Diet traditions in wild orangutans

This study explores diet differences between two populations of wild Bornean orangutans (Pongo pygmaeus wurmbii) to assess whether a signal of social learning can be detected in the observed patterns. The populations live in close proximity and in similar habitats but are separated by a river barrier that is impassable to orangutans in the study region. We found a 60% between‐site difference in diet at the level of plant food items (plant species–organ combinations). We also found that individuals at the same site were more likely to eat the same food items than expected by chance. These results suggest the presence of diet (food selection) traditions. Detailed tests of three predictions of three models of diet acquisition allowed us to reject a model based on exclusive social learning but could not clearly distinguish between the remaining two models: one positing individual exploration and learning of food item selection and the other one positing preferential social learning followed by individual fine tuning. We know that maturing orangutans acquire their initial diet through social learning and then supplement it by years of low‐level, individual sampling. We, therefore, conclude that the preferential social learning model produces the best fit to the geographic patterns observed in this study. However, the very same taxa that socially acquire their diets as infants and show evidence for innovation‐based traditions in the wild paradoxically may have diets that are not easily distinguished from those acquired exclusively through individual learning. Am J Phys Anthropol 143:175–187, 2010. © 2010 Wiley‐Liss, Inc.     

Immature wild orangutans acquire relevant ecological knowledge through sex-specific attentional biases during social learning

As a part of growing up, immature orangutans must acquire vast repertoires of skills and knowledge, a process that takes several years of observational social learning and subsequent practice. Adult female and male orangutans show behavioral differences including sex-specific foraging patterns and male-biased dispersal. We investigated how these differing life trajectories affect social interest and emerging ecological knowledge in immatures. We analyzed 15 years of detailed observational data on social learning, associations, and diet repertoires of 50 immatures (16 females and 34 males), from 2 orangutan populations. Specific to the feeding context, we found sex differences in the development of social interest: Throughout the dependency period, immature females direct most of their social attention at their mothers, whereas immature males show an increasing attentional preference for individuals other than their mothers. When attending to non-mother individuals, males show a significant bias toward immigrant individuals and a trend for a bias toward adult males. In contrast, females preferentially attend to neighboring residents. Accordingly, by the end of the dependency period, immature females show a larger dietary overlap with their mothers than do immature males. These results suggest that immature orangutans show attentional biases through which they learn from individuals with the most relevant ecological knowledge. Diversifying their skills and knowledge likely helps males when they move to a new area. In sum, our findings underline the importance of fine-grained social inputs for the acquisition of ecological knowledge and skills in orangutans and likely in other apes as well.

To understand the development and evolution of cognition of our closest relatives, we need to investigate their learning behavior during every-day life. This study finds that wild orangutan males and females differ in their social learning strategies and subsequent learning outcomes from an early age, underlining the general importance of, and the effects of sex on, social learning in non-human great apes.     

Begging for information: mother-offspring food sharing among wild Bornean orangutans

Transfer of solid food from mothers or other adults to dependent offspring is commonly observed in various primate species and both nutritional and informational benefits have been proposed to explain the function of such food sharing. Predictions from these hypotheses are tested using observational data on wild orangutans (Pongo pygmaeus wurmbii) at Tuanan, Central Borneo, Indonesia. In 1,145 hr of focal observation and 458 recorded food interactions between four pairs of females with offspring it was found that virtually all transfers were initiated by the offspring and that younger infants solicited food more often and did so for a greater variety of items than older offspring. All offspring primarily solicited food that was difficult to process, i.e., inaccessible to them. Furthermore, the amount of food solicitation was negatively correlated with ecological competence. Hence food sharing seemed to be related to an offspring's skill level, as suggested by the informational hypothesis. In contrast, offspring did not solicit high-quality items more than low-quality items and food sharing did not peak around the age of weaning, as predicted by the nutritional hypothesis. Mothers were usually passively tolerant, allowing offspring to take food but hardly ever provisioned. Parent-offspring conflict concerning food sharing was only observed well after weaning. Thus, by taking food directly from the mother, young orangutans were able to obtain information about the affordances and nutritional value of food items that were otherwise out of their reach and could familiarize themselves with the mother's diet. In species such as orangutans or other apes, characterized by a broad diet that requires extractive foraging, informational food transfer may be vital for an immature to acquire complex feeding skills and adult diet.     

