Primate archaeology 3.0.

The new field of primate archaeology investigates the technological behavior and material record of nonhuman primates, providing valuable comparative data on our understanding of human technological evolution. Yet, paralleling hominin archaeology, the field is largely biased toward the analysis of lithic artifacts. While valuable comparative data have been gained through an examination of extant nonhuman primate tool use and its archaeological record, focusing on this one single aspect provides limited insights. It is therefore necessary to explore to what extent other non-technological activities, such as non-tool aided feeding, traveling, social behaviors or ritual displays, leave traces that could be detected in the archaeological record. Here we propose four new areas of investigation which we believe have been largely overlooked by primate archaeology and that are crucial to uncovering the full archaeological potential of the primate behavioral repertoire, including that of our own: (1) Plant technology; (2) Archaeology beyond technology; (3) Landscape archaeology; and (4) Primate cultural heritage. We discuss each theme in the context of the latest developments and challenges, as well as propose future directions. Developing a more "inclusive" primate archaeology will not only benefit the study of primate evolution in its own right but will aid conservation efforts by increasing our understanding of changes in primate-environment interactions over time.

Cultural variation between neighbouring communities of chimpanzees at Gombe, Tanzania.

Comparative animal studies have revealed the existence of inter-group differences in socially learned behaviours - so-called cultural variations. However, most research has drawn on geographically and thus environmentally separated populations, rendering it difficult to exclude genetic or ecological influences. To circumvent this problem, the behaviour of neighbouring groups from the same population can be juxtaposed - an approach which in wild chimpanzees (Pan troglodytes) has revealed cultural differences in the use of nut-cracking and ant-dipping tools. Here I apply archaeological methods to extend this approach to compare the qualities of termite fishing tools used by wild chimpanzees by comparing the neighbouring Kasekela and Mitumba communities at Gombe Stream National Park, Tanzania. While no identifiable differences existed between the available plant species and associated vegetal components, members of the Kasekela community selected a larger array of raw materials and manufactured significantly longer and wider tools compared with the Mitumba community. Thus, cultural knowledge is reflected in differentiated behaviour on a small spatial scale. This study emphasizes the use of archaeological methods to identify cultural variation among living chimpanzee communities, adding to the growing research operating within the new field of Primate Archaeology.

Possible mineral contributions to the diet and health of wild chimpanzees in three East African forests.

We present new data on the ingestion of minerals from termite mound soil by East African chimpanzees (Pan troglodytes schweinfurthii) living in the Budongo Forest Reserve, Uganda, the Gombe National Park and the Mahale Mountains National Park, Tanzania. Termite mound soil is here shown to be a rich source of minerals, containing high concentrations of iron and aluminum. Termite mound soil is not, however, a source of sodium. The concentrations of iron and aluminum are the highest yet found in any of the mineral sources consumed. Levels of manganese and copper, though not so high as for iron and aluminum, are also higher than in other dietary sources. We focus on the contribution of termite mound soil to other known sources of mineral elements consumed by these apes, and compare the mineral content of termite soil with that of control forest soil, decaying wood, clay, and the normal plant-based chimpanzee diet at Budongo. Samples obtained from Mahale Mountains National Park and Gombe National Park, both in Tanzania, show similar mineral distribution across sources. We suggest three distinct but related mechanisms by which minerals may come to be concentrated in the above-mentioned sources, serving as potentially important sources of essential minerals in the chimpanzee diet.

Scars on plants sourced for termite fishing tools by chimpanzees: Towards an archaeology of the perishable.

