Chimpanzees (Pan troglodytes) in U.S. Zoos, Sanctuaries, and Research Facilities: A Survey-Based Comparison of Species-Typical Behaviors

A survey was sent to zoos, research facilities, and sanctuaries which housed chimpanzees. Data collected included information about 1122 chimpanzees’ age, sex, social group-size, rearing history, and enclosure. Respondents were also asked to indicate if certain behaviors had been observed in each chimpanzee over the prior two years. Species- typical behaviors (STBs) were queried, including copulation, tool-use, nest-building, and social grooming. Tool-use was reported present for 94.3% of the sample (n = 982), active social grooming for 85.7% (n = 1121), copulation for 68.3% (n = 863) and nest-building for 58.9% (n = 982). Of the subjects for whom we had data regarding all four STBs (n = 860), 45.6% were reported to engage in all four. Logistic regression analyses using forward Wald criteria were conducted to determine the best model for each STB based on the predictors of age, sex, rearing history, group-size, facility-type, and a sex-by-rearing interaction. The best model for copulation (χ2(6) = 124.62, p < 0.001) included rearing, group-size, facility-type, and the sex-by-rearing interaction. Chimpanzees were more likely to copulate if they were mother-reared, in larger groups, living in research facilities, and, if not mother-reared (NOTMR), more likely to copulate if they were female. The best model for tool-use retained the predictors of age category, facility-type, and sex-by-rearing (χ2(5) = 55.78, p < 0.001). Chimpanzees were more likely to use tools if they were adult, living in research facilities, and if NOTMR, were female. The best model for nest-building included facility-type and rearing (χ2(3) = 205.71, p < 0.001). Chimpanzees were more likely to build nests if they were MR and if they were living in zoos or in sanctuaries. The best model for active social grooming retained the predictors of age, sex, rearing, and type of facility (χ2(6) = 102.15, p < 0.001). Chimpanzees were more likely to engage in active social grooming if they were immature, female, mother-reared, and living in zoos. This research provides a basic behavioral profile for many chimpanzees living under human care in the United States and allows us to determine potential methods for improving the welfare of these and future chimpanzees in this population.

Familiarity mediates apes' attentional biases toward human faces

In zoos, primates experience markedly different interactions with familiar humans, such as the zookeepers who care for them, compared with those with unfamiliar humans, such as the large volume of zoo visitors to whom they are regularly exposed. While the behaviour of zoo-housed primates in the presence of unfamiliar, and to a lesser extent familiar, humans has received considerable attention, if and how they spontaneously distinguish familiar from unfamiliar people, and the cognitive mechanisms underlying the relationships they form with familiar and unfamiliar humans, remain poorly understood. Using a dot-probe paradigm, we assessed whether primates (chimpanzees and gorillas) show an attentional bias toward the faces of familiar humans, with whom the apes presumably had a positive relationship. Contrary to our predictions, all subjects showed a significant attentional bias toward unfamiliar people's faces compared with familiar people's faces when the faces showed a neutral expression, both with and without a surgical face mask on, but no significant attentional bias when the faces showed a surprised expression. These results demonstrate that apes can spontaneously categorize humans based on familiarity and we argue that the attentional biases the apes showed for unfamiliar human faces reflect a novelty effect.

Younger generations are more interested than older generations in having non-domesticated animals as pets

The trade and private ownership of non-domesticated animals has detrimental effects on individual animals and their wild populations. Therefore, there is a need to understand the conditions that motivate and dissuade interest in non-domesticated pet ownership. Past research has demonstrated that the way in which non-domesticated animals are portrayed in images influences the public’s perception that they are suitable as pets. We conducted an online survey of people residing in the United States to investigate how viewing images that could be realistically captured in the zoo and broader tourism industries impact the degree to which people report interest in having that animal as a pet. We focused on two species, reticulated pythons (Malayopython reticulatus) and two-toed sloths (Choloepus hoffmanni), and presented each species in six different visual contexts. After viewing an image, respondents reported interest in pet ownership on a four-point Likert scale. Each species was studied separately in a between-subjects design and results were analyzed using ordinal logistic regression models. Thirty-nine percent of respondents reported interest in sloth pet ownership, and 21% reported interest in python pet ownership. However, contrary to our hypotheses, we found that viewing these species in different visual contexts did not significantly affect survey respondents’ reported interest in having either species as a pet. Generation was a significant predictor of interest in both sloth and python pet ownership, with younger generations reporting more interest in having these species as pets. Male respondents reported more interest in python pet ownership, whereas there were no significant differences between genders regarding interest in sloth ownership. We consider how modern media exposure to animals in unnatural contexts may relate to the generational effect and discuss priorities for future research to better understand the development of individual interests in non-domesticated pet ownership.

The relationship between personality, season, and wounding receipt in zoo-housed Japanese macaques (Macaca fuscata): A multi-institutional study

It is important to those managing Japanese macaques (Macaca fuscata) in captive settings to understand predictors of wounding. While studies have demonstrated that season (breeding or nonbreeding) and sex predict rates of wounding received by zoo-housed Japanese macaques, we investigated whether individual differences in personality ratings also might explain some of the observed interindividual variance in wounding. Such patterns were previously observed in rhesus macaques (M. mulatta), such that individuals rated higher on Anxiety and Confidence received greater wounding. Here, we collected wounding data over 24 months on 48 Japanese macaques from eight AZA-accredited zoos. Each macaque was also rated by keepers using a 26-item personality questionnaire. Principle components analysis of these ratings revealed four personality components: Openness, Friendliness, Dominance, and Anxiety/Reactivity. The model with the best fit revealed an interaction effect between season (breeding vs. nonbreeding) and the personality component Friendliness, such that individuals rated higher on Friendliness incurred fewer wounds in the nonbreeding season. The second-best model revealed both a main effect of the season as well as an interaction effect between season and Openness, such that macaques rated higher in Openness received more wounds in the nonbreeding season than those rated lower in Openness. Thus, as with rhesus macaques, personality mediated wounding receipt rate in Japanese macaques, although different personality components explained interindividual variance in wounding for these two species. These differences likely reflect species differences in behavior and personality structure, as well as the influence of differing management practices, highlighting the importance of species-specific approaches for captive primate care and welfare. This study provides further support for understanding primate personality to create individualized strategies for their care.