Adaptation to Forest Life During the Reintroduction Process of Immature <Emphasis Type="Italic">Pongo abelii</Emphasis>

Reintroduction of Sumatran orangutans can be an important tool to conserve the species in the face of the current decline of wild populations. Monitoring ex-captive orangutans during the reintroduction process provides insight into their adaptation to forest life and is important for evaluating the success of such programs. We investigated activity patterns, food choice, height use, and nest-building abilities of 8 immature orangutans at a reintroduction station in Sumatra. All focal individuals spent most of their time in the forest feeding, but at a lower proportion than wild conspecifics. Among the focal individuals, the behavior of orangutans that avoided human contact differed in several aspects from those that were human bonded. Their diet was composed mainly of fruits, similar to the food choice of wild orangutans, and their ground-avoidance and superior nest-building abilities indicated more effective predation-avoidance behavior vs. that of human-bonded animals. Finally, these immatures showed regular social contact with more experienced conspecifics, which ultimately may facilitate the social learning of local feral expertise. Human-bonded individuals, in contrast, preferentially stayed on the ground and at low heights and rarely built nests, thereby increasing predation risk. Their choice of leaves over fruits as foods indicated a less effective foraging strategy. Nevertheless, this group exhibited individual learning trends toward an adult-like foraging pattern and height use. We conclude that social interactions with conspecifics and humans, especially during an early developmental period, can affect adaptation to forest life and probably also influence the success of orangutan reintroduction processes.     

Maternal influence on the development of nut‐cracking skills in the chimpanzees of the Taï forest,Côte d'Ivoire (Pan troglodytes verus)

Chimpanzees’ (Pan troglodytes) nut‐cracking behavior represents one of the most complex forms of tool‐use known among nonhuman animals. Given the close phylogenetic relationship between these apes and humans, investigating how such complex behavior develops in immatures can reveal the evolutionary roots of the cognitive processes that enabled the evolution of outstanding technological skills in our lineage. In this study, we investigated whether maternal behavior directly enhanced nut‐cracking skills in immature individuals. We analyzed the behavior of 11 immatures and their mothers (N = 8) during nut‐cracking activity, spanning over three consecutive nut‐cracking seasons in the Taï National Park, Côte d'Ivoire. We used generalized linear mixed models to (a) obtain values of maternal scaffolding (defined as provision of learning opportunities) and active nut‐sharing behavior of each mother according to the age of their offspring, and their average nut‐cracking efficiency; (b) to test whether these variables enhanced immatures’ nut‐cracking skills; and (c) to test whether immatures’ features (age, sex, and begging behavior) influenced maternal behavior as observed in our videos. Although the predicted values of maternal scaffolding and active nut‐sharing did not obviously affect immatures’ skills, they were positively influenced by the average maternal efficiency and by sharing hammers with their mothers. In addition, our observations showed that mothers were more likely to share nuts with their sons than with their daughters, and the more their offspring begged. Concurrently, male immatures were also found to beg more often than females. Our results add evidence on the ontogenetic pathway leading to the full acquisition of nut‐cracking in wild chimpanzees and on the effect that maternal behavior can have in promoting the acquisition of this complex tool‐use behavior. Moreover, our study strengthens the importance of naturalistic observations to understand complex skill acquisition. Finally, we suggest future avenues for investigating the maternal influence on learning.     