Chimpanzees are well-studied, but raw material acquisition for tool use is still poorly understood as sources are difficult to trace. This study pioneers the use of information that can be gleaned from plant scars made by chimpanzees while they source vegetation parts to manufacture termite fishing tools. Source plant species, raw material types and locations relative to targeted termite mounds were recorded for populations at Gombe, Issa, and Mahale in western Tanzania. Recovered bark, twig, and vine tools were traced to 29 plant species, while grass sources were indeterminable. Bark extraction scars remained detectable for months, and thus possibly for as long as the plant is alive, while twig and vine scars preserved for a few weeks only. Scars preserve better than tools, given that twice as many plant species could be linked to the former than to the latter. Some source species were exploited across all sites for the same type of tool material, while two species were sourced for different types. Compared to apes at Gombe and Mahale, Issa chimpanzees carried material from twice as far away, perhaps because the Issa habitat is more open and dry, which entails greater distances between suitable raw material sources and targeted mounds. Site-specific tools were based on different raw materials, in two cases sourced from the same species, which could suggest learned preferences for particular tool material. "Archaeology of the perishable" as pioneered in this study broadens the methodological approach of the wider field of primate archaeology to include reconstructions of past animal behavior associated with the production of plant based tools.

Primate archaeology evolves.

Since its inception, archaeology has traditionally focused exclusively on humans and our direct ancestors. However, recent years have seen archaeological techniques applied to material evidence left behind by non-human animals. Here, we review advances made by the most prominent field investigating past non-human tool use: primate archaeology. This field combines survey of wild primate activity areas with ethological observations, excavations and analyses that allow the reconstruction of past primate behaviour. Because the order Primates includes humans, new insights into the behavioural evolution of apes and monkeys also can be used to better interrogate the record of early tool use in our own, hominin, lineage. This work has recently doubled the set of primate lineages with an excavated archaeological record, adding Old World macaques and New World capuchin monkeys to chimpanzees and humans, and it has shown that tool selection and transport, and discrete site formation, are universal among wild stone-tool-using primates. It has also revealed that wild capuchins regularly break stone tools in a way that can make them difficult to distinguish from simple early hominin tools. Ultimately, this research opens up opportunities for the development of a broader animal archaeology, marking the end of archaeology's anthropocentric era.

Raw material procurement for termite fishing tools by wild chimpanzees in the Issa valley, Western Tanzania.

OBJECTIVES: Chimpanzee termite fishing has been studied for decades, yet the selective processes preceding the manufacture of fishing tools remain largely unexplored. We investigate raw material selection and potential evidence of forward planning in the chimpanzees of Issa valley, western Tanzania. MATERIALS AND METHODS: Using traditional archaeological methods, we surveyed the location of plants from where chimpanzees sourced raw material to manufacture termite fishing tools, relative to targeted mounds. We measured raw material abundance to test for availability and selection. Statistics included Chi-Squared, two-tailed Wilcoxon, and Kruskall-Wallace tests. RESULTS: Issa chimpanzees manufactured extraction tools only from bark, despite availability of other suitable materials (e.g., twigs), and selected particular plant species as raw material sources, which they often also exploit for food. Most plants were sourced 1-16 m away from the mound, with a maximum of 33 m. The line of sight from the targeted mound was obscured for a quarter of these plants. DISCUSSION: The exclusive use of bark tools despite availability of other suitable materials indicates a possible cultural preference. The fact that Issa chimpanzees select specific plant species and travel some distance to source them suggests some degree of selectivity and, potentially, forward planning. Our results have implications for the reconstruction of early hominin behaviors, particularly with regard to the use of perishable tools, which remain archaeologically invisible.

Sustained myrmecophagy in Nigerian chimpanzees: Preferred or fallback food?

OBJECTIVE: At some sites across Africa, chimpanzees consume army ants, often aided by plant tools, although consumption frequencies vary greatly. Other populations do not eat these insects at all, despite apparent abundance. The relative importance of this type of myrmecophagy for chimpanzee diet therefore remains unclear. We investigate if army ants constitute a preferred food or a fallback resource for chimpanzees at Gashaka, Nigeria, where army ants are consumed much more frequently than elsewhere. METHODS: Long-term records on temporal variation of climate and availability of fruit as the chimpanzees' preferred food are compared with rates of recovered army ant dipping wands and army ant remains in feces. RESULTS: Despite strict seasonality of rainfall and fruit abundance, myrmecophagy does not negatively correlate with fruit availability. Instead, army ant eating is sustained year round at high levels, with 44% of feces containing remains. CONCLUSIONS: Results contradict the fallback hypothesis and support the hypothesis that ants are a preferred food. Nevertheless, compared with fruit, ant-meals can normally provide only negligible amounts of nutrients. At Gashaka, however, nutritional yield may be significant, given that ant-dipping sessions provide on average 13 mg of dry weight to a chimpanzee. The species exclusively eaten here, Dorylus rubellus, might be particularly aggressive, thus resulting in greater harvesting success than elsewhere. Army ants may hence serve as a diet supplement or complement in terms of macro- or micronutrients.