An evaluation of thermal imaging as a welfare monitoring tool for captive chimpanzees

Among the growing list of novel tools with which to assess animal welfare is the use of thermal (infrared) imaging. The technology has already been utilized to identify emotional arousal in several nonhuman primate species, though most of these approaches have necessitated the use of relatively controlled settings. Here, we were interested to determine the feasibility of such techniques in a sanctuary setting in which chimpanzees were unrestrained and able to move freely around their enclosures. Furthermore, we sought to evaluate how such thermal images could be paired with corresponding long-term behavioral data and contribute to a multifactorial welfare monitoring system. Over a 6-month period, we simultaneously collected both behavioral and thermographic data on 29 chimpanzees living in four social groups. While we took a thermal image with every behavioral data point, we found that only a small proportion (6.38%) of the thermal images we captured were of sufficient quality to analyze. Most of these usable thermal images (55%) corresponded with a behavioral observation scored as "inactive," and thus other, less frequent behaviors are not so well represented in our final data set. From our data set, we were able to determine that nasal temperatures were relatively lower when chimpanzees were categorized in active behaviors compared to inactive behaviors, providing some validity measures to our approach. While there are other potential applications for thermal imaging in the behavioral management of chimpanzees, managers should consider the practical limitations of developing long-term welfare monitoring programs that rely on thermographic data.

Comparative survival analyses among captive chimpanzees (Pan troglodytes) in America and Japan

Detailed, long-term datasets on the life histories of long-lived species such as great apes are necessary to understand their survival patterns but are relatively rare. Such information requires prolonged and consistent record-keeping over many generations, so for chimpanzees (Pan troglodytes), this equates to many decades of input. As life history variables can be altered by differences in environmental influences (whether natural or artificial), there is substantial value to being able to compare across populations. Here, we present the first comparative analysis of life history data for two ex situ chimpanzee populations residing in North America (1975–2020; n = 730) and Japan (1980–2020; n = 660). Overall, survival patterns were similar between regions, and the median life expectancy from birth is estimated at 35.7 (95% CI = [32.4–40.0]) years for females and 30.1 (27.3–34.3) years for males across both populations. Females who survive to their first birthday are estimated to survive 42.4 (40.0–46.3) years and males 35.5 (32.6–38.0) years. We found that birth type (wild-born or captive-born) did not influence survival patterns in either population, but there were differential effects of sex on longevity. In the America population, males had higher mortality rates than females, whereas in the Japan population we found no differences between the sexes. First year mortality did not differ between populations for males (18–20%), but for females it was lower in America (15%) compared to Japan (25%). Survival patterns of chimpanzees in the present study will be useful for future investigation into potential causes of regional differences and cross-species comparisons.

Evolution of water conservation in humans

To sustain life, humans and other terrestrial animals must maintain a tight balance of water gain and water loss each day.^1-3 However, the evolution of human water balance physiology is poorly understood due to the absence of comparative measures from other hominoids. While humans drink daily to maintain water balance, rainforest-living great apes typically obtain adequate water from their food and can go days or weeks without drinking^4-6. Here, we compare isotope-depletion measures of water turnover (L/d) in zoo- and rainforest-sanctuary-housed apes (chimpanzees, bonobos, gorillas, and orangutans) with 5 diverse human populations, including a hunter-gatherer community in a semi-arid savannah. Across the entire sample, water turnover was strongly related to total energy expenditure (TEE, kcal/d), physical activity, climate (ambient temperature and humidity), and fat free mass. In analyses controlling for those factors, water turnover was 30% to 50% lower in humans than in other apes despite humans' greater sweating capacity. Water turnover in zoo and sanctuary apes was similar to estimated turnover in wild populations, as was the ratio of water intake to dietary energy intake (∼2.8 mL/kcal). However, zoo and sanctuary apes ingested a greater ratio of water to dry matter of food, which might contribute to digestive problems in captivity. Compared to apes, humans appear to target a lower ratio of water/energy intake (∼1.5 mL/kcal). Water stress due to changes in climate, diet, and behavior apparently led to previously unknown water conservation adaptations in hominin physiology.

A Comparative Perspective on Three Primate Species' Responses to a Pictorial Emotional Stroop Task

The Stroop effect describes interference in cognitive processing due to competing cognitive demands. Presenting emotionally laden stimuli creates similar Stroop-like effects that result from participants' attention being drawn to distractor stimuli. Here, we adapted the methods of a pictorial Stroop study for use with chimpanzees (N = 6), gorillas (N = 7), and Japanese macaques (N = 6). We tested all subjects via touchscreens following the same protocol. Ten of the 19 subjects passed pre-test training. Subjects who reached criterion were then tested on a standard color-interference Stroop test, which revealed differential accuracy in the primates' responses across conditions. Next, to test for an emotional Stroop effect, we presented subjects with photographs that were either positively valenced (a preferred food) or negatively valenced (snakes). In the emotional Stroop task, as predicted, the primates were less accurate in trials which presented emotionally laden stimuli as compared to control trials, but there were differences in the apes' and monkeys' response patterns. Furthermore, for both Stroop tests, while we found that subjects' accuracy rates were reduced by test stimuli, in contrast to previous research, we found no difference across trial types in the subjects' response latencies across conditions.

Primates' Food Preferences Predict Their Food Choices Even Under Uncertain Conditions

Primates’ food preferences are typically assessed under conditions of certainty. To increase ecological validity, and to explore primates’ decision making from a comparative perspective, we tested three primate species (Pan troglodytes, Gorilla gorilla gorilla, Macaca fuscata) (N = 18) in two food-preference tests that created different conditions of uncertainty. In the first, we showed subjects pairs of photographs of six foods in a randomized manner within each session, so subjects could not predict the next pairing and had to respond in accordance with their preferences. We found individual differences in subjects’ preference and differences in six subjects’ preferences when comparing their selections in this test to selections made when trials were blocked by food pairing (tested previously: Huskisson et al., 2020). In in each trial of the second test we paired the food stimuli with a ‘chance’ symbol, representing a random reward of one of the six foods. Across species, each subject’s propensity to select chance over the known food varied by food type: when the known option was highly preferred, subjects were less likely to select the chance symbol. Additionally, 61.11% of the subjects’ rates of selecting foods in the first test showed a positive trend with the rates of selecting the same foods under conditions of uncertainty here; three of these subjects’ selection rates were significantly correlated between tests. Finally, if the food chimpanzees received for selecting the chance symbol was a preferred food, they were more likely to select chance again in the subsequent trial.

Do zoo visitors induce attentional bias effects in primates completing cognitive tasks?

