Moving.

Examples of realized scientific careers can provide ideas and inspiration for others aiming to pursue such careers. Here I recount in brief the story of my long career in primatology (1973 to the present), focusing on one enduring theme in my research: the nature and genesis of goal-directed action (evident in movement). The story begins in graduate school, passes through developing my own laboratory, on to pursuing a spectrum of studies with mentees and collaborators, developing a theoretical explanatory framework for goal-directed action that I think holds promise for the field as a whole, and ends with an exciting field project that seems a suitable finale to my career. I mention the value to me, the field, and society of participation in scientific societies, including the American Society of Primatologists, throughout my career.

Adaptable navigation in bull ants (Myrmecia midas).

In an early scientific description of navigation (finding one's way from a known location to a known destination) in an arthropod, Charles Turner, one of comparative psychology's staunchest early proponents of studying individual variation. The field of comparative psychology has caught up with Charles Turner. In this essay, the author presents an overview of the results of previous studies which suggest that several species of ants use vision effectively to navigate in three dimensions, in daylight, and in darkness. Bull ants, a species that navigates in dim light, have large compound eyes containing receptors that are sensitive to ultraviolet (UV), blue, and green regions of the electromagnetic spectrum. Islam et al.'s findings illustrate a very general point about behavior that comparative psychologists do (and should continue to) take seriously, theoretically, and empirically. When we take the time to look closely, the behavior of individuals varies in biologically and psychologically important ways, no matter the size of their bodies or nervous systems. The adaptability of individuals arises from variation within the individual over time, manifest in this study as the adoption of novel routes as circumstances required. The adaptability of populations arises from variation across individuals, evident in this study in ants that learned to travel directly to the edge of the barrier and ants that learned to travel directly to the barrier, then make a right-angle turn to travel along it to an edge. The sources and consequences of behavioral variability, within and across individuals, and its manifestations across species, must remain core concerns for comparative psychology, as they were for Charles Turner more than 100 years ago. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Stone tools improve diet quality in wild monkeys.

Tool use is a fundamental feature of human evolution. Stone tools are in the archaeological record from 3.4 Ma, even before Homo,1 and the use of stone tools probably predated the split between hominins and panins.2 Using tools (hereafter, tooling cf Fragaszy and Mangalam3) is hypothesized to have improved hominins' foraging efficiency or access to high-quality foods.4-7 This hypothesis is supported if feeding with tools positively contributes to diet quality in extant non-human primates or if foraging efficiency is increased by tooling. However, the contribution of tooling to non-human primates' foraging success has never been investigated through a direct analysis of nutritional ecology.8,9 We used multi-dimensional nutritional geometry to analyze energy and macronutrients (nonstructural carbohydrates, lipids, and protein) in the diets of wild capuchin monkeys (Sapajus libidinous) that routinely crack palm nuts with stone hammers.10,11 We show that eating nuts obtained through tooling helps monkeys to achieve more consistent dietary intakes. Tooling increased the net energy gain by 50% and decreased the proportion of fiber ingested by 7%. Tooling also increased the daily non-protein energy intake. By contrast, protein intake remained constant across foraging days, suggesting a pattern of macronutrient regulation called protein prioritization, which is also found in contemporary humans.8,9 In addition, tooling reduced dispersion in the ratio of protein to non-protein energy, suggesting a role in macronutrient balancing. Our findings suggest that tooling prior to tool making could have substantially increased the nutritional security of ancestral hominins, sowing the seeds for cultural development.5,7 VIDEO ABSTRACT.

Rules and metarules: Adult cotton-top tamarins (Saguinus oedipus) and 5-year-old children (Homo sapiens) can master both.

Developmental psychologists have noted a similar timeline of change for children's use of different perspectives about the same objects or events, as in the use of different labels for the same object, an aspect of language, and in understanding other's knowledge or beliefs, an aspect of social cognition as reviewed in the study by Neiworth et al. Comparative psychologists are interested to know what cognitive flexibility looks like in other species and how such variation relates to life history, ecology, and phylogeny. The general pattern of results to date indicates that monkeys can master both intra- and interdimensional shifts, but intradimensional shifts are learned far more quickly than interdimensional shifts (reviewed in the study by Neiworth et al, 2022). Neiworth et al. report that they have conducted exactly this kind of comparative study: They examined cognitive flexibility in adult cotton-top tamarins and human children in three age groups as they participated in a modified version of the Dimensional Change Card Sort (DCCS). Neiworth et al.'s study offers an example of careful consideration of one such possibility: that of using the experimenter's postural orientation to the cards as an inadvertent aid. Here the authors had the benefit of prior work showing that tamarins follow human-provided cues to make a spatially discriminated choice only if the experimenter's head, body, and eyes oriented to a particular location. Thus, in this study, the experimenter kept their head and body centered in the testing space between the two cards and looked at a point on the wall directly behind the midpoint of the testing tray. But the DCCS task, in abstract form, has potentially broader comparative value than to examine cognitive flexibility in primates alone. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

On the psychological origins of tool use.

