Eduardo B. Ottoni

EthoLog 2.2: a tool for the transcription and timing of behavior observation sessions.

EthoLog is a tool that aids in the transcription and timing of behavior observation sessions—experimental or naturalistic, from video/audio tapes or registering real time. It was created with Visual Basic and runs on Windows (3.x / 9x). The user types the key codes for the predefined behavioral categories, and EthoLog registers their sequence and timing and saves the resulting data in ASCII output files. A sequential analysis matrix can be generated from the sequential data. The output files may be edited, converted to plain text files for printing, or exported to a spreadsheet program, such as MS Excel, for further analyses.

Semifree-ranging tufted capuchins (Cebus apella) spontaneously use tools to crack open nuts.

Naturalistic studies on tool use by nonhuman primates have focused almost exclusively on Old World monkeys or hominoids. We studied the cracking of Syagrus nuts with the aid of stones by a group of semifree-ranging capuchins living in a reforested area (Tietê Ecological Park, São Paulo, Brazil). Our data are from direct observation and from mapping nut-cracking site utilization. All adults, subadults and juveniles (plus one infant) crack nuts, but individual differences in frequency and proficiency are marked. Juveniles do most of the nut-cracking, but adults are, on average, more efficient; the frequency of inept stone manipulation decreases with age. About 10% of the nut-cracking episodes were watched by other individuals—mostly infants and juveniles, suggesting a role for observational learning, even if restricted to stimulus enhancement.

Watching the best nutcrackers: what capuchin monkeys (Cebus apella) know about others’ tool-using skills

The present work is part of a decade-long study on the spontaneous use of stones for cracking hard-shelled nuts by a semi-free-ranging group of brown capuchin monkeys (Cebus apella). Nutcracking events are frequently watched by other individuals - usually younger, less proficient, and that are well tolerated to the point of some scrounging being allowed by the nutcracker. Here we report findings showing that the choice of observational targets is an active, non-random process, and that observers seem to have some understanding of the relative proficiency of their group mates, preferentially watching the more skilled nutcrackers, which enhances not only scrounging payoffs, but also social learning opportunities.

Kinematics and Energetics of Nut-Cracking in Wild Capuchin Monkeys (Cebus libidinosus) in Piaui´, Brazil

Wild bearded capuchins (Cebus libidinosus, quadrupedal, medium-sized monkeys) crack nuts using large stones. We examined the kinematics and energetics of the nut-cracking action of two adult males and two adult females. From a bipedal stance, the monkeys raised a heavy hammer stone (1.46 and 1.32 kg, from 33 to 77% of their body weight) to an average height of 0.33 m, 60% of body length. Then, they rapidly lowered the stone by flexing the lower extremities and the trunk until the stone contacted the nut. A hit consisting of an upward phase and a downward phase averaged 0.74 s in duration. The upward phase lasted 69% of hit duration. All subjects added discernable energy to the stone in the downward phase. The monkeys exhibited individualized kinematic strategies, similar to those of human weight lifters. Capuchins illustrate that human-like bipedal stance and large body size are unnecessary to break tough objects from a bipedal position. The phenomenon of bipedal nut-cracking by capuchins provides a new comparative reference point for discussions of percussive tool use and bipedality in primates.

Ontogeny of manipulative behavior and nut-cracking in young tufted capuchin monkeys (Cebus apella): a perception-action perspective.

How do capuchin monkeys learn to use stones to crack open nuts? Perception-action theory posits that individuals explore producing varying spatial and force relations among objects and surfaces, thereby learning about affordances of such relations and how to produce them. Such learning supports the discovery of tool use. We present longitudinal developmental data from semifree-ranging tufted capuchin monkeys (Cebus apella) to evaluate predictions arising from Perception-action theory linking manipulative development and the onset of tool-using. Percussive actions bringing an object into contact with a surface appeared within the first year of life. Most infants readily struck nuts and other objects against stones or other surfaces from 6 months of age, but percussive actions alone were not sufficient to produce nut-cracking sequences. Placing the nut on the anvil surface and then releasing it, so that it could be struck with a stone, was the last element necessary for nut-cracking to appear in capuchins. Young chimpanzees may face a different challenge in learning to crack nuts: they readily place objects on surfaces and release them, but rarely vigorously strike objects against surfaces or other objects. Thus the challenges facing the two species in developing the same behavior (nut-cracking using a stone hammer and an anvil) may be quite different. Capuchins must inhibit a strong bias to hold nuts so that they can release them; chimpanzees must generate a percussive action rather than a gentle placing action. Generating the right actions may be as challenging as achieving the right sequence of actions in both species. Our analysis suggests a new direction for studies of social influence on young primates learning sequences of actions involving manipulation of objects in relation to surfaces.

Means to an end: Neotropical parrots manage to pull strings to meet their goals

Although parrots share with corvids and primates many of the traits believed to be associated with advanced cognitive processing, knowledge of parrot cognition is still limited to a few species, none of which are Neotropical. Here we examine the ability of three Neotropical parrot species (Blue-Fronted Amazons, Hyacinth and Lear’s macaws) to spontaneously solve a novel physical problem: the string-pulling test. The ability to pull up a string to obtain out-of-reach food has been often considered a cognitively complex task, as it requires the use of a sequence of actions never previously assembled, along with the ability to continuously monitor string, food and certain body movements. We presented subjects with pulling tasks where we varied the spatial relationship between the strings, the presence of a reward and the physical contact between the string and reward to determine whether (1) string-pulling is goal-oriented in these parrots, (2) whether the string is recognized as a means to obtain the reward and (3) whether subjects can visually determine the continuity between the string and the reward, selecting only those strings for which no physical gaps between string and reward were present. Our results show that some individuals of all species were able to use the string as a means to reach a specific goal, in this case, the retrieval of the food treat. Also, subjects from both macaw species were able to visually determine the presence of physical continuity between the string and reward, making their choices consistently with the recognition that no gaps should be present between the string and the reward. Our findings highlight the potential of this taxonomic group for the understanding of the underpinnings of cognition in evolutionarily distant groups such as birds and primates.