While previous research has focused on the impact of visitors on zoo-housed animals' behavior, here, we evaluated the impact of visitors on the performance of four zoo-housed Japanese macaques (Macaca fuscata) in a cognitive task. The macaques completed a touchscreen-based match-to-sample task in glass-sided booths at the perimeter of their enclosure, adjacent to a visitor viewing area. The task was novel to all macaques at the start of this study but over the 6-month testing period the macaques showed increased accuracy on the task, suggestive of learning. We recorded the number of visitors within the viewing area roughly every 12 trials each macaque completed. We categorized visitor counts as small (0-20), medium (21-40), and large (41-60) crowds and we considered the macaques' response latencies and accuracy by crowd size and study period (first 3 months versus second 3 months). If visitor presence negatively influenced performance, we predicted that macaques' accuracy would decrease but response times would increase with crowd size. We found effects of crowd size and study period on the macaques' accuracy. In the first period, the macaques performed at chance and accuracy did not differ across crowd categories. In the second period, the macaques' accuracy improved as compared to the first period, but their accuracy was mediated by crowd size: the macaques were significantly more accurate in the presence of small crowds than medium or large crowds. The macaques' response latencies also varied by study period and crowd size, but we found no evidence of a response-slowing effect.

A review of research in primate sanctuaries

While non-human primate studies have long been conducted in laboratories, and more recently at zoological parks, sanctuaries are increasingly considered a viable setting for research. Accredited sanctuaries in non-range countries house thousands of primates formerly used as subjects of medical research, trained performers or personal pets. In range countries, however, sanctuaries typically house orphaned primates confiscated from illegal poaching and the bushmeat and pet trafficking trades. Although the primary mission of these sanctuaries is to rescue and rehabilitate residents, many of these organizations are increasingly willing to participate in non-invasive research. Notably, from a scientific standpoint, most sanctuaries provide potential advantages over traditional settings, such as large, naturalistic physical and social environments which may result in more relevant models of primates' free-ranging wild counterparts than other captive settings. As a result, an impressive scope of research in the fields of primate behaviour, cognition, veterinary science, genetics and physiology have been studied in sanctuaries. In this review, we examine the range and form of research that has been conducted at accredited sanctuaries around the world. We also describe the potential challenges of sanctuary-based work and the considerations that external researchers may face when deciding to collaborate with primate sanctuaries on their research projects.

Food Cleaning by Japanese Macaques: Innate, Innovative or Cultural?

Japanese macaques (Macaca fuscata) display a number of cultural behaviours including food washing, stone handling and certain grooming techniques. These are deemed cultural behaviours because it is presumed that they are socially learned and, importantly, that social learning is essential for their emergence. Recently, however, research has revealed that culturally naïve primates can re-innovate presumed cultural behaviours. These behaviours are said to fall within that species' "zone of latent solutions" (ZLS). A notable cultural behaviour of Japanese macaques is food washing, first reported by Japanese researchers studying wild Japanese macaques in the 1950s. To test whether culturally naïve Japanese macaques would spontaneously wash food and also, therefore, whether food-washing behaviour is within their ZLS, we presented 12 zoo-housed macaques with sweet potato covered in sand near a pool in their exhibit. Over 11 days we recorded the macaques' behaviour. While 11 of the 12 macaques ate the potato pieces, none washed them. However, 4 macaques cleaned their food, brushing off the sand using their hand or rubbing the potato against their body or another food item, using three distinct techniques. We found no change over time in the rate at which monkeys cleaned or consumed potato, but there was a significant positive correlation between the number of potato pieces a monkey ate and the number of cleaning behaviours performed. We conclude that, minimally, food-cleaning behaviour is within macaques' ZLS.

Sex and season predict wounds in zoo-housed Japanese macaques (Macaca fuscata): A multi-institutional study

Japanese macaque societies are characterized by frequent intragroup conflict both in free-ranging and zoo-housed conditions. In zoos, understanding the factors that contribute to wounding is of interest because this knowledge can aid in proactive husbandry and management planning that can minimize the negative impacts wounding can have on individual welfare. This study sought to determine whether the variables sex, season and age predicted wounding rates. Data were collected for 24 months on 119 Japanese macaques living in 10 zoos, and we analyzed the contribution of variables using generalized linear mixed models. A total of 1,007 wounds were reported, and the best model included the interaction between sex and season. Follow-up analyses revealed that females incurred more wounds than males, and this sex difference was more pronounced during the breeding compared to the nonbreeding season. On average, individuals received 4.67 (±SEM: 0.55) wounds per year and 77.31% of the population incurred at least one wound in the study period. The majority of wounds were superficial and did not require veterinary intervention. Wound locations were not randomly distributed across body regions and were most often reported on the face. Finally, macaques living in larger social groups experienced more wounds, on average. This study represents the first quantification of wounding in this species and may provide insight to help inform husbandry and management strategies in zoos.

Reducing the primate pet trade: Actions for primatologists

This commentary emerged from a panel presentation at the International Primatological Society Congress in Nairobi, Kenya, 2018. The goal was to provide regional updates on the status of primate removal from habitat countries, especially for the pet trade, and develop guidelines that could help primatologists address this critical problem. The trade in live primates includes those used as pets, in entertainment, and as subjects of biomedical experimentation, but here we focus on those primates destined for the pet trade. Such transactions are a hugely lucrative business, impacting hundreds of thousands of individuals annually and affecting the survival of wild populations. Being intimately familiar with primate social behavior, life history and biology, primatologists, whether they work with captive or wild primates, are in a unique position to understand the nature of the trade and attempt to counter its effects. In addition to updating the status of the primate pet trade, we provide recommendations that may help primatologists formulate a plan to deal, locally and regionally, with illegal trafficking in live primates. General guidelines include increasing awareness of local customs, policies and laws; developing collaborative research opportunities for local people; engaging in training/informational opportunities; and instructing on how to take action when encountering illegally-trafficked primates.