The ubiquity of tool use in human life has generated multiple lines of scientific and philosophical investigation to understand the development and expression of humans' engagement with tools and its relation to other dimensions of human experience. However, existing literature on tool use faces several epistemological challenges in which the same set of questions generate many different answers. At least four critical questions can be identified, which are intimately intertwined-(1) What constitutes tool use? (2) What psychological processes underlie tool use in humans and nonhuman animals? (3) Which of these psychological processes are exclusive to tool use? (4) Which psychological processes involved in tool use are exclusive to Homo sapiens? To help advance a multidisciplinary scientific understanding of tool use, six author groups representing different academic disciplines (e.g., anthropology, psychology, neuroscience) and different theoretical perspectives respond to each of these questions, and then point to the direction of future work on tool use. We find that while there are marked differences among the responses of the respective author groups to each question, there is a surprising degree of agreement about many essential concepts and questions. We believe that this interdisciplinary and intertheoretical discussion will foster a more comprehensive understanding of tool use than any one of these perspectives (or any one of these author groups) would (or could) on their own.

End the search quickly: Pigeons (Columba livia) and humans (Homo sapiens) share the same bias.

Comments on an article by W. T. Herbranson et al. (see record 2022-07304-001). The article by Herbranson et al. illustrates the care that must be taken, both in designing comparative research and in interpreting the findings, to understand how specific features of experimental design impact each species' choices. Herbranson et al. presented to pigeons a decision-making challenge known informally as "The Secretary Problem", a problem cast in the form of selecting a candidate for a job. The task is to make a single choice among a finite set of options when these options are presented in succession. The chooser must select a given option or pass on to the next without knowing what the remaining options are. Decisions are final-one either rejects an option when it appears or selects that option, ending the search. The authors trained pigeons to recognize the "reward value" of five different colors on keys that they could peck. Herbranson et al. subsequently replicated the study with humans, presenting humans with probabilistic outcomes (rather than the certain outcomes of varying value presented in earlier studies with humans). Their aim was to explore the consequences of altering reinforcement options on humans' choices, so as to understand more fully the ways in which pigeons and humans approach this problem. Herbranson et al.'s work is an example of the power of carefully constructed comparative behavioral experiments to expand the understanding of ourselves and other species in unexpected ways. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

African striped mice (Rhabdomys) mind the neighbors.

This feature essay discusses the African striped mice (Rhabdomys) and how closely related-species differ in behavior based on their environment. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

How tufted capuchin monkeys (Sapajus spp.) and humans (Homo sapiens) handle a jointed tool.

The embodied theory of tooling predicts that when using a grasped object as a tool, individuals accommodate their actions to manage the altered degrees of freedom in the body-plus-object system. We tested predictions from this theory by studying how 3 tufted capuchin monkeys (Sapajus spp.) and 6 humans (Homo sapiens) used a hoe to retrieve a token. The hoe's handle was rigid, had 2 segments with 1 planar joint, or had 3 segments with 2 (orthogonal) planar joints. When jointed, rotating the handle could render it rigid. The monkeys used more actions to retrieve the token when the handle had 1 joint than when it had no joints or 2 joints. They did not use exploratory actions frequently nor in a directed manner in any condition. Although they sometimes rotated the handle of the hoe, they did not make it rigid. In a follow-up study, we explored whether humans would rotate the handle to use a 2-jointed hoe in a conventional manner, as predicted both by the embodied theory and theories of functional fixedness in humans. Two people rotated the handle to use the hoe conventionally, but 4 people did not; instead, they used the hoe as it was presented, as did the monkeys. These results confirm some predictions but also highlight shortcomings of the embodied theory with respect to specifying the consequences of adding multiple degrees of freedom. The study of species' perceptual sensitivity to jointed object's inertial properties could help to refine the embodied theory of tooling. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

One hundred years of the Journal of Comparative Psychology.

The year 2021 marks the 100th year of publication of the Journal of Comparative Psychology by the American Psychological Association. To mark the centennial of the Journal of Comparative Psychology, a series of essays by diverse authors will appear in the four issues of Volume 135. Some of them concern the history of the journal, key figures in its history, and of the discipline; others concern the discipline's current status and its likely near future (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Comparative psychology's founding mother, Margaret Floy Washburn.