Co–Residence between Males and Their Mothers and Grandmothers Is More Frequent in Bonobos Than Chimpanzees

In long–lived social mammals such as primates, individuals can benefit from social bonds with close kin, including their mothers. In the patrilocal chimpanzee (Pan troglodytes spp.) and bonobo (Pan paniscus), sexually mature males reside and reproduce in their natal groups and can retain post-dependency bonds with their mothers, while immatures of both sexes might also have their paternal grandmothers available. However, quantitative information on the proportion of males and immatures that co-reside with both types of these close female relatives is limited for both species. Combining genetic parentage determination and group composition data from five communities of wild chimpanzees and three communities of wild bonobos, we estimated the frequency of co-residence between (1) mature males and their mothers, and (2) immature males and females and their paternal grandmothers. We found that adult males resided twice as frequently with their mothers in bonobos than in chimpanzees, and that immature bonobos were three times more likely to possess a living paternal grandmother than were immature chimpanzees. Patterns of female and male survivorship from studbook records of captive individuals of both species suggest that mature bonobo females survive longer than their chimpanzee counterparts, possibly contributing to the differences observed in mother–son and grandmother–immature co-residency levels. Taking into account reports of bonobo mothers supporting their sons'' mating efforts and females sharing food with immatures other than their own offspring, our findings suggest that life history traits may facilitate maternal and grandmaternal support more in bonobos than in chimpanzees.     

Food Neophobia and Social Learning Opportunities in Great Apes

Finding food resources and maintaining a balanced diet are major concerns for all animals. A compromise between neophobia and neophilia is hypothesised to enable animals to enlarge their diet while limiting the risk of poisoning. However, little is known about how primates respond to novel food items and whether their use is socially transmitted. By comparing how four different species of great apes respond to novel food items, we investigated how differences in physiology (digestive tract size and microbial content), habitats (predictability of food availability), and social systems (group size and composition) affect their response toward novelty. We presented two familiar foods, one novel fruit, four novel aromatic plants from herbal medicine, and kaolin to captive chimpanzees (Pan troglodytes), western gorillas (Gorilla gorilla), Bornean orangutans (Pongo pygmaeus) and Sumatran orangutans (Pongo abelii). We recorded smelling, approach-taste delays, ingestion, interindividual observations, and food transfers with continuous sampling. We found that behaviors differed between the apes: chimpanzees were the most cautious species and observed their conspecifics handling the items more frequently than the other apes. Close observations and food transfers were extremely rare in gorillas in comparison to orangutans and chimpanzees. We suggest that a low neophobia level reflects an adaptive response to digestive physiological features in gorillas and to unpredictable food availability in orangutans. Social interactions appeared to be predominant in chimpanzees and in both orangutan species to overcome food neophobia. They reflect higher social tolerance and more opportunities for social learning and cultural transmission in a feeding context.     

The conditions for tool use in primates: implications for the evolution of material culture

In order to identify the conditions that favored the flourishing of primate tool use into hominid technology, we examine inter- and intraspecific variation in manufacture and use of tools in extant nonhuman primates, and develop a model to account for their distribution. We focus on tools used in acquiring food, usually by extraction. Any model for the evolution of the use of feeding tools must explain why tool use is found in only a small subset of primate species, why many of these species use tools much more readily in captivity, why routine reliance on feeding tools is found in only two species of ape, and why there is strong geographic variation within these two species. Because ecological factors alone cannot explain the distribution of tool use in the wild, we develop a model that focuses on social and cognitive factors affecting the invention and transmission of tool-using skills. The model posits that tool use in the wild depends on suitable ecological niches (especially extractive foraging) and the manipulative skills that go with them, a measure of intelligence that enables rapid acquisition of complex skills (through both invention and, more importantly, observational learning), and social tolerance in a gregarious setting (which facilitates both invention and transmission). The manipulative skills component explains the distribution across species of the use of feeding tools, intelligence explains why in the wild only apes are known to make and use feeding tools routinely, and social tolerance explains variation across populations of chimpanzees and orangutans. We conclude that strong mutual tolerance was a key factor in the explosive increase in technology among hominids, probably intricately tied to a lifestyle involving food sharing and tool-based processing or the acquisition of large, shareable food packages.     