The effect of captivity on the primate gut microbiome varies with host dietary niche

Despite careful attention to animal nutrition and wellbeing, gastrointestinal distress remains relatively common in captive non-human primates (NHPs), particularly dietary specialists such as folivores. These patterns may be a result of marked dietary differences between captive and wild settings and associated impacts on the gut microbiome. However, given that most existing studies target NHP dietary specialists, it is unclear if captive environments have distinct impacts on the gut microbiome of NHPs with different dietary niches. To begin to examine this question, we used 16S ribosomal RNA gene amplicon sequences to compare the gut microbiomes of five NHP genera categorized either as folivores (Alouatta, Colobus) or non-folivores (Cercopithecus, Gorilla, Pan) sampled both in captivity and in the wild. Though captivity affected the gut microbiomes of all NHPs in this study, the effects were largest in folivorous NHPs. Shifts in gut microbial diversity and in the relative abundances of fiber-degrading microbial taxa suggest that these findings are driven by marked dietary shifts for folivorous NHPs in captive settings. We propose that zoos and other captive care institutions consider including more natural browse in folivorous NHP diets and regularly bank fecal samples to further explore the relationship between NHP diet, the gut microbiome, and health outcomes.

Establishing an infrastructure for collaboration in primate cognition research

Inferring the evolutionary history of cognitive abilities requires large and diverse samples. However, such samples are often beyond the reach of individual researchers or institutions, and studies are often limited to small numbers of species. Consequently, methodological and site-specific-differences across studies can limit comparisons between species. Here we introduce the ManyPrimates project, which addresses these challenges by providing a large-scale collaborative framework for comparative studies in primate cognition. To demonstrate the viability of the project we conducted a case study of short-term memory. In this initial study, we were able to include 176 individuals from 12 primate species housed at 11 sites across Africa, Asia, North America and Europe. All subjects were tested in a delayed-response task using consistent methodology across sites. Individuals could access food rewards by remembering the position of the hidden reward after a 0, 15, or 30-second delay. Overall, individuals performed better with shorter delays, as predicted by previous studies. Phylogenetic analysis revealed a strong phylogenetic signal for short-term memory. Although, with only 12 species, the validity of this analysis is limited, our initial results demonstrate the feasibility of a large, collaborative open-science project. We present the ManyPrimates project as an exciting opportunity to address open questions in primate cognition and behaviour with large, diverse datasets.

Systemic response of coated-platelet and peripheral blood inflammatory cell indices after aneurysmal subarachnoid hemorrhage and long-term clinical outcome

PURPOSE

Post-hemorrhage period after aneurysmal subarachnoid hemorrhage (aSAH) has several systemic manifestations including prothrombotic and pro-inflammatory states. Inter-relationship between these states using established/routine laboratory biomarkers and its long-term effect on clinical outcome is not well-defined.

MATERIALS AND METHODS

Retrospective analysis of prospective cohort of 44 aSAH patients. Trend of procoagulant biomarkers [coated-platelets, mean platelet volume to platelet count (MPV:PLT)] and peripheral inflammatory biomarkers [platelet-lymphocyte ratio (PLR), neutrophil-platelet ratio (NLR)] were analyzed using regression analysis. Occurrence of delayed cerebral ischemia (DCI), modified Rankin score (mRS) of 3-6 and Montreal cognitive assessment (MoCA) of <26 at 1-year defined adverse clinical outcome.

RESULTS

Patients with worse mRS and MoCA score had higher rise in coated-platelet compared to those with better scores [20.4 (IQR: 15.6, 32.9) vs. 10.95 (IQR: 6.1, 18.9), p = 0.003] and [16.9 (IQR: 13.4, 28.1) vs. 10.95 (IQR: 6.35, 18.65), p = 0.02] respectively. NLR and PLR trends showed significant initial decline followed by a gradual rise in NLR among those without DCI as compared to persistent low levels in those developing DCI (0.13 units/day vs. -0.07 units/day, p = 0.06).

CONCLUSIONS

Coated-platelet rise after aSAH is associated with adverse long-term clinical outcome. NLR and PLR trends show an early immune-depressed state after aSAH.

Abstract WP420: Incidence of Contrast Induced Nephropathy Among Different Stroke Subtypes After Adoption of New Emergency Brain Imaging Protocol for Acute Stroke - A Single Center Perspective

Introduction: Studies demonstrating benefits of mechanical thrombectomy for large vessel occlusion (LVO) in acute ischemic stroke (AIS) has led to increased use of CT angiogram (CTA). Similarly, CTA is frequently performed to diagnose cerebrovascular pathology after intracerebral hemorrhage (ICH) and subarachnoid hemorrhage (SAH). Such contrast-enhanced CT (CECT) studies in stroke population are often associated with contrast induced nephropathy (CIN). However, incidence of CIN after adoption of increased use of CTA to diagnose LVO for possible mechanical thrombectomy is largely unknown.

Hypothesis: We investigated the incidence of CIN in acute stroke population after adoption of CECT protocol to diagnose LVO and compared it to patients undergoing CECT study for other indications.

Methods: Single-center retrospective chart review of patients presenting to the emergency room and investigated with CECT between January 2015 and December 2017. A rise in serum creatinine (SCr) 1.5 times the presenting SCr within first 72 hours of CECT defined CIN. Non-parametric Chi-squared tests were used to make intergroup comparison and a p-value of <0.05 was considered significant.

Results: Nine hundred and forty-seven charts of patients undergoing CECT were reviewed. Patients with ICH [30/132 (22.7%)] and SAH [17/126 (13.5%)] had significantly higher incidence of CIN as compared to those with AIS [11/150 (7.3%)] and non-stroke [36/494 (6.8%)] etiologies. Patients developing CIN had increased length of stay in all groups with it being statistically significant in non-stroke (p<0.0001) and ICH (p<0.004). Diabetes mellitus was identified as a significant risk factor for CIN in AIS (p=0.0094) and non-stroke population (p=0.0002). Use of antihypertensives during the first 72 hours of admission was significantly associated with CIN (p=0.0025) among non-stroke patients whereas it was not identified to be a risk factor for CIN in stroke cohort. Intravenous hydration was not associated with prevention of CIN in any of the study groups.

Conclusion: Our study results demonstrate higher incidence of CIN among patients with hemorrhagic stroke and reports risk for developing CIN in AIS is comparable to non-stroke population undergoing CECT in emergency circumstances.

A Comparison of Sequential Learning Errors Made by Apes and Monkeys Reveals Individual but not Species Differences in Learning

Using methods comparable to those used previously to test closely-related taxa (Pan troglodytes and Macaca mulatta), our aim was to better understand how gorillas (Gorilla gorilla gorilla) and Japanese macaques (M. fuscata) learn sequences. Using a disappearing-type simultaneous chain, we trained five gorillas and eight macaques on a two-item list of colored stimuli presented via touchscreens. There was no difference across species in the number of trials required to learn the two-item list. We added a third item to the list as each subject reached criterion. We then analyzed the subjects’ first 30 trials with the three-item list and found that the rate of successfully sequencing the list varied by subject but not by species. In their first 30 trials of the three-item list, subjects selected the second item correctly only at chance, suggesting they had only encoded the first symbol when learning the two-item list. One gorilla, tested on longer sequences, showed similar responses: when first presented with a newly-lengthened list, he only selected the penultimate item at chance levels. Thus, the primates’ errors with newly-lengthened lists is suggestive of the chaining theory of learning. These results highlight similarities in list learning of these two distantly-related primate species as well as the clear intra-species variation in learning.

