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. Author manuscript; available in PMC: 2014 Jul 22.
Published in final edited form as: J Comp Psychol. 2013 Sep 23;128(2):215–223. doi: 10.1037/a0034420

Public Information Use in Chimpanzees (Pan troglodytes) and Children (Homo sapiens)

Gill L Vale 1, Emma G Flynn 2, Susan P Lambeth 3, Steven J Schapiro 4, Rachel L Kendal 5
PMCID: PMC4106426  NIHMSID: NIHMS604714  PMID: 24060244

Abstract

The discernment of resource quality is pertinent to many daily decisions faced by animals. Public information is a critical information source that promotes quality assessments, attained by monitoring others’ performance. Here we provide the first evidence, to our knowledge, that chimpanzees (Pan troglodytes) use public information to guide resource selection. Thirty-two chimpanzees were presented with two simultaneous video demonstrations depicting a conspecific acquiring resources at a fast (resource-rich) or slow (resource-poor) rate. Subsequently, subjects selected the resource-rich site above chance expectation. As a comparison, we report evidence of public information use in young children. Investigation of public information use in primates is pertinent, as it can enhance foraging success and potentially facilitate payoff-biased social learning.

Keywords: public information, social information, social learning, social cognition

Social learning denotes behavior or learning that is altered according to other organisms’ presence, behavior, or behavioral products (Heyes, 1994). A large body of evidence indicates that many animal species are capable of social learning (Brown & Laland, 2003; Galef & Giraldeau, 2001; Reader & Biro, 2010; Reader & Laland, 2002), culminating in regional variation in behavior, suggestive of tradition or culture (Perry, 2011; van Schaik et al., 2003; Whiten et al., 1999). Wild chimpanzees, in particular, display one of the broadest cultural repertoires recorded, with geographical variation in food extraction and processing methods, as well as social behavior, thought to be underpinned by social learning rather than genetic or ecological factors alone (Whiten et al., 1999). Ancillary studies of captive chimpanzees support claims that social learning plays a role in regional behavioral variation in the wild (Horner, Proctor, Bonnie, Whiten, & de Waal, 2010; Whiten, Horner, & de Waal, 2005; Whiten et al., 2007). Indeed, both arbitrary behavioral traditions (Bonnie, Horner, Whiten, & de Waal, 2007) and foraging traditions (Horner, Whiten, Flynn, & de Waal, 2006) have been shown to emerge through social learning in this species.

A trend exists in the social learning literature to document how chimpanzees socially acquire foraging techniques (Hopper et al., 2007; Horner & Whiten, 2005) and, more recently, from whom they learn (Horner et al., 2010). In particular, focus has been given to the question of whether chimpanzees imitate (broadly defined as the copying of behavioral actions) or rely on other social learning processes (Hopper, Lambeth, Schapiro, & Whiten, 2008; Tennie, Call, & Tomasello, 2006), a question that remains a topic of debate (Tennie, Call, & Tomasello, 2009; Tennie, Call, & Tomasello, 2012). In addition, work on model-based, biased social learning has begun to document selective copying regarding to whom it is that chimpanzees attend and from whom they copy. Chimpanzees, for example, have been shown to preferentially copy dominant over low-ranking conspecifics, and selectively attend to the food-associated behavior of older or same-aged individuals (Biro et al., 2003; Horner et al., 2010; Kendal et al., 2013).

One area of interest that has received relatively little attention addresses whether social information influences chimpanzees’ decisions of where to forage and, in particular, whether the foraging successes of others act as cues to locating the most abundant food resources. When animals feed, they produce information, often inadvertently, through their performance, activities, and decisions, as well as in their by-products. This information can then be used by others as cues to resource locations (Danchin, Giraldeau, Valone, & Wagner, 2004). Theoretical modeling suggests that social learning (resulting in joining feeding conspecifics) outcompetes individual sampling in changing environments in which resources with high payoffs are associated with a high probability of samplers failing to find food (Arbilly, Motro, Feldman, & Lotem, 2011). Thus, for species that experience a variable food supply from which nutritional sources might be devoid, (e.g., seasonal fruits, Basabose, 2004; Watts, Potts, Lwanga, & Mitani, 2012), attending to foraging conspecifics may prove an adaptive strategy. Although the question of whether graded foraging performances cue resource quality judgments in primates remains understudied, evidence of the capacity to source and use social information to locate food resources has been documented in various primate species. The presence of a conspecific at one of two opaque food containers (local enhancement), for instance, can act as a social cue used by chimpanzees to locate a container baited with food (Itakura, Agnetta, Hare, & Tomasello, 1999). In a similar way, Tonkean macaques (Macaca tonkeana) have been shown to use both olfactory and visual residual signs, produced as a by-product of conspecific feeding, to locate distant food sources of the same type (Drapier, Chauvin, & Thierry, 2002).