Associative learning in immature lacewings (Ceraeochrysa cubana)

It is known that many social insects and arthropod predators and parasitoids can learn the association between a resource and volatile cues. Although there are various studies on the effect of experience in immature arthropods on behavior later in adult life, not much is known about the effects of such experiences on immature behavior. This was investigated here in the lacewing Ceraeochrysa cubana (Hagen) (Neuroptera: Chrysopidae). Whereas adults of this lacewing feed on plant‐provided food and honeydew, larvae are voracious polyphagous predators of several insect pests, and therefore important for biological control. Hence, studying the foraging behavior and the effects of learning in immatures of this species is important. We exposed immatures to the volatile methyl salicylate (MeSA), which was either associated with food or with the absence of food. Subsequently, their response to this volatile was tested in an olfactometer. Immatures that had experienced the association of MeSA with food were attracted to it and immatures that were exposed to MeSA during food deprivation were repelled. Subsequently, predator immatures that had experienced the association between MeSA and food were released on a plant without food and were found to use this volatile in locating patches with food. In contrast, larvae without such experience were found equally on food patches with and without the volatile. We conclude that these immature predators are capable of learning the association between volatiles and food, or the absence of food, and use this during foraging.     

Observational learning in orangutan cultural transmission chains

Field reports suggest that orangutans acquire local traditions by observing neighbouring conspecifics. However, there is little direct evidence of social learning to support this conclusion. The present study investigated whether orangutans would learn a novel foraging method through observation of a conspecific in a diffusion-chain paradigm testing for the spread of the behaviour. A foraging box with two possible methods for extracting food was used to investigate the transmission of a foraging tradition among zoo-living subjects. In a socially housed group of five orangutans, the dominant male was trained to use one technique exclusively to retrieve food. He then performed this technique in the presence of another group member, who was then allowed to forage. After several trials, the observer became the model for the next individual. A second experimental group of six individuals was introduced to the alternative method. The model-seeded technique was successfully transmitted along both experimental chains, with significant preferences for the model method. These results are consistent with claims for social transmission of foraging methods in wild orangutans.     

Maternal and paternal controlling feeding practices: reliability and relationships with BMI

Objective: This study aimed to examine the interrelationships between mothers' and fathers' reports on the child‐feeding questionnaire (CFQ), the BMI of parents and their children, and observations of parents' controlling feeding practices at mealtimes. Methods and Procedures: Twenty‐three mothers and twenty‐three fathers of children aged between 18 and 67 months reported on their child‐feeding practices, on their child's height and weight, and were observed during a normal family mealtime at home. Results: No associations were found between mothers' reported and observed feeding practices. Fathers' reported pressure to eat and restriction were associated with more controlling observed mealtime feeding practices. Mothers and fathers did not significantly differ in their reported or observed child‐feeding practices. Children's BMI was not related to maternal or paternal reported or observed feeding practices. More mealtime pressure was observed in parents with a higher BMI. Discussion: Fathers' self‐reports of their mealtime practices are reliable. Mothers' feeding practices may differ when fathers are present and further work should examine mothers at mealtimes with and without fathers. Although children's BMI was not related to parents' use of reported or observed control, parents with a higher BMI were more controlling, highlighting the importance of considering parents' own weight in future studies.     