A review of zoo-based cognitive research using touchscreen interfaces

In the past few decades, there has been an increase in the number of zoo-based touchscreen studies of animal cognition around the world. Such studies have contributed to the field of comparative cognition despite the fact research has only been performed at a relatively small number of institutions and with a narrow range of species. Nonetheless, zoo-based touchscreen studies are increasingly recognized as both having the potential to be enriching for captive animals by providing them with opportunities for choice, as well as potentially being a tool with which to measure changes in welfare. Zoo-based touchscreen research on public display also has the potential to impact zoo visitors; encouraging them not only learn more about the cognitive abilities of animals, but also potentially promoting increased respect for these species. Given the lack of a comprehensive review of this scope of specialized research, and the broad potential impacts on animals and programs, here we discuss the history, implementation, and potential outcomes of touchscreen research in zoo settings.

Personality links with lifespan in chimpanzees

Life history strategies for optimizing individual fitness fall on a spectrum between maximizing reproductive efforts and maintaining physical health over time. Strategies across this spectrum are viable and different suites of personality traits evolved to support these strategies. Using data from 538 captive chimpanzees (Pan troglodytes) we tested whether any of the dimensions of chimpanzee personality - agreeableness, conscientiousness, dominance, extraversion, neuroticism, and openness - were associated with longevity, an attribute of slow life history strategies that is especially important in primates given their relatively long lives. We found that higher agreeableness was related to longevity in males, with weaker evidence suggesting that higher openness is related to longer life in females. Our results link the literature on human and nonhuman primate survival and suggest that, for males, evolution has favored the protective effects of low aggression and high quality social bonds.

A multi-institutional assessment of a short-form personality questionnaire for use with macaques

There are two commonly-used methods for calculating primates' personality dimensions, behavioral assessments and surveys, which can be used separately or in conjunction. However, these methods have limitations. Behavioral assessments, such as the novel object test or human intruder test, often require subjects to be separated and demand highly-controlled conditions. This is likely not feasible in many zoological institutions. Furthermore, it may be difficult to replicate methods across institutions. While surveys are easier to implement, the most commonly used one - the Hominoid Personality Questionnaire (HPQ) - is long and can be time consuming to complete, especially if multiple individuals need assessing. Therefore, we developed a short-form personality questionnaire for use with macaques. We aimed to retain elements of published scales while creating a tool that would be less time consuming to complete. After creating a novel 26-item scale (28 fewer items than the HPQ), we gathered ratings for 63 Japanese macaques (Macaca fuscata) living in eight zoos accredited by the Association of Zoos and Aquariums. Using principal components analysis, we identified four components to describe the Japanese macaque personality: Openneness, Friendliness, Dominance, and Anxiety/Reactivity. While further testing is required to fully validate this scale, we tested for the convergent validity of our questionnaire by correlating the responses of a subset of the monkeys to a novel object and assessed the face validity of our scale in comparison to previously-published scales.

Radiological Estimation of Intracranial Blood Volume and Occurrence of Hydrocephalus Determines Stress-Induced Hyperglycemia After Aneurysmal Subarachnoid Hemorrhage

Acute phase after aneurysmal subarachnoid hemorrhage (aSAH) is associated with several metabolic derangements including stress-induced hyperglycemia (SIH). The present study is designed to identify objective radiological determinants for SIH to better understand its contributory role in clinical outcomes after aSAH. A computer-aided detection tool was used to segment admission computed tomography (CT) images of aSAH patients to estimate intracranial blood and cerebrospinal fluid volumes. Modified Graeb score (mGS) was used as a semi-quantitative measure to estimate degree of hydrocephalus. The relationship between glycemic gap (GG) determined SIH, mGS, and estimated intracranial blood and cerebrospinal fluid volumes were evaluated using linear regression. Ninety-four [94/187 (50.3%)] among the study cohort had SIH (defined as GG > 26.7 mg/dl). Patients with SIH had 14.3 ml/1000 ml more intracranial blood volume as compared to those without SIH [39.6 ml (95% confidence interval, CI, 33.6 to 45.5) vs. 25.3 ml (95% CI 20.6 to 29.9), p = 0.0002]. Linear regression analysis of mGS with GG showed each unit increase in mGS resulted in 1.2 mg/dl increase in GG [p = 0.002]. Patients with SIH had higher mGS [median 4.0, interquartile range, IQR 2.0-7.0] as compared to those without SIH [median 2.0, IQR 0.0-6.0], p = 0.002. Patients with third ventricular blood on admission CT scan were more likely to develop SIH [67/118 (56.8%) vs. 27/69 (39.1%), p = 0.023]. Hence, the present study, using unbiased SIH definition and objective CT scan parameters, reports "dose-dependent" radiological features resulting in SIH. Such findings allude to a brain injury-stress response-neuroendocrine axis in etiopathogenesis of SIH.

Stillbirth rates across three ape species in accredited American zoos

Stillbirths, or births of infants that died in the womb, represent a failure of the materno-feto-placental unit to maintain a suitable fetal environment. Typical studies of nonhuman primate (NHP) stillbirth patterns are primarily descriptive and focus on macaques (genus Macaca). Thus, less is known about other NHP species and rarer still are studies that examine possible biological factors that influence stillbirth rates across taxa. To examine possible contributors to stillbirths in great apes, we analyzed 36 years (1980-2016) of historical data documenting births of zoo-housed chimpanzees (Pan troglodytes, N = 391), western lowland gorillas (Gorilla gorilla gorilla, N = 491), and orangutans (Pongo spp, N = 307) in accredited zoological parks in the United States. The average number of births for each of the 446 mothers was 2.7, resulting in a total of 1,189 births with 143 stillbirths (12%). Stillbirths represented 12% of chimpanzee births, 13% of gorilla births, and 10% of orangutan births. We used generalized linear mixed-effects models to assess possible relationships between stillbirth likelihood and mother origin (wild- versus captive-born), age, and genus. Across taxa, older mothers were more likely to have a stillbirth (p = 0.004). While these results are likely influenced by both biological and management-related factors (e.g., selective captive breeding), they may be useful to population managers in evaluating pregnancy risks for great apes. Captive settings and archival studbook data such as these may provide a unique opportunity to further explore this topic.