Social cue use has been documented in all four great ape species (Pan troglodytes, Pan paniscus, Gorilla gorilla gorilla and Pongo pygmaeus abelii; Buttelmann, Call, & Tomasello, 2008). Specifically, various behavioral cues consistent with attempts to extract hidden food from one of two locations were used by subjects to infer the location of the hidden food sources. For example, a preference was displayed for baited containers, which the experimenter smelled and attempted to bite open, compared with those that were only smelled. It is of interest to note, Buttelmann and colleagues (2008) found that when subjects possessed personal knowledge of the absence of food in both containers, they selected at random, despite differential behavioral cues performed on the containers. Thus, social information use was dependent on subjects’ own knowledge states (i.e., personal information) and when personal and social information conflicted, a preference was displayed for the reliable, personal information; a “copy [only] when uncertain” strategy (Kendal, Coolen, & Laland, 2009; Kendal, Coolen, van Bergen, & Laland, 2005). More recently, chimpanzees have been shown to remember (inaccessible) locations at which they observed a human hide food items, and when eliciting the aid of a human to gain the hidden food items, they directed them first to items of high quality (Sayers & Menzel, 2012). Thus, the chimpanzees were able to store and use both personal information regarding resource quality and social information regarding the location of resources following a delay. What is novel about the current study is an investigation of whether chimpanzees use social cues to assess resource quality (public information sensu; Valone, 1989) and use this to guide their choices of resource locations.

Although studies have shown that primate species use social cues to locate hidden food (Buttelmann et al., 2008; Itakura et al., 1999), and that feeding conspecifics can socially facilitate other animals food consumption (Visalberghi & Addessi, 2000), little is known regarding whether primates are capable of discerning food abundance based on conspecifics’ foraging successes. One of the main daily decisions facing foragers is, of course, how to optimize energetic returns. When social information acts as a cue to resource quality it is termed “public information” (Valone, 1989). Public information, specifically, is a term derived from behavioral ecology, that, rather than referring to any information that is public (available to others), is confined to social information sourced from others’ performances conveying cues regarding quality (Valone, 1989; Valone, 2007; Valone & Templeton, 2002). This can include cues to abundant resources, successful breeding partners, habitats and breeding sites, and the quality of potential competitors (Valone, 2007). Public information use does not necessitate complex social learning processes; it can occur via local enhancement (Webster & Laland, 2012), feeding rate (Coolen, Bergen, Day, & Laland, 2003) and food-related collective commotion (Laidre, 2013).

Public information use has been assessed in the common marmoset (Callithrix jacchus; Voelkl & Huber, 2007). Marmoset pairs (demonstrator– observer) were presented with four pairs of opaque containers filled with wood chips, some of which were baited with food. The marmosets could forage simultaneously, with visual access to each other, but were separated by wire mesh. Equally, paired containers were positioned adjacent to one another but separated by mesh, so that resource sites matched for the marmoset pairs. The “demonstrator” marmoset was informed of food locations and thus, the “observer” marmoset could maximize its foraging success by synchronizing its search for food with that of the demonstrator. Contrary to expectation, however, the availability of this social information did not enhance foraging success.

In chimpanzees, auditory information can signal resource quality. Chimpanzees, upon locating food, produce rough-grunt vocalizations that differ according to the producer’s food preferences (Slocombe & Zuberbühler, 2006), offering important resourcequality information. Slocombe and Zuberbühler (2005) showed that a chimpanzee altered his foraging strategy according to playbacks of a high- versus low-quality food response, suggesting that rough grunts served as a social signal to resource quality. Overall, food-searching behavior was found to be prolonged and more thorough upon hearing rough grunts produced in response to high-quality food. Food searching, in addition, tended to be longer at those resource sites associated with the rough grunt played. Thus, rough grunts may constitute an important source of auditory public information.