A scientific discipline grows through the insights and labors of individual scientists, honed by their discussions among colleagues and the mentoring they provide to the next generation of scientists. Margaret Floy Washburn, president of the American Psychological Association in 1921, the founding year of the Journal of Comparative Psychology, was a large presence during the early years of comparative psychology. She was a consummate scientist in all the abovementioned dimensions: insights, labors, communicating with her peers (including, a century later, readers of her voluminous writings), and mentoring. This essay provides an overview of her professional life and, more importantly, a synopsis of her major theoretical work, Movement and Mental Imagery, published in 1916. Her theoretical insights are remarkably relevant to contemporary developments in comparative psychology and related subdisciplines in psychology. She is an admirable founding mother for the discipline. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

A new look at universals and specificities in the songs of humpback whales.

In this issue's featured article, Mercado and Perazio (2021) describe songs of humpback whales using acoustic qualities, in part to determine the degree of similarity in songs across time and space that have not been revealed by information-theoretic analyses. They are particularly interested in evaluating alternative explanations of song variations in humpback whales. They argue that if humpback whales' songs "are . . . transmitted through acoustic contact followed by imitation" (p. 29) then (a) songs of populations not in acoustic contact should diverge, (b) songs of the same population should diverge increasingly over time, and (c) song forms separated by multiple decades either within or across populations should be dissimilar. Alternatively, acoustic similarities in song structure across populations and/or across decades in the same population would challenge the hypothesis that socially mediated learning is the primary driver of variation in the structure of humpback whales' songs over time. If that is the case, then identifying universal properties of song composition is important to move the field forward. Broadening the analytical tool kit can help in this effort. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Anticipating future actions: Motor planning improves with age in wild bearded capuchin monkeys (Sapajus libidinosus).

Self-directed object manipulation tasks illuminate development of motor planning. Grasping strategies that lead to good object control to perform the following action(s) reveal second-order motor planning. Motor planning for efficient grips develops slowly in children. Age-related differences in other primates have been poorly investigated. Here, we investigated anticipatory motor planning of infant, juvenile and adult wild capuchin monkeys grasping a horizontally positioned stick baited to the left or right side (a version of the elevated spoon task). We recorded the grasps capuchins used to bring the baited end of the stick to the mouth. The percentage of efficient radial grips positively correlated with age and adults used efficient grips significantly more frequently than infants. Adult wild capuchins' use of radial grips was higher than that reported for adult captive capuchins in similar tasks, suggesting that experience throughout life may influence motor anticipation. Self-directed object manipulation tasks will be useful to compare this aspect of cognition across primates. A video abstract of this article can be viewed at https://youtu.be/a1Zbr_AQkb8.

Revisiting the fourth dimension of tool use: how objects become tools for capuchin monkeys.

Culture allows humans to adapt to a diversity of contexts. Participatory experience in technical activities and activity with artefacts provide the basis for learning traditional technical skills. Some populations of non-human animals use tools. The ways in which artefacts influence the development of a traditional skill in non-human species can provide insight into essential supports for technical traditions in humans and shared learning processes across species. In wild bearded capuchins, nut cracking leaves edible pieces of nuts, nut shells and stones used as hammers at anvil sites. We addressed how mastery of cracking nuts by young monkeys is associated with interactions with these objects. We studied monkeys' reuse of nuts, hammers and anvils and the outcome of attempts to crack nuts, and from these data derived their behavioural variability and proficiency in nut cracking. Behavioural variability was the most robust predictor of whether a monkey collects pieces of nuts cracked by others or reuses stones and nuts, and was a stronger predictor of proficiency than age. Young monkeys were increasingly likely to reuse the stone used by another after the other monkey had left the anvil as they increasingly focused their behaviour on actions relevant to cracking nuts.

Optional tool use: The case of wild bearded capuchins (Sapajus libidinosus) cracking cashew nuts by biting or by using percussors.