An evaluation of video cameras for collecting observational data on sanctuary-housed chimpanzees (Pan troglodytes)

Video cameras are increasingly being used to monitor captive animals in zoo, laboratory, and agricultural settings. This technology may also be useful in sanctuaries with large and/or complex enclosures. However, the cost of camera equipment and a lack of formal evaluations regarding the use of cameras in sanctuary settings make it challenging for facilities to decide whether and how to implement this technology. To address this, we evaluated the feasibility of using a video camera system to monitor chimpanzees at Chimp Haven. We viewed a group of resident chimpanzees in a large forested enclosure and compared observations collected in person and with remote video cameras. We found that via camera, the observer viewed fewer chimpanzees in some outdoor locations (GLMM post hoc test: est. = 1.4503, SE = 0.1457, Z = 9.951, p < 0.001) and identified a lower proportion of chimpanzees (GLMM post hoc test: est. = -2.17914, SE = 0.08490, Z = -25.666, p < 0.001) compared to in-person observations. However, the observer could view the 2 ha enclosure 15 times faster by camera compared to in person. In addition to these results, we provide recommendations to animal facilities considering the installation of a video camera system. Despite some limitations of remote monitoring, we posit that there are substantial benefits of using camera systems in sanctuaries to facilitate animal care and observational research.

Abstract TP397: Modified Graeb Score Predicts Stress-Induced Hyperglycemia After Subarachnoid Hemorrhage

Introduction: Post-hemorrhagic hydrocephalus is a frequent complication after aneurysmal subarachnoid hemorrhage (aSAH) that can result in homeostatic derangement including stress induced hyperglycemia (SIH). Modified Graeb score (MGS) is a semi-quantitative scoring system that can estimate extent of hydrocephalus and amount of intraventricular blood.

Hypothesis: We assessed whether MGS can predict SIH after aSAH.

Methods: On the basis of our previous research with this same cohort, SIH was defined as a ratio of admission serum glucose (AG) to glycated hemoglobin, HbA1c (AG:HbA1c) of 26 or higher. This retrospective study reviewed charts of aSAH patients admitted to a tertiary care hospital. MGS was calculated retrospectively using admission computed tomography (CT) scans. Exploratory loess regression was used to characterize the association between MGS and SIH. Non-parametric tests were used to investigate difference in MGS between those with and without SIH. Fisher’s exact tests assessed differences in prevalence of SIH between patient groups.

Results: Average age of cohort was 52.3±13.1 years with 65% women. SIH was observed in 72/165 (43.6%) patients. One hundred and eight of the 165 patients (65.5%) were modified Fisher grade 3-4 on admission CT scans. Fifty-five patients (50.9%) with modified Fisher grade 3-4 developed SIH as compared to 17 (29.8%) of patients with modified Fisher grade 1-2 (p=0.013). Locally weighted or LOESS regression showed a positive relationship between the AG:HbA1c ratio at MGS up to about 12. MGS threshold of ≥10 predicted SIH with 88.2% specificity. Although median MGS was higher in patients developing SIH (4; interquartile range or IQR 5.5) as compared to those without SIH (2; IQR 6.0), the difference did not reach statistical significance (p=0.079).

Conclusion: Higher MGS, indicative of more severe obstructive hydrocephalus, is associated with increased incidence of SIH. This alludes to contribution of hydrocephalus in neurohumoral derangement and associated dysglycemia after aSAH.

Great ape walking kinematics: Implications for hominoid evolution

OBJECTIVES

Great apes provide a point of reference for understanding the evolution of locomotion in hominoids and early hominins. We assessed (1) the extent to which great apes use diagonal sequence, diagonal couplet gaits, like other primates, (2) the extent to which gait and posture vary across great apes, and (3) the role of body mass and limb proportions on ape quadrupedal kinematics.

METHODS

High-speed digital video of zoo-housed bonobos (Pan paniscus, N = 8), chimpanzees (Pan troglodytes, N = 13), lowland gorillas (Gorilla gorilla, N = 13), and orangutans (Pongo spp. N = 6) walking over-ground at self-selected speeds were used to determine the timing of limb touch-down, take-off, and to measure joint and segment angles at touch-down, midstance, and take-off.

RESULTS

The great apes in our study showed broad kinematic and spatiotemporal similarity in quadrupedal walking. Size-adjusted walking speed was the strongest predictor of gait variables. Body mass had a negligible effect on variation in joint and segment angles, but stride frequency did trend higher among larger apes in analyses including size-adjusted speed. In contrast to most other primates, great apes did not favor diagonal sequence footfall patterns, but exhibited variable gait patterns that frequently shifted between diagonal and lateral sequences.

CONCLUSION

Similarities in the terrestrial walking kinematics of extant great apes likely reflect their similar post-cranial anatomy and proportions. Our results suggest that the walking kinematics of orthograde, suspensory Miocene ape species were likely similar to living great apes, and highlight the utility of videographic and behavioral data in interpreting primate skeletal morphology.

Social Models Enhance Apes' Memory for Novel Events

Nonhuman primates are more likely to learn from the actions of a social model than a non-social "ghost display", however the mechanism underlying this effect is still unknown. One possibility is that live models are more engaging, drawing increased attention to social stimuli. However, recent research with humans has suggested that live models fundamentally alter memory, not low-level attention. In the current study, we developed a novel eye-tracking paradigm to disentangle the influence of social context on attention and memory in apes. Tested in two conditions, zoo-housed apes (2 gorillas, 5 chimpanzees) were familiarized to videos of a human hand (social condition) and mechanical claw (non-social condition) constructing a three-block tower. During the memory test, subjects viewed side-by-side pictures of the previously-constructed block tower and a novel block tower. In accordance with looking-time paradigms, increased looking time to the novel block tower was used to measure event memory. Apes evidenced memory for the event featuring a social model, though not for the non-social condition. This effect was not dependent on attention differences to the videos. These findings provide the first evidence that, like humans, social stimuli increase nonhuman primates' event memory, which may aid in information transmission via social learning.

