 283-295.

[6] Takemoto, H. 2004 Seasonal change in terrestriality of chimpanzees in relation to microclimate in the tropical forest. Am. J. Phys. Anthropol. 124, 81-92.

[7] Boesch, C. & Boesch-Achermann, H. 2000 The chimpanzees of the Taï Forest: behavioural ecology and evolution. Oxford, Oxford University Press.

[8] Furuichi, T., Sanz, C., Koops, K., Sakamaki, T., Ryu, H., Tokuyama, N. & Morgan, D. In press Why do wild bonobos not use tools like chimpanzees do? Behaviour.

[9] Tutin, C.E.G., White, L.J.T. & Mackanga-Missandzou, A. 1996 Lightning strike burns large forest tree in the Lope Reserve, Gabon. Global Ecology and Biogeography Letters 5, 36-41.

[10] Wallis, J. 2002 Seasonal aspects of reproduction and sexual behavior in two chimpanzee populations: a comparison of Gombe (Tanzania) and Budongo (Uganda). In Behavioural Diversity in Chimpanzees and Bonobos (eds. C. Boesch, G. Hohmann & L.F. Marchant), pp. 181-191. Cambridge, Cambridge University Press.

[11] Reynolds, V. 2005 The chimpanzees of the Budongo Forest: ecology, behavour and conservation. Oxford, Oxford University Press.

[12] Watts, D.P. 2012 Long-Term research on chimpanzee behavioral ecology in Kibale National Park, Uganda. In Long-Term Field Studies of Primates (eds. P.M. Kappeler & D.P. Watts), pp. 313-338. Heidelberg, Dordrecht, London, New York, Springer.

[13] Takasaki, H., Nishida, T., Uehara, S., Norikoshi, K., Kawanaka, K., Takahata, Y., Hiraiwa-Hasegawa, M., Hasegawa, T., Hayaki, H., Masui, K., et al. 1990 Summary of meteorlogical data at Mahale research camp, 1973-1988. In The chimpanzees of the Mahale Mountains: sexual and life history strategies (ed. T. Nishida), pp. 291-300. Tokyo, University of Tokyo Press.

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