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1.  Stone Anvil Damage by Wild Bearded Capuchins (Sapajus libidinosus) during Pounding Tool Use: A Field Experiment 
PLoS ONE  2014;9(11):e111273.
We recorded the damage that wild bearded capuchin monkeys (Sapajus libidinosus) caused to a sandstone anvil during pounding stone tool use, in an experimental setting. The anvil was undamaged when set up at the Fazenda Boa Vista (FBV) field laboratory in Piauí, Brazil, and subsequently the monkeys indirectly created a series of pits and destroyed the anvil surface by cracking palm nuts on it. We measured the size and rate of pit formation, and recorded when adult and immature monkeys removed loose material from the anvil surface. We found that new pits were formed with approximately every 10 nuts cracked, (corresponding to an average of 38 strikes with a stone tool), and that adult males were the primary initiators of new pit positions on the anvil. Whole nuts were preferentially placed within pits for cracking, and partially-broken nuts outside the established pits. Visible anvil damage was rapid, occurring within a day of the anvil's introduction to the field laboratory. Destruction of the anvil through use has continued for three years since the experiment, resulting in both a pitted surface and a surrounding archaeological debris field that replicate features seen at natural FBV anvils.
doi:10.1371/journal.pone.0111273
PMCID: PMC4221011  PMID: 25372879
2.  Wild Bearded Capuchin Monkeys (Sapajus libidinosus) Strategically Place Nuts in a Stable Position during Nut-Cracking 
PLoS ONE  2013;8(2):e56182.
Humans can use hand tools smoothly and effectively in varying circumstances; in other words, skillfully. A few other species of primates crack encased foods using hammer tools and anvils. Are they skilled? Positioning the food on the anvil so that it does not fall off when struck is a component of skilled cracking. We discovered that bearded capuchin monkeys deliberately place palm nuts in a relatively stable position on the anvil before striking them. In the first experiment, we marked the meridians of palm nuts where they stopped when rolled on a flat surface (“Stop meridian”). We videotaped monkeys as they cracked these nuts on an anvil. In playback we coded the position of the Stop meridian prior to each strike. Monkeys typically knocked the nuts on the anvil a few times before releasing them in a pit. They positioned the nuts so that the Stop meridian was within 30 degrees of vertical with respect to gravity more often than expected, and the nuts rarely moved after the monkeys released them. In the second experiment, 14 blindfolded people (7 men) asked to position marked nuts on an anvil as if to crack them reliably placed them with the Stop meridian in the same position as the monkeys did. In the third experiment, two people judged that palm nuts are most bilaterally symmetric along a meridian on, or close to, the Stop meridian. Thus the monkeys reliably placed the more symmetrical side of the nuts against the side of the pit, and the nuts reliably remained stationary when released. Monkeys apparently used information gained from knocking the nut to achieve this position. Thus, monkeys place the nuts skillfully, strategically managing the fit between the variable nuts and pits in the anvil, and skilled placement depends upon information generated by manual action.
doi:10.1371/journal.pone.0056182
PMCID: PMC3584076  PMID: 23460793
3.  How tufted capuchin monkeys (Cebus apella spp) and common chimpanzees (Pan troglodytes) align objects to surfaces: Insights into spatial reasoning and implications for tool use 
American journal of primatology  2011;73(10):1012-1030.
This report addresses phylogenetic variation in a spatial skill that underlies tool use: aligning objects to a feature of a surface. Fragaszy and Cummins-Sebree’s [2005] model of relational spatial reasoning and Skill Development and Perception-Action theories guided the design of the study. We examined how capuchins and chimpanzees place stick objects of varying shapes into matching grooves on a flat surface. Although most individuals aligned the long axis of the object with the matching groove more often than expected by chance, all typically did so with poor precision. Some individuals managed to align a second feature, and only one (a capuchin monkey) achieved above-chance success at aligning three features with matching grooves. Our findings suggest that capuchins and chimpanzees do not reliably align objects along even one axis, and that neither species can reliably or easily master object placement tasks that require managing two or more spatial relations concurrently. Moreover, they did not systematically vary their behavior in a manner that would aid discovery of the affordances of the stick-surface combination beyond sliding the stick along the surface (which may have provided haptic information about the location of the groove). These limitations have profound consequences for the forms of tool use we can expect these individuals to master.
doi:10.1002/ajp.20966
PMCID: PMC3166442  PMID: 21608008
Allocentric; Egocentric; spatial reasoning; object manipulation; alignment; tool use
4.  Development of Maze Navigation by Tufted Capuchins (Cebus apella) 
Behavioural processes  2010;86(2):206-215.
Theories of spatial navigation hypothesize that animals use vector or topological information to choose routes, often including detours, to move objects or themselves to goals. We assessed adult capuchin monkeys’ (Cebus apella) navigation through 192 virtual 2-dimensional mazes that incorporated detour problems. Six monkeys initially were significantly less likely to choose the correct paths when detours were required than when not. Three of the six monkeys repeatedly practiced the 192 mazes to asymptotic mastery; the other three did not practice the mazes again. In a subsequent transfer test, each monkey made correct choices equivalently often on familiar and novel mazes, which suggests that they used general planning skills for maze navigation. Of the three monkeys that practiced the 192 maze-set repeatedly, one efficiently detoured and the other two significantly improved detouring compared to their initial performance. Two monkeys, contrary to their performance when completing the 192 maze-set for the first time, made correct choices at the same rate as chimpanzees. Some evidence suggested that two monkeys used topological information, but utilization of vector information was obvious for all monkeys. Our findings suggest that the boundaries of any individual’s navigational abilities are not predicted by species, but depend on experience.
doi:10.1016/j.beproc.2010.11.006
PMCID: PMC3434124  PMID: 21138761
detour; planning; spatial learning; topological organization; vector information; cognition
5.  Critically endangered blonde capuchins fish for termites and use new techniques to accomplish the task 
Biology Letters  2011;7(4):532-535.
We report the spontaneous modification and use of sticks to fish for termites, above the ground, in wild blonde capuchins (Cebus flavius). These critically endangered Neotropical primates inhabit remnants of the Atlantic Forest. They used two previously undescribed techniques to enhance their termite capture success: nest tapping and stick rotation. The current ecologically based explanation for tool use in wild capuchins (i.e. terrestrial habits and bipedalism) must be viewed cautiously. Instead, remarkable manual skills linked to a varied diet seem important in promoting tool use in different contexts. The repertoire of tool-using techniques employed by wild capuchins has been expanded, highlighting the behavioural versatility in this genus.
doi:10.1098/rsbl.2011.0034
PMCID: PMC3130233  PMID: 21389018
tool use; manual skills; cognition; blonde capuchins; primates

Results 1-5 (5)