Wild capuchin monkeys adjust stone tools according to changing nut properties.

Animals foraging in their natural environments need to be proficient at recognizing and responding to changes in food targets that affect accessibility or pose a risk. Wild bearded capuchin monkeys (Sapajus libidinosus) use stone tools to access a variety of nut species, including otherwise inaccessible foods. This study tests whether wild capuchins from Serra da Capivara National Park in Brazil adjust their tool selection when processing cashew (Anacardium spp.) nuts. During the ripening process of cashew nuts, the amount of caustic defensive substance in the nut mesocarp decreases. We conducted field experiments to test whether capuchins adapt their stone hammer selection to changing properties of the target nut, using stones of different weights and two maturation stages of cashew nuts. The results show that although fresh nuts are easier to crack, capuchin monkeys used larger stone tools to open them, which may help the monkeys avoid contact with the caustic hazard in fresh nuts. We demonstrate that capuchin monkeys are actively able to distinguish between the maturation stages within one nut species, and to adapt their foraging behaviour accordingly.

Apes finding ants: Predator-prey dynamics in a chimpanzee habitat in Nigeria.

Some chimpanzee populations prey upon army ants, usually with stick tools. However, how their prey's subterranean nesting and nomadic lifestyle influence the apes' harvesting success is still poorly understood. This is particularly true for chimpanzees (Pan troglodytes ellioti) at Gashaka/Nigeria, which consume army ants (Dorylus rubellus) with much higher frequency than at other sites. We assessed various harvesting and search options theoretically available to the apes. For this, we reconstructed annual consumption patterns from feces and compared the physical characteristics of exploited ant nests with those that were not targeted. Repeated exploitation of a discovered nest is viable only in the short term, as disturbed colonies soon moved to a new site. Moreover, monitoring previously occupied nest cavities is uneconomical, as ants hardly ever re-used them. Thus, the apes have to detect new nests regularly, although colony density is relatively low (1 colony/1.3 ha). Surprisingly, visual search cues seem to be of limited importance because the probability of a nest being exploited was independent of its conspicuousness (presence of excavated soil piles, concealing leaf-litter or vegetation). However, chimpanzees preferentially targeted nests in forests or at the base of food trees, that is, where the apes spend relatively more time and/or where ant colony density is highest. Taken together, our findings suggest that, instead of employing a search strategy based on visual cues or spatial memory, chimpanzee predation on army ants contains a considerable opportunistic element.

Obtaining raw material: plants as tool sources for Nigerian chimpanzees.

We investigated the acquisition of plant materials from which Nigerian chimpanzees manufacture wooden tools to harvest insects and honey from nests of army ants, honey bees and stingless bees. Slender trunks of juvenile trees and branches are most commonly used, and bendable vines rarely, probably reflecting the need to work with relatively sturdy tools to extract resources. While several tools are sometimes sourced from the same plant, there is also evidence for a depletion effect, as multiple tool sources at the same site are often spaced several metres apart. Identified tool sources belong to 27 species of at least 13 families. Honey-gathering implements are often chewed upon by chimpanzees. Interestingly, twigs of the most commonly used honey-gathering species possess antibacterial propensities and are favoured by Nigerians as chewing sticks. This suggests that extractive tools might possess associated medicinal or stimulatory properties. We do not know if chimpanzees actively select specific plant parts or species as we cannot compare observed with expected frequencies. Nevertheless, about three quarters of tools are picked from plants more than 6 m away from the extraction site, potentially indicating some degree of forward planning.