Cognition in an ever-changing world: climatic variability is associated with brain size in Neotropical parrots.

Research on the conditions favoring the evolution of complex cognition and its underlying neural structures has increasingly stressed the role of environmental variability. These studies suggest that the ability to learn, behave flexibly and innovate would be favored under unpredictable variations in the availability of resources, as it would enable organisms to adjust to novel conditions. Despite the growing number of studies based on the idea that larger-brained organisms would be better prepared to cope with environmental challenges, direct testing of the association between brain size and environmental variability per se remains scant. Here we focus on Neotropical parrots as our model group and test the hypothesis that if relatively larger brains were favored in climatically variable environments, larger-brained species should currently tolerate a higher degree of environmental uncertainty. Although we show that there are also other factors underlying the dynamics of brain size variation in this group, our results support the hypothesis that proportionally larger-brained species are more tolerant to climatic variability, both on a temporal and spatial scale. Additionally, they suggest that the differences in relative brain size among Neotropical parrots represent multiple, recent events in the evolutionary history of the group, and are particularly tied to an increased dependence on more open and climatically unstable habitats. As this is the first study to present evidence of the link between brain size and climatic variability in birds, our findings provide a step towards understanding the potential benefits underlying variation in brain size and the maintenance of highly enlarged brains in this and other groups.

Physical properties of palm fruits processed with tools by wild bearded capuchins (Cebus libidinosus).

Habitually, capuchin monkeys access encased hard foods by using their canines and premolars and/or by pounding the food on hard surfaces. Instead, the wild bearded capuchins (Cebus libidinosus) of Boa Vista (Brazil) routinely crack palm fruits with tools. We measured size, weight, structure, and peak‐force‐at‐failure of the four palm fruit species most frequently processed with tools by wild capuchin monkeys living in Boa Vista. Moreover, for each nut species we identify whether peak‐force‐at‐failure was consistently associated with greater weight/volume, endocarp thickness, and structural complexity. The goals of this study were (a) to investigate whether these palm fruits are difficult, or impossible, to access other than with tools and (b) to collect data on the physical properties of palm fruits that are comparable to those available for the nuts cracked open with tools by wild chimpanzees. Results showed that the four nut species differ in terms of peak‐force‐at‐failure and that peak‐force‐at‐failure is positively associated with greater weight (and consequently volume) and apparently with structural complexity (i.e. more kernels and thus more partitions); finally for three out of four nut species shell thickness is also positively associated with greater volume. The finding that the nuts exploited by capuchins with tools have very high resistance values support the idea that tool use is indeed mandatory to crack them open. Finally, the peak‐force‐at‐failure of the piassava nuts is similar to that reported for the very tough panda nuts cracked open by wild chimpanzees; this highlights the ecological importance of tool use for exploiting high resistance foods in this capuchin species. Am. J. Primatol. 70:884–891, 2008.

How wild bearded capuchin monkeys select stones and nuts to minimize the number of strikes per nut cracked

Wild bearded capuchin monkeys, Cebus libidinosus, use stone tools to crack palm nuts to obtain the kernel. In five experiments, we gave 10 monkeys from one wild group of bearded capuchins a choice of two nuts differing in resistance and size and/or two manufactured stones of the same shape, volume and composition but different mass. Monkeys consistently selected the nut that was easier to crack and the heavier stone. When choosing between two stones differing in mass by a ratio of 1.3:1, monkeys frequently touched the stones or tapped them with their fingers or with a nut. They showed these behaviours more frequently before making their first selection of a stone than afterward. These results suggest that capuchins discriminate between nuts and between stones, selecting materials that allow them to crack nuts with fewer strikes, and generate exploratory behaviours to discriminate stones of varying mass. In the final experiment, humans effectively discriminated the mass of stones using the same tapping and handling behaviours as capuchins. Capuchins explore objects in ways that allow them to perceive invariant properties (e.g. mass) of objects, enabling selection of objects for specific uses. We predict that species that use tools will generate behaviours that reveal invariant properties of objects such as mass; species that do not use tools are less likely to explore objects in this way. The precision with which individuals can judge invariant properties may differ considerably, and this also should predict prevalence of tool use across species.

Distribution of potential suitable hammers and transport of hammer tools and nuts by wild capuchin monkeys

Selection and transport of objects to use as tools at a distant site are considered to reflect planning. Ancestral humans transported tools and tool-making materials as well as food items. Wild chimpanzees also transport selected hammer tools and nuts to anvil sites. To date, we had no other examples of selection and transport of stone tools among wild nonhuman primates. Wild bearded capuchins (Cebus libidinosus) in Boa Vista (Piauí, Brazil) routinely crack open palm nuts and other physically well-protected foods on level surfaces (anvils) using stones (hammers) as percussive tools. Here we present indirect evidence, obtained by a transect census, that stones suitable for use as hammers are rare (study 1) and behavioral evidence of hammer transport by twelve capuchins (study 2). To crack palm nuts, adults transported heavier and harder stones than to crack other less resistant food items. These findings show that wild capuchin monkeys selectively transport stones of appropriate size and hardness to use as hammers, thus exhibiting, like chimpanzees and humans, planning in tool-use activities.