In Experiment 1, we aimed to examine whether chimpanzees use visual public information— differential foraging behavior of a conspecific—to identify the most abundant food source in the absence of vocal signals. Public information is predicted to be widespread in nature, promoting greater accuracy in environmental assessments (Valone & Templeton, 2002). Yet, research into public information use has largely been confined to species of birds and fish (Valone, 2007). The study of public information in chimpanzees is vital for understanding which social information contributes to the daily decisions made by this species, including whether public information facilitates resource maximization. Public information use was recently reported in chimpanzees (Martin, Biro, & Matsuzawa, 2011); observers used models’ behavioral actions to solve a matching-to-sample task. However, as the copying of behavioral decisions was not confined to resource quality (as required for the strict use of public information sensu Valone, 1989) to date, whether chimpanzees discern patch profitability by monitoring the relative success of conspecifics is unknown.

We employed a variant of Coolen, Bergen’s et al. (2003) methodology to examine whether chimpanzees use graded information to assist them in their own foraging decisions, of conspecific foraging at food-rich and food-poor sites. Simultaneous videos of a conspecific acquiring resources at two locations, each differing in terms of the rate at which food was gained (food-rich vs. food-poor), were presented. Subsequently, observer chimpanzees were given access to the resource sites, and their selections recorded. Employing video-based social stimuli with chimpanzees (Hopper, Lambeth, & Schapiro, 2012) offers the advantage of presenting the same unfamiliar model at each foraging site, thus controlling for any model-based biases (Rendell et al., 2011). This is important, due to the established influence of social dynamics, age, and perhaps previous track record of success (Biro et al., 2003; Horner et al., 2010; Kendal et al., 2013), to whom it is that chimpanzees attend and from whom they learn. As bird and fish species use public information (Valone, 2007), and given chimpanzees’ sensitivity to behavioral cues in foraging situations, their discerning auditory food signals (Slocombe & Zuberbühler, 2005), and their ability to engage in observational learning (Martin et al., 2011), we predicted that chimpanzees would display the ability to use public information.

We were additionally interested in the ability of 5-year-old children (Homo sapiens) to use public information, as, to our knowledge, whether children use public information to discern reward quality has yet to be empirically investigated. In Experiment 2, we replicated the chimpanzee study with 5-year old children (Homo sapiens) using a similar methodology. This follows previous studies that have focused on the sociocognitive skills of both chimpanzees and children, finding that young children constitute an appropriate group with which chimpanzees can be compared (Dean, Kendal, Schapiro, Thierry, & Laland, 2012; Herrmann, Call, Hernández-Lloreda, Hare, & Tomasello, 2007; Horner & Whiten, 2005). Similar to chimpanzees, the feeding behavior of children shows susceptibility to social context. Children’s food preferences, for example, have been shown to alter in accordance with peer preferences (Birch, 1980a). Children’s food intake and preferences have also been documented to positively correlate with those of parents and other adults of the same subculture (Birch, 1980b; Orlet Fisher, Mitchell, Wright, & Birch, 2002), and the amount of food consumed has been shown to vary according to one’s own size and social partner size (Salvy, Romero, Paluch, & Epstein, 2007). Given the social influence on feeding behavior and that children readily respond to social information (Lyons, Damrosch, Lin, Macris, & Keil, 2011; Wood, Kendal, & Flynn, 2012), we predicted that children would use public information as a cue to resource quality.

Experiment 1: Chimpanzees

The purpose of this experiment was to establish whether individual chimpanzees would assess resource quality by monitoring the relative foraging success of a conspecific feeding at different rates (public information use).

Method

Subjects

Thirty-nine chimpanzees participated; three were discounted, as they did not interact with the resource boxes during a pretesting phase (see Procedure) and four were discounted due to inattention to the demonstrations. The remaining 32 chimpanzees (16 male) ranged in age from 15 to 44 years (M = 30). Following previous studies, a dominant, female (Hopper, Schapiro, Lambeth, & Brosnan, 2011) unfamiliar chimpanzee served as the demonstrator. Subjects were housed at the Michale E. Keeling Center for Comparative Medicine and Research (KCCMR) facility in Bastrop, Texas. The KCCMR is fully accredited by the Association for Assessment and Accreditation of Laboratory Animal Care International. The chimpanzees were group-housed with access to enriched indoor and outdoor enclosures with climbing facilities. Subjects had participated in previous video social learning tasks (Hopper et al., 2012) and had past exposure to video for enrichment. No food or water deprivation was used during this study, which was approved by the Life Sciences Ethical Review Committee, Durham University, Durham, England, and the Institutional Animal Care and Use Committee of The University of Texas M. D. Anderson Cancer Center.

