ESM 2. Orang-utan data analyses

Tree hole tool use – presence across sites

We estimated the opportunity for innovation of tree-hole tool use in two Sumatran sites (i.e. Suaq, Ketambe). We found that the innovation index (orang-utan density x tree hole density) was over 4 times higher at the site with tool use present than the site without it (Table 1). Most of this tool use concerns honey from stingless bees. Data are from published work [1]. Results are presented in Figure 1.C.

Table 1. Opportunities for innovation of tree-hole tool use at Suaq and Ketambe

Tools present / Tools absent
Suaq / Ketambe
Inhabited tree holes/km / 8.85 / 4.98
Proportion with bees / 0.09 / 0.05
Orang-utan density/km2 / 7 / 5
Innovation index / 5.6 / 1.25

Neesia tool use – presence across sites

We estimated the opportunity for innovation of Neesia tool use (size of local Neesia population x N orang-utans in Neesia population) in Sumatran and Bornean orang-utan populations. Tool use is more effective than breaking open. Data are from van Schaik (unpublished) for Sumatra (gray symbols), and from published work [2, 3] and personal communication for Borneo (black symbols). This method treats each local population as an isolated unit, which generally works, but not always. Case in point: Batang Toru (open symbol) is a small population, which until recently was next to a large swamp population with many Neesia trees (where Neesia tool use was almost certainly established). We indicated with the arrow where we believe it would have been placed had we visited the site 20 years earlier. Results are presented in Figure 1.D.

Tree hole tool use and fruit availability – within site

For Suaq, we examined the effect of ripe fruit abundance (% trees with ripe fruit), as taken from a phenology plot with 350 trees in the central swamp area, on the rate of use of tree-hole tools (per 100 focal follow hours) for the focal females in the population. The rate of tree-hole tools was not correlated with the % trees with ripe fruit (Spearman rank correlation: rs=0.17, N=49, P=0.252). Results are presented in Figure 1.I.

Tool use and cambium feeding – across sites

We examined the number of subsistence tools used in a population of orang-utans in relation to need for technology (as proxied by the maximum monthly percentage of feeding on cambium). Data are from published work [4, 5], and additional information on Tuanan (M. van Noordwijk, pers. com.). Number of subsistence tool use variants was not correlated with maximum % cambium feeding (Spearman rank correlation: rs=-0.65, N=8, P=0.081). Results are presented in Figure 1.J.

REFERENCES

[1] Fox, E.A., van Schaik, C.P., Sitompul, A.F. & Wright, D.N. 2004 Intra- and interpopulational differences in orangutan (Pongo pygmaeus) activity and diet: implications for the invention of tool use. Am. J. Phys. Anthropol. 125, 162-174.

[2] van Schaik, C.P. & Knott, C.D. 2001 Geographic variation in tool use on Neesia fruits in orangutans. Am. J. Phys. Anthropol. 114, 331-342.

[3] Kanamori, T., Kuze, N., Bernard, H., Malim, T.P. & Kohshima, S. 2010 Feeding ecology of Bornean orangutans (Pongo pygmaeus morio) in Danum Valley, Sabah, Malaysia: a 3-year record including two mast fruitings. Am. J. Primatol. 72, 820-840.

[4] Wich, S.A., Geurts, M.L., Utami-Atmoko, S.S., Mitra Setia, T. & Djoyosudharmo, S. 2006 Dietary and energetic responses of Pongo abelii to fruit availability fluctuations Int. J. Primatol. 27, 1535-1550.

[5] Wich, S.A., Shumaker, R.W., Perkins, L. & de Vries, H. 2009 Captive and wild orangutan (Pongo sp.) survivorship: a comparison and the influence of management. Am. J. Primatol. 71, 680-686.

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