Development of ecological competence in Sumatran orangutans

Data on orangutans (Pongo pygmaeus abelii) living in a Sumatran swamp forest yield an estimated median interbirth interval of at least 8 years, concurring with findings from other sites. This longest known mammalian interbirth interval appears due to maternal amenorrhea during the long exclusive dependence of the offspring. We describe the development of various components of offspring independence. In this arboreal ape, 3‐year‐olds had largely reached locomotor independence. Nest‐building skills were also well‐developed in 3‐year‐olds, but immatures shared their mother's nest until weaned at around age 7. At time of birth of the new sibling, association with the mother had begun to decline for both male and female offspring, suggesting that the immatures had mastered all the necessary skills, including basic tool use, to feed themselves. By about 11 years of age, they also ranged independently from the mother. These results show that orangutans do not develop independence more slowly than chimpanzees. Why, then, is weaning 2 years later in orangutans? In chimpanzees, mothers are often accompanied by two or even three consecutive offspring, unlike in orangutans. This contrast suggests that an orangutan mother cannot give birth until the previous offspring is ecologically competent enough to begin to range independently of her, probably due to the high energy costs of association. Thus, the exceptionally long interbirth intervals of orangutans may be a consequence of their solitary lifestyle. Am J Phys Anthropol, 2004. © 2004 Wiley‐Liss, Inc.     

Individual variation in nest size and nest site features of the Bornean orangutans (Pongo pygmaeus)

Nest construction is a daily habit of independent orangutans for sleeping or resting. Data on their nests have been used in various ecological studies (e.g., density estimation, ranging behavior, evolution of material culture) because they are the most observable field signs. We investigated nest size and nest site features of Bornean orangutans in the wild during 10 months' fieldwork at three sites in East Kalimantan, Indonesia: Kutai National Park, Birawa, and Meratus. To examine individual variation, we followed 31 individual orangutans and recorded the 92 nests they made for nest size (diameter) and nest site features (height of nest above ground, tree species used for the nest site, the diameter and height of the tree, whether the nest was new or reused, and nest location within the tree). Analyses taking age–sex classes of the focal individuals into consideration showed significant age–sex differences in nest size and location, but not in nest height or nest tree features (diameter, height of tree, and height of lowest branch). Mature orangutans (adult females, unflanged and flanged males) made larger nests than immatures (juveniles and adolescents). Flanged male orangutans with larger nests used stable locations for nesting sites and reused old nests more frequently than immatures. The overall proportion of nests in open (exposed) locations was higher than in closed (sheltered) locations. Flanged males and immatures frequently made open nests, whereas adult females with an infant preferred closed locations. The good correspondence between nest size and age–sex classes indicates that nest size variation may reflect body size and therefore age–sex variation in the population. Am. J. Primatol. 71:393–399, 2009. © 2009 Wiley‐Liss, Inc.     

灵长类动物的食物分享行为

食物分享是灵长类动物的一种重要社会交往行为,主要发生在成体-幼体间和成体-成体之间。本文从这两个方面对灵长类动物食物分享的行为表现、特点以及功能进行总结,着重比较了无亲缘关系的成年个体间食物分享的互惠解释和骚扰解释。通过对以上内容的综合分析,进一步提出了食物分享行为的未来研究方向以及对人类合作行为演化的启示。     

The ontogeny of handling hard‐to‐process food in wild brown capuchins (Cebus apella apella): evidence from foraging on the fruit of Maximiliana maripa

We examined age‐related differences in wild brown capuchins' foraging efficiency and the food‐processing behaviors directed toward maripa palm fruit (Maximiliana maripa). A detailed comparison of the different foraging techniques showed that plucking the fruit from the infructescence constituted the main difficulty of this task. Foraging efficiency tended to increase with age, with a threshold at which sufficient strength allowed immatures by the age of three to reach adult‐level efficiency. Youngsters spent more time than older individuals browsing the infructescence and pulling the fruit in an attempt to harvest it. Infants tried to compensate for their inability to pluck fruit by adopting alternative strategies but with low payback, such as gnawing unplucked fruit and opportunistically scrounging others' partially processed food. Although around 2 years of age, young capuchins exhibited all of the behaviors used by adults, they did not reach adult‐level proficiency at feeding on maripa until about 3 years (older juveniles). We compared this developmental pattern with that of extractive foraging on beetle larvae (Myelobia sp.) hidden in bamboo stalks, a more difficult food for these monkeys [Gunst N, Boinski S, Fragaszy DM. Behaviour 145:195–229, 2008]. For maripa, the challenge was mainly physical (plucking the fruit) once a tree was encountered, whereas for larvae, the challenge was primarily perceptual (locating the hidden larvae). For both foods, capuchins practice for years before achieving adult‐level foraging competence, and the timeline is extended for larvae foraging (until 6 years) compared with maripa (3 years). The differing combinations of opportunities and challenges for learning to forage on these different foods illustrate how young generalist foragers (i.e. exploiting a large number of animal and plant species) may compensate for their low efficiency in extractive foraging tasks by showing earlier competence in processing less difficult but nutritious foods, such as maripa fruit. Am. J. Primatol. 72:960–973, 2010. © 2010 Wiley‐Liss, Inc.     