Assessment of behavior and space use before and after forelimb amputation in a zoo-housed chimpanzee (Pan troglodytes)

Primates possess great manual dexterity, and their limbs are integral to many aspects of normal functioning (e.g., climbing, feeding). As such, the loss of a limb carries the risk of significant disability and potentially harmful impairment of species-typical functioning. Limb loss is known to occur in some wild primate populations due to entanglement in hunting snares, but can also occur in captive settings due to injury that necessitates therapeutic amputation. In this study, we conducted a detailed evaluation of the behavior, travel, and space use expressed by a female zoo-housed chimpanzee (Pan troglodytes) before and following surgical amputation of her right forelimb. Overall, our results suggest that the injury did not substantively affect her daily activities. She showed no change to her vertical space use, spending equivalent proportions of her time on the ground and high in the enclosure. There was a decrease in the frequency of locomotion on the ground (P = 0.006) but also a significant increase in the overall distance travelled (P = 0.0015) following the removal of the limb. This case study provides evidence that individual chimpanzees are able to successfully adjust to significant anatomical changes when provided adequate environments in which to stay active, and highlights the importance of an effective post-surgical monitoring period-a comprehensive recovery evaluation that includes input from both veterinary and behavioral research staff is likely to provide the most holistic assessment of animal health and long-term wellbeing. Zoo Biol. 36:5-10, 2017. © 2016 Wiley Periodicals, Inc.

Characterizing abnormal behavior in a large population of zoo-housed chimpanzees: prevalence and potential influencing factors

Abnormal behaviors in captive animals are generally defined as behaviors that are atypical for the species and are often considered to be indicators of poor welfare. Although some abnormal behaviors have been empirically linked to conditions related to elevated stress and compromised welfare in primates, others have little or no evidence on which to base such a relationship. The objective of this study was to investigate a recent claim that abnormal behavior is endemic in the captive population by surveying a broad sample of chimpanzees (Pan troglodytes), while also considering factors associated with the origins of these behaviors. We surveyed animal care staff from 26 accredited zoos to assess the prevalence of abnormal behavior in a large sample of chimpanzees in the United States for which we had information on origin and rearing history. Our results demonstrated that 64% of this sample was reported to engage in some form of abnormal behavior in the past two years and 48% of chimpanzees engaged in abnormal behavior other than coprophagy. Logistic regression models were used to analyze the historical variables that best predicted the occurrence of all abnormal behavior, any abnormal behavior that was not coprophagy, and coprophagy. Rearing had opposing effects on the occurrence of coprophagy and the other abnormal behaviors such that mother-reared individuals were more likely to perform coprophagy, whereas non-mother-reared individuals were more likely to perform other abnormal behaviors. These results support the assertion that coprophagy may be classified separately when assessing abnormal behavior and the welfare of captive chimpanzees. This robust evaluation of the prevalence of abnormal behavior in our sample from the U.S. zoo population also demonstrates the importance of considering the contribution of historical variables to present behavior, in order to better understand the causes of these behaviors and any potential relationship to psychological wellbeing.

Behavioral research as physical enrichment for captive chimpanzees

In this study, we evaluated the potential for a behavioral research study, designed to evaluate chimpanzee decision-making behavior, to also encourage increased activity in a group of zoo-housed chimpanzees. For the behavioral study, the chimpanzees had to carry tokens to different locations such that they always had to travel farther to obtain a more-preferred reward. We recorded the distance travelled by each subject in each of the three phases of the 15-month study. By the final phase, the chimpanzees' rate of travel during test sessions was significantly higher compared to their baseline activity. Importantly, the chimpanzees' increase in locomotion was not dependent on their participation in the study; rate of travel was not correlated with number of tokens exchanged. However, the chimpanzees' activity returned to baseline within 2 hr of the 30-min test sessions. This study emphasizes the role that research can have in providing enrichment, the importance for long-term enrichment plans, and the essential need to evaluate the impact of research on animal participants, just as we evaluate the efficacy of enrichment strategies. Zoo Biol. 35:293-297, 2016. © 2016 Wiley Periodicals, Inc.

Metabolic acceleration and the evolution of human brain size and life history

Humans are distinguished from the other living apes in having larger brains and an unusual life history that combines high reproductive output with slow childhood growth and exceptional longevity. This suite of derived traits suggests major changes in energy expenditure and allocation in the human lineage, but direct measures of human and ape metabolism are needed to compare evolved energy strategies among hominoids. Here we used doubly labelled water measurements of total energy expenditure (TEE; kcal day(-1)) in humans, chimpanzees, bonobos, gorillas and orangutans to test the hypothesis that the human lineage has experienced an acceleration in metabolic rate, providing energy for larger brains and faster reproduction without sacrificing maintenance and longevity. In multivariate regressions including body size and physical activity, human TEE exceeded that of chimpanzees and bonobos, gorillas and orangutans by approximately 400, 635 and 820 kcal day(-1), respectively, readily accommodating the cost of humans' greater brain size and reproductive output. Much of the increase in TEE is attributable to humans' greater basal metabolic rate (kcal day(-1)), indicating increased organ metabolic activity. Humans also had the greatest body fat percentage. An increased metabolic rate, along with changes in energy allocation, was crucial in the evolution of human brain size and life history.

Brief Report: Chimpanzee Social Responsiveness Scale (CSRS) Detects Individual Variation in Social Responsiveness for Captive Chimpanzees

Comparative studies of social responsiveness, a core impairment in autism spectrum disorder (ASD), will enhance our understanding of typical and atypical social behavior. We previously reported a quantitative, cross-species (human-chimpanzee) social responsiveness measure, which included the development of the Chimpanzee Social Responsiveness Scale (CSRS). Here, we augment our prior CSRS sample with 25 zoo chimpanzees at three sites: combined N = 54. The CSRS demonstrated strong interrater reliability, and low-ranked chimpanzees, on average, displayed higher CSRS scores. The CSRS continues to discriminate variation in chimpanzee social responsiveness, and the association of higher scores with lower chimpanzee social standing has implications for the relationship between autistic traits and human social status. Continued comparative investigations of social responsiveness will enhance our understanding of underlying impairments in ASD, improve early diagnosis, and inform future therapies.