Tool use in humans can be optional, that is, the same person can use different tools or no tool to achieve a given goal. Strategies to reach the same goal may differ across individuals and cultures and at the intra-individual level. This is the first experimental study at the intra-individual level on the optional use of a tool in wild nonhuman primates. We investigated optional tool use by wild bearded capuchins (Sapajus libidinosus) of Fazenda Boa Vista (FBV; Piauí, Brazil). These monkeys habitually succeed in cracking open the mesocarp of dry cashew nuts (Anacardium spp.) by pounding them with stones and/or by biting. We assessed whether availability of a stone and resistance of the nut affected capuchins' choice to pound or to bite the nuts and their rates of success. Sixteen capuchins (1-16 years) received small and large dry cashew nuts by an anvil together with a stone (Stone condition) or without a stone (No-Stone condition). In the Stone conditions, subjects used it to crack the nut in 89.1% (large nuts) and 90.1% (small nut) of the trials. Nut size significantly affected the number of strikes used to open it. Availability of the stone significantly increased the average percent of success. In the No-Stone conditions, monkeys searched for and used other percussors to crack the nuts in 54% of trials. In all conditions, age affects percentage of success and number of strikes to reach success. We argue that exclusive use of stones in other sites may be due to the higher abundance of stones at these sites compared with FBV. Since capuchins opened cashews with a tool 1-2 years earlier than they succeed at cracking more resistant palm nuts, we suggest that success at opening cashew nuts with percussors may support the monkeys' persistent efforts to crack palm nuts.

Dexterity and technique in termite fishing by chimpanzees (Pan troglodytes troglodytes) in the Goualougo Triangle, Republic of Congo.

Although the phenomenon of termite fishing by chimpanzees (Pan troglodytes) has historical and theoretical importance for primatology, we still have a limited understanding of how chimpanzees accomplish this activity, and in particular, about details of skilled actions and the nature of individual variation in fishing techniques. We examined movements, hand positions, grips, and other details from remote video footage of seven adult and subadult female chimpanzees using plant probes to extract Macrotermes muelleri termites from epigeal nests. Six chimpanzees used exclusively one hand (left or right) to grip the probe during termite fishing. All chimpanzees used the same repertoire of actions to insert, adjust, and withdraw the probe but differed in the frequency of use of particular actions. Chimpanzees have been described as eating termites in two ways-directly from the probe or by sweeping them from the probe with one hand. We describe a third technique: sliding the probe between the digits of one stationary hand as the probe is extracted from the nest. The sliding technique requires complementary bimanual coordination (extracting with one hand and grasping lightly with the other, at the same time). We highlight the importance of actions with two hands-one gripping, one assisting-in termite fishing and discuss how probing techniques are correlated with performance. Additional research on digital function and on environmental, organismic, and task constraints will further reveal manual dexterity in termite fishing.

Ingestive behaviors in bearded capuchins (Sapajus libidinosus).

The biomechanical and adaptive significance of variation in craniodental and mandibular morphology in fossil hominins is not always clear, at least in part because of a poor understanding of how different feeding behaviors impact feeding system design (form-function relationships). While laboratory studies suggest that ingestive behaviors produce variable loading, stress, and strain regimes in the cranium and mandible, understanding the relative importance of these behaviors for feeding system design requires data on their use in wild populations. Here we assess the frequencies and durations of manual, ingestive, and masticatory behaviors from more than 1400 observations of feeding behaviors video-recorded in a wild population of bearded capuchins (Sapajus libidinosus) at Fazenda Boa Vista in Piauí, Brazil. Our results suggest that ingestive behaviors in wild Sapajus libidinosus were used for a range of food material properties and typically performed using the anterior dentition. Coupled with previous laboratory work indicating that ingestive behaviors are associated with higher mandibular strain magnitudes than mastication, these results suggest that ingestive behaviors may play an important role in craniodental and mandibular design in capuchins and may be reflected in robust adaptations in fossil hominins.

Odds favor the bees.

Muszynski and Couvillon (see record 2020-37265-001) built upon their previous findings that honeybees can learn the relation among triads of trial-unique visual stimuli. In this new work, they showed that bees encountering trial-unique sets of three or four visual stimuli chose the correct stimulus at above-chance levels, replicating their previous findings and extending them to four-choice displays. In the first experiment, the bees' performance with triads of stimuli was unaffected by whether the correct choice was patterned or solid, or whether the stimuli shared a common color. A control group in this experiment encountered a categorical discrimination problem with two stimuli. This latter group of bees easily learned the discrimination and made a lower proportion of errors than bees solving the oddity problem, suggesting that the bees did not perceive the oddity task as a discrimination problem. The possibility that bees solved the oddity problem as a categorical discrimination was further examined in a second experiment. In that experiment, one group of bees encountered quartets of disks in combinations of solid color and two-color disks, and another group encountered only two-color disks. The authors expected that the addition of an irrelevant category (solid or two-color disk) would make the odd stimulus more discriminable, and, therefore, improve performance in that group compared with the group that encountered only two-colored disks. Their expectation was confirmed: Bees that encountered stimuli with a categorical difference, even though the category was irrelevant to which disk (of four) was odd, averaged more correct choices (average .67 vs. .47 across 15 trials; .25 expected by chance) and reached a higher terminal level of performance than bees that encountered only two-color disks (nearing .90 vs. around .50 correct, Trials 14 -16, solid and pattern group vs. pattern-only group, respectively). (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Isotopic and elemental corroborates for wild bearded capuchin (Sapajus libidinosus) omnivorous dietary adaptation at Fazenda Boa Vista, Brazil.