A model for tool-use traditions in primates: implications for the coevolution of culture and cognition

Inspired by the demonstration that tool-use variants among wild chimpanzees and orangutans qualify as traditions (or cultures), we developed a formal model to predict the incidence of these acquired specializations among wild primates and to examine the evolution of their underlying abilities. We assumed that the acquisition of the skill by an individual in a social unit is crucially controlled by three main factors, namely probability of innovation, probability of socially biased learning, and the prevailing social conditions (sociability, or number of potential experts at close proximity). The model reconfirms the restriction of customary tool use in wild primates to the most intelligent radiation, great apes; the greater incidence of tool use in more sociable populations of orangutans and chimpanzees; and tendencies toward tool manufacture among the most sociable monkeys. However, it also indicates that sociable gregariousness is far more likely to produce the maintenance of invented skills in a population than solitary life, where the mother is the only accessible expert. We therefore used the model to explore the evolution of the three key parameters. The most likely evolutionary scenario is that where complex skills contribute to fitness, sociability and/or the capacity for socially biased learning increase, whereas innovative abilities (i.e., intelligence) follow indirectly. We suggest that the evolution of high intelligence will often be a byproduct of selection on abilities for socially biased learning that are needed to acquire important skills, and hence that high intelligence should be most common in sociable rather than solitary organisms. Evidence for increased sociability during hominin evolution is consistent with this new hypothesis.     

Provisioning of Young in Golden Lion Tamarins (Callitrichidae, Leontopithecus rosalia): A Test of the Information Hypothesis

Provisioning of young after weaning or fledging is a highly variable phenomenon. Among cooperative breeders, such as marmosets and tamarins, both parents and natal adults may provision immatures. Experiments designed to measure the effects of food familiarity on food-transfer interactions were conducted on zoo-living golden lion tamarin, Leontopithecus rosalia , families to test one proposed benefit of provisioning to recipient young — that immature callitrichids learn food preferences through exposure to food items obtained from older group members. Adults transferred to immatures foods that were known to adults, but novel to immatures, and foods that were novel to all more frequently than foods that were familiar to both adults and immatures. Results suggest that adults alter their behavior such that learning by immatures is fostered. Immatures also were less likely to reject new foods acquired from other group members, compared with those obtained independently, suggesting the possibility that immatures attend to food transfer to facilitate incorporation of new foods into the diet. In contrast, anecdotal accounts of wild marmoset and tamarin food transfer have indicated that infants receive from adults foods that primarily are high in lipids and/or protein, as expected if provisioning acts to supplement nutrition. These apparently contradictory findings may reflect the differing effects of the captive and wild environment on food-transfer behavior or may point to a dual function of provisioning dependent on age of the recipient.     