Video stimuli

Video demonstrations showed a model acquiring rewards (peanuts) at different rates (rich: approximately every 12 s, poor: approximately every 84 s; see Figure 1) from two boxes (21.5 H × 10W × 30 L cm). To achieve this, each box had a small hole situated at the back through which the food items were dispensed by the experimenter. The demonstrator could then retrieve the food items by reaching inside an opening at the front of the box. Thus, the peanuts themselves were barely visible, but the foraging/eating actions of the demonstrator were. The two boxes, resource-rich and resource-poor, were colored either yellow or black. To allow counterbalancing of the box color constituting the rich resource sites during the test sessions, four video demonstrations were captured (yellow-rich; black-poor; black-rich; yellow-poor, with the same demonstrator used in all demonstrations). To ensure that the demonstrator sourced individual peanuts at the predetermined rates, where appropriate video demonstrations were edited slightly using Picture Motion Browser (Sony) and Windows Live Movie Maker. Video editing consisted of cutting and/or looping subsections of the demonstrations. All recordings were captured with a Sony Handycam.

Figure 1.

Figure 1

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Model retrieving rewards from the resource boxes (video-demonstration stills).

Design and procedure: Pretests

As neophobic reactions to novel objects can occur in chimpanzees, a habituation stage was performed to expose subjects to the resource boxes prior to running the experiment. Chimpanzees were given sequential, color-counterbalanced exposure to the baited resource boxes. Chimpanzees that did not retrieve a grape from both boxes during this session (N = 3) were eliminated from the study. This pretest identified subjects who lacked the motivation to participate and/or those who would fail to select a resource box in test sessions due to neophobic responses to the apparatus.

Color preference was assessed using a dichotomous preference paradigm (Hopper et al., 2011). In 10 successive, counterbalanced and unrewarded trials, the experimenter simultaneously held one cylindrical token (yellow/black) in each hand and chimpanzees selected one via gesture. No color preferences were observed (yellow token selections from 10 trials M = 4.81, SD = .90; binomials, all p > .05, N = 36).

Design and procedure: Experimental test

Chimpanzees were tested individually and voluntarily within their indoor compartments (circa 2.4 × 2.4 × 1.8 m3). Demonstrations were presented on two computer monitors (48.26 cm) on separate trolleys (85 H × 51 W × 51 L cm) located adjacent to one another (separated by roughly 40 cm). The two opaque boxes (yellow/black), from which the demonstrator retrieved resources, were positioned in front of the trolleys behind an occluding barrier, and positioned (left/right) to match the box color depicted in the corresponding video. The color (yellow/black) constituting the resource-rich patch and the side (left/right) presented were counterbalanced. All subjects received one trial only. Test sessions were video recorded.

Following the demonstrations, the resource boxes were simultaneously revealed by removal of the occluding barrier and pushed toward the subjects. The resource boxes were designed such that the observers could not see the food rewards inside until they had placed their hand inside the hole at the front. Resource selection was defined as the first resource box the subjects touched. The unselected box was then removed by the experimenter to prevent chimpanzees from gaining rewards from both boxes. Upon box selection, chimpanzees could retrieve the food item from their chosen box. To reduce food intake, and since only one trial was conducted with each subject, resource boxes were each baited with one banana piece only, irrespective of box quality. This also prevented potential olfactory cues arising from a large amount of food placed in one box only. Subjects were allocated up to 2 min to make their selection, after which the trial would be terminated and the subject discounted. In practice, all selections were made in less than 13 s and no individuals were discounted. Subjects’ attention (head orientation) to the videos was noted at 10-s intervals, and those (N = 4) not meeting a criterion of attention at ≥6 10-s intervals, were discounted.

Design and procedure: Statistical analysis

Due to the small sample size and dichotomous dependent variable, nonparametric statistics were used. First we investigated whether the number of resource-rich selections differed from chance (50%) using the binomial test. Mann–Whitney U tests were conducted to ascertain whether subject age, latency to box selection, and attention levels differed according to resource selection (rich/poor). Whether resource selection differed according to sex, the video sets viewed (yellow-rich/black-rich), or the sequential order of box presentation during the pretest habituation phase, was assessed using chi-square and Fisher’s exact (i.e., where contingency tables contained expected values of below five) tests. In addition, binomial tests were used to assess side and color biases in resource selections (chance = 50%).