RATIONALE: This study analyzes variability in the diets of wild bearded capuchin monkeys, Sapajus libidinosus, by analyzing stable carbon (δ13 C) and nitrogen (δ15 N) isotope ratios and elemental concentrations (%C and %N) of fecal samples and food items. Developing isotopic and elemental correlates for diets of habituated subjects is a necessary step towards applying similar methods to interpret diets of unhabituated or cryptic subjects. METHODS: Fecal samples from wild capuchins and their foods were collected at Fazenda Boa Vista, Brazil. Fecal samples from laboratory-housed Sapajus spp. and their foods were analyzed to establish diet-feces offsets for δ13 C, δ15 N, %C, and %N. Samples were dried, powdered, and measured for isotopic and elemental values. A Bayesian mixing model commutes isotopic and elemental data from wild capuchins into likely proportions of different food categories. RESULTS: The captive study shows small diet-feces spaces for Sapajus spp. of -0.8 ± 0.7‰ for δ13 C, -0.2 ± 0.4‰ for δ15 N, -6.1 ± 1.7% for %C, and -1.0 ± 0.6% for %N. The wild study shows omnivorous diets based on C3 , C4 , and CAM plants, and fauna. Subject diets are highly varied within and between days. Fecal data show age-related differences in diet and crop-raiding. There is no consistent isotopic or elemental difference between mothers and infants. CONCLUSIONS: Fecal stable isotope and elemental evidence employed in a Bayesian mixing model reflects the highly varied diets of capuchin monkeys in an isotopically heterogeneous environment. The isotopic and elemental variability reported here will aid similar diet reconstructions among unhabituated subjects in the future, but precludes tracking weaning isotopically among capuchins in this environment.

Adult and juvenile bearded capuchin monkeys handle stone hammers differently during nut-cracking.

Wild bearded capuchin monkeys (Sapajus libidinosus) habitually use stone hammers to crack open palm nuts and seeds on anvils. This activity requires strength, balance, and precise movement of a large stone with respect to the item placed on an anvil. We explored how well young monkeys cope with these challenges by examining their behavior and the behavior of adults while they cracked palm nuts using a stone. Using video records, we compared actions of six juvenile (2-5 years) and six adult (7+ years) wild monkeys during their first 20 strikes with one unfamiliar ellipsoid, quartzite stone (540 g), and the outcomes of these strikes. Compared with adults, juveniles cracked fewer nuts, performed a more diverse set of exploratory actions, and less frequently placed one or both hands on top of the stone on the downward motion. Adults and juveniles displayed similar low frequencies of striking with a slanted trajectory, missing the nut, and losing control over the nut or stone after striking. These findings indicate that young monkeys control the trajectory of a stone adequately but that is not sufficient to crack nuts as effectively as adults do. Compared with juveniles, adults more quickly perceive how to grip the stone efficiently, and they are able to adjust their grip dynamically during the strike. Young monkeys develop expertise in the latter aspects of cracking nuts over the course of several years of regular practice, indicating that perceptual learning about these aspects of percussion occurs slowly. Juvenile and adult humans learning to use stones to crack nuts also master these features of cracking nuts very slowly.

Compound grips in tufted capuchin monkeys (Sapajus spp and Sapajus libidinosus).

An experimental study with captive individuals and study of video recordings of wild monkeys explored whether and how tufted capuchin monkeys use onehand to hold one or more objects with multiple grips (compound grips). A task designed to elicit compound grip was presented to five captive tufted capuchin monkeys (Sapajus spp). The monkeys held one to four balls in onehand and dropped the balls individually into a vertical tube. Multiple simple grips and independent digit movements enabled separate control of multiple objects in one hand. Monkeys always supported the wrist on the horizontal edge of the tube before releasing the ball. Increasing the number of balls decreased the likelihood that the monkeys managed the task. Wild bearded capuchins (Sapajus libidinosus) used compound grips spontaneously to store multiple food items. Compound grips have been described in macaques, gorillas, chimpanzees, and humans, and now in a New World primate. We predict that any primate species that exhibits precision grips and independent digit movement can perform compound grips. Our findings suggest many aspects of compound grip that await investigation.