An evaluation of the geographic method for recognizing innovations in nature,using zoo orangutans

Innovation and social learning are the raw materials for traditions and culture. Of these two, innovation has received far less scrutiny, largely because of difficulties assessing the innovation status of behaviors. A recent attempt proposes recognition of innovations in natural populations based on assessment of the behavior’s properties and its geographic and local prevalence. Here we examine the validity of this approach and the list of 43 potential innovations it generated for wild orangutans by extending the comparison to zoo orangutans. First, we created an inventory of the behavioral repertoire in the zoo population. Four of ten putative innovations recognized in the field and potentially present in captivity did not occur despite appropriate conditions, suggesting they are indeed innovations. Second, we experimentally produced relevant conditions to evaluate whether another five potential innovations could be elicited. Based on their continued absence or on their latencies relative to known behaviors, four of the potential innovations could be assessed as innovations and one as a modification. Because 53% of relevant innovations recognized in the field could be confirmed in this analysis, and another 27% assigned possible innovation status, we conclude that the geographic method for detecting innovation in the wild is valid. However, the experiments also yielded up to 13 additional innovations, suggesting that zoo orangutans are far more innovative than wild ones. We discuss the implications of this latter finding with regard to limiting factors for the expansion of cultural repertoires in wild orangutans.     

Development of foraging skills in two orangutan populations: needing to learn or needing to grow?

Background

Orangutans have one of the slowest-paced life histories of all mammals. Whereas life-history theory suggests that the time to reach adulthood is constrained by the time needed to reach adult body size, the needing-to-learn hypothesis instead suggests that it is limited by the time needed to acquire adult-level skills.To test between these two hypotheses, we compared the development of foraging skills and growth trajectories of immature wild orangutans in two populations: at Tuanan (Pongo pygmaeus wurmbii), Borneo, and Suaq Balimbing (Pongo abelii), Sumatra. We collected behavioral data on diet repertoire, feeding rates and ranging competence during focal follows, and estimated growth through non-invasive laser photogrammetry.

Results

We found that adult-like diet repertoires are attained around the age of weaning and that female immatures increase their repertoire size faster than their male peers. Adult-level feeding rates of easy techniques are reached just after weaning, but several years later for more difficult techniques, albeit always before adulthood (i.e. age at first reproduction). Independent immatures had faster feeding rates for easy to process items than their mothers, with male immatures achieving faster feeding rates earlier in development relative to females. Sumatran immatures reach adult-level feeding rates 2–3 years later than their Bornean peers, in line with their higher dietary complexity and later weaning. The range-use competence of independently ranging and weaned immatures is similar to that of adult females. Body size measurements showed, immatures grow until female age of first reproduction.

Conclusions

In conclusion, unlike in humans, orangutan foraging skills are in place prior to reproduction. Growth trajectories suggest that energetic constraints, rather than skills, best explain the length of immaturity. However, skill competence for dietary independence is reached later where the adult niche is more complex, which is consistent with the relatively later weaning age with increasing brain size found generally in primates, and apes in particular.

     

Traditions in monkeys

Traditions, defined as relatively long‐lasting behavioral practices shared among members of a group partly via social learning, were studied in monkeys, specifically Japanese macaques, before being studied in great apes. Although apes and humans may share some social learning capacities that are absent in monkeys, a complete understanding of the roots of human culture requires attention to the socioecological conditions favoring traditions, however generated, in animals generally and in multiple behavioral domains. Using the four criteria of intergroup variation, observation of the origin and spread of a novel behavior, dissemination patterned according to age or kinship, or individuals' close observation of others' performance of the behavior before engaging in it, over twenty‐five behaviors have been nominated as traditions in free‐ranging monkey populations. Tolerant gregariousness has been proposed to increase the likelihood of the emergence of traditions in any behavioral domain. Omnivory and extractive foraging should favor the emergence of foraging‐related traditions; strong cooperative relationships and flexible coalitionary structure should favor the emergence of social conventions that function to test social bonds. These conditions are taxonomically widespread. Thus, the current restriction of most reported free‐ranging monkey traditions to two taxa (Macaca fuscata and Cebus) is likely to reflect variation in primatologists' research goals, methods, and concepts rather than real interspecific variation in the propensity to generate traditions.