Western lowland gorilla (Gorilla gorilla gorilla) birth patterns and human presence in zoological settings

There is some evidence to suggest that zoo visitors may have a disruptive impact on zoo-housed animals, especially primates. While some consider western lowland gorillas (Gorilla gorilla gorilla) to be particularly reactive to large crowds, the evidence of these effects is mixed, and is likely highly influenced by exhibit design, and group composition. While the majority of studies have focused on behavioral responses to human presence, there is the potential for physiological effects as well, including the possibility of affecting the timing of parturition. Such effects have been demonstrated in laboratory-housed callitrichids and chimpanzees, but unlike laboratory settings where human presence is lowest during the weekends, human presence might peak during weekends in public zoo settings. However, in a study of zoo-housed chimpanzees, there were no significant differences between the number of chimpanzee births that occurred on weekdays compared to weekends [Wagner and Ross, 2008], and we sought to test these questions with gorillas. We analyzed the timing of 336 live gorilla births and 48 stillbirths at 53 accredited North American zoos from 1985-2014, and similarly to chimpanzees, found no weekend or weekday effect on number of births (live births: G = 0.000, p = 1; stillbirths: G = 0.166, p < 0.684). These data add to our understanding of the potential influence of human presence on primate behavior and physiology, and add to evidence suggesting that the effects of zoo visitors on exhibited species may be less profound than previously assumed.

Captive chimpanzee foraging in a social setting: a test of problem solving, flexibility, and spatial discounting

In the wild, primates are selective over the routes that they take when foraging and seek out preferred or ephemeral food. Given this, we tested how a group of captive chimpanzees weighed the relative benefits and costs of foraging for food in their environment when a less-preferred food could be obtained with less effort than a more-preferred food. In this study, a social group of six zoo-housed chimpanzees (Pan troglodytes) could collect PVC tokens and exchange them with researchers for food rewards at one of two locations. Food preference tests had revealed that, for these chimpanzees, grapes were a highly-preferred food while carrot pieces were a less-preferred food. The chimpanzees were tested in three phases, each comprised of 30 thirty-minute sessions. In phases 1 and 3, if the chimpanzees exchanged a token at the location they collected them they received a carrot piece (no travel) or they could travel ≥10 m to exchange tokens for grapes at a second location. In phase 2, the chimpanzees had to travel for both rewards (≥10 m for carrot pieces, ≥15 m for grapes). The chimpanzees learned how to exchange tokens for food rewards, but there was individual variation in the time it took for them to make their first exchange and to discover the different exchange locations. Once all the chimpanzees were proficient at exchanging tokens, they exchanged more tokens for grapes (phase 3). However, when travel was required for both rewards (phase 2), the chimpanzees were less likely to work for either reward. Aside from the alpha male, all chimpanzees exchanged tokens for both reward types, demonstrating their ability to explore the available options. Contrary to our predictions, low-ranked individuals made more exchanges than high-ranked individuals, most likely because, in this protocol, chimpanzees could not monopolize the tokens or access to exchange locations. Although the chimpanzees showed a preference for exchanging tokens for their more-preferred food, they appeared to develop strategies to reduce the cost associated with obtaining the grapes, including scrounging rewards and tokens from group mates and carrying more than one token when travelling to the farther exchange location. By testing the chimpanzees in their social group we were able to tease apart the social and individual influences on their decision making and the interplay with the physical demands of the task, which revealed that the chimpanzees were willing to travel farther for better.

Impact of visual context on public perceptions of non-human primate performers

Prior research has shown that the use of apes, specifically chimpanzees, as performers in the media negatively impacts public attitudes of their conservation status and desirability as a pet, yet it is unclear whether these findings generalize to other non-human primates (specifically non-ape species). We evaluated the impact of viewing an image of a monkey or prosimian in an anthropomorphic or naturalistic setting, either in contact with or in the absence of a human. Viewing the primate in an anthropomorphic setting while in contact with a person significantly increased their desirability as a pet, which also correlated with increased likelihood of believing the animal was not endangered. The majority of viewers felt that the primates in all tested images were "nervous." When shown in contact with a human, viewers felt they were "sad" and "scared", while also being less "funny." Our findings highlight the potential broader implications of the use of non-human primate performers by the entertainment industry.

The impact of atypical early histories on pet or performer chimpanzees

It is widely accepted that an animal's early history, including but not limited to its rearing history, can have a profound impact on later behavior. In the case of captive animals, many studies have used categorical measures such as mother reared or human reared that do not account for both the influence of human and conspecific interaction. In order to account for the influence of both human and conspecific early exposure to later behavior, we collected 1385 h of data on 60 chimpanzees, of which 36 were former pets or performers, currently housed at accredited zoos or sanctuaries. We developed a unique metric, the Chimpanzee-Human Interaction (CHI) Index that represented a continuous measure of the proportion of human and chimpanzee exposure subjects experienced and here focused on their exposure during the first four years of life. We found that chimpanzees who experienced less exposure to other chimpanzees as infants showed a lower frequency of grooming and sexual behaviors later in life which can influence social dynamics within groups. We also found chimpanzees who experienced more exposure to other chimpanzees as infants showed a higher frequency of coprophagy, suggesting coprophagy could be a socially-learned behavior. These results help characterize some of the long-term effects borne by chimpanzees maintained as pets and performers and may help inform managers seeking to integrate these types of chimpanzees into larger social groups, as in zoos and sanctuaries. In addition, these results highlight the necessity of taking into account the time-weighted influence of human and conspecific interactions when assessing the impact that humans can have on animals living in captivity.

Chimpanzees create and modify probe tools functionally: A study with zoo-housed chimpanzees

Chimpanzees (Pan troglodytes) use tools to probe for out-of-reach food, both in the wild and in captivity. Beyond gathering appropriately-sized materials to create tools, chimpanzees also perform secondary modifications in order to create an optimized tool. In this study, we recorded the behavior of a group of zoo-housed chimpanzees when presented with opportunities to use tools to probe for liquid foods in an artificial termite mound within their enclosure. Previous research with this group of chimpanzees has shown that they are proficient at gathering materials from within their environment in order to create tools to probe for the liquid food within the artificial mound. Extending beyond this basic question, we first asked whether they only made and modified probe tools when it was appropriate to do so (i.e. when the mound was baited with food). Second, by collecting continuous data on their behavior, we also asked whether the chimpanzees first (intentionally) modified their tools prior to probing for food or whether such modifications occurred after tool use, possibly as a by-product of chewing and eating the food from the tools. Following our predictions, we found that tool modification predicted tool use; the chimpanzees began using their tools within a short delay of creating and modifying them, and the chimpanzees performed more tool modifying behaviors when food was available than when they could not gain food through the use of probe tools. We also discuss our results in terms of the chimpanzees' acquisition of the skills, and their flexibility of tool use and learning.