Results

As predicted, the majority of (22 of the 32) chimpanzees selected the resource-rich box following presentation of the demonstrations (binomial, p = .03, one-tailed, 95% CI [.53, .84]; see Figure 2). The mean time taken to select a resource box was 4 s (SD = 3). No significant differences were observed between age, U = 74.50, N = 32, p = .15, sex, χ2(1) = 2.33, p = .25, latency to selection, U = 94.50, N = 32, p = .54, or attendance, U = 95.50, N = 32, p = .57, as a function of the resource box selected.

Figure 2.

Figure 2

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Resource-rich and resource-poor selections (%) per species. Dotted line represents chance level, * = p < .05.

There was no significant difference in resource-box selection following the demonstration as a function of the box presented first during the box exposure pretest, χ2(1, 32) = 2.32, p = .25. Resource-box selections did not differ according to the different video sets needed to counterbalance color and resource richness (Fisher’s exact test: N = 32, p = 1. 00). Moreover, the chimpanzees displayed no side bias (binomial: N = 32, p = .38, left N = 13 and right N = 19) nor color bias (binomial: N = 32, p = .86, black N = 15 and yellow N = 17).

Experiment 2: Children

Experiment 1 showed that chimpanzees discerned resource quality from video demonstrations. We now turn to the question of whether children use public information to assess resource quality. The child study methodology was identical to the chimpanzee study except for changes, detailed below, to accommodate species differences.

Participants

Thirty-six 5-year-old children (17 male) were recruited from three primary schools in the North East of England. An individual girl, unfamiliar to the participants (aged 5 years), acted as the demonstrator via video for all children.

Video Stimuli

Video presentations were shorter in duration (1 min 40 s) than for the chimpanzees and, due to retention of the overall resource quantities presented (rich 15 vs. poor 3), the rate at which each reward was dispensed at the resource-rich location was increased (from every 12 to every 6 s; see Table 1). Stickers constituted the resource due to the ethical considerations of provisioning consumables. The boxes consisted of two opaque, hemisphere-shaped plastic containers (total surface area 763.41 cm2). As children displayed color preferences (Boyatzis & Varghese, 1994), the boxes were differentiated by pattern (large or small black squares). Upon retrieving stickers, the demonstrator placed them in an opaque cup. This prevented a stack of stickers from accumulating, which could have served as an additional cue for the children, relative to chimpanzees, in whose case rewards were immediately consumed by the demonstrator.

Table 1.

Time (Minutes, Seconds) at Which Single Rewards Were Dispensed During Demonstrations

Pan Homo
Resource-rich Resource-poor Resource-rich Resource-poor
0.05 0.05 0.06 0.06
0.17 0.12
0.29 0.18
0.41 0.24
0.53 0.30
1.05 0.36
1.17 0.42
1.29 1.29 0.48 0.48
1.41 0.54
1.53 1.00
2.05 1.06
2.17 1.12
2.29 1.18
2.41 1.24
2.53 2.53 1.30 1.30
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Design and Procedure

Testing was conducted in a quiet room at each child’s school away from the rest of their class. Each child participated in one trial only. Participants were told by an experimenter (G. V.), “I would like you to watch videos of a girl getting stickers, and then after the videos you will get a chance to find stickers” and given verbal prompts (“are you watching the videos?” “can you see what the little girl is doing?”) if attention lapsed. It is noteworthy that the children were encouraged to attend to the videos by experimenter prompting, with no verbal prompts given to the chimpanzees. Following the videos, the occluding barrier was removed to reveal the resource boxes and children were instructed, “You can have a look in the boxes now.” Participants were allocated up to 1 min to make a resource selection, defined as the first box touched or gestured toward. The chosen box was then opened to retrieve the stickers. The number of baited stickers in the resource-rich and resource-poor boxes matched the number obtained by the demonstrator in the corresponding videos (15 and 3, respectively). As the data were derived from one trial only, the number of stickers gained did not influence the study results.

Results

As predicted, 24 of 36 children selected the resource-rich location, which is above that predicted by chance alone (binomial test: p = .03, one-tailed, 95% CI [.51, .82] see Figure 2). Average time to box selection was 6 s (SD = 5). Resource selection was not related to sex, χ2(1) = .22, p = .73, or box selection latency (U = 95.50, N = 36, p = .10). No side (binomial test; N = 36, p = .24) or box pattern preferences (binomial test; N = 36, p = .62) were observed. There was no significant difference in the species’ tendencies to choose the “rich” patch, χ2(1) = .03, p = 1.00.

Discussion

Chimpanzees (Pan troglodytes) and children (Homo sapiens) are capable of social learning (Horner et al., 2006). Numerous studies have documented that group-specific traditions occur in these species through differential copying of knowledgeable conspecifics (Flynn & Whiten, 2008; Whiten et al., 2005; Whiten et al., 2007). Such studies have tended to concentrate on the copying of behavioral methods, often using tools, of gaining a food reward that exhibits (novel) food-extractive behavior. Less is known about whether social information relating to differential food abundance guides primates’ subsequent foraging decisions. The ability to discriminate between resource qualities using public information allows profitable food sources to be identified and visited with potentially greater accuracy than if using personal information alone (Arbilly et al., 2011; Valone, 2007). Our results indicate that chimpanzees and 5-year-old children possess this ability, interestingly showing high concordance in public information use across species. Thus, in addition to attending to social cues to locate food sources (Buttelmann et al., 2008; Itakura et al., 1999), chimpanzees and children were able to select reward sources according to the graded acquisition (of food/stickers) performance of a conspecific. Children and chimpanzees thus performed at comparable levels despite methodological differences, which included verbal attention prompts for children but not chimpanzees, and the provisioning of stickers rather than consumables.

Foraging decisions rely on various cognitive skills. Route planning, cognitive maps, memory of food sources, travel time, competition for food and likelihood of patch depletion can all influence decisions of where to forage (Noser & Byrne, 2010). Much of this information is derived from personal experience; however, social foragers are afforded an additional information source derived from others’ activities (Dall, Giraldeau, Olsson, McNamara, & Stephens, 2005). Our results suggest that public information sourced from conspecific foraging success may, in addition to personal information (Beran, Evans, & Harris, 2008) and auditory signals (Slocombe & Zuberbühler, 2006), aid in locating quality resources in chimpanzees and hence constitute one more factor among many that could contribute to foraging decisions

The use of public information has many implications. Primates may optimize foraging efficiency through exploiting inadvertent social information manifested in the foraging activity of conspecifics (Arbilly et al., 2011). In the present study, the relative number of times or the rate at which the demonstrator reached inside each resource box to acquire reward items, and the subsequent consumption activity for chimpanzees, could constitute potential cues by which resource quality was determined. Future investigation would benefit from control conditions to isolate the cues utilized to discern resource abundance. The inclusion of consumption only and reward retrieval without consumption would prove beneficial conditions in this regard.

Public information use can allow patch estimation to occur without engaging in personal sampling (Coolen et al., 2003). Public information may therefore aid decisions of food approach through an assessment of whether food sources will support additional foragers without direct food contest. That is, use of public information could benefit foragers through conflict avoidance by allowing a predetermination of whether approach would likely result in conflict due to low-resource abundance versus safer approach to more abundant nonmonopolizable food sources. When public information is derived from successful dominant foragers, an ability to use it following the departure of that individual may prove beneficial for subordinate observers (McQuoid & Galef, 1992). Chimpanzees have been shown to remember, following a delay, locations they previously saw a human hide food and to “direct” a human helper to hidden food of high quality first (Sayers & Menzel, 2012). This, along with other numerous studies, show that chimpanzees are capable of delayed social information use (Bering, Bjorklund, & Ragan, 2000; Bjorklund, Yunger, Bering, & Ragan, 2002). It is worth noting, however, that where food is markedly limited, public information will be of little value, even after a delay, because due to depletion, food consumption depends upon who discovers it first (Giraldeau, Valone, & Templeton, 2002). In this context, reliance upon personal information would best serve the forager. Thus considerations of public and personal information use are pertinent to chimpanzees, a species in which fission–fusion dynamics are pronounced, as they allow assessment of resource distribution and abundance, factors that can underwrite party size (Aureli et al., 2008).

Public information has the potential to aid foraging activity through signaling patch depletion (Fraser, Ruxton, & Broom, 2006; Templeton & Giraldeau, 1995). It is of interest that chimpanzees and children selected the resource box associated with the demonstrator retrieving rewards at the fastest rate. This suggests that the faster feeding rates did not signal patch depletion. Because increased feeding rate can mark rapid food depletion, sustained high rates should signal food abundance and slower (or reducing) rates should indicate limited food supply. Finding that chimpanzees and children displayed a preference for the resource supporting rapid food retrieval is in line with reports that species are attracted to food sites at which the feeding rate is faster (Coolen et al., 2003; Coolen, Ward, Hart, & Laland, 2005). To investigate whether public information provides cues to patch depletion, it would be of interest to examine the influence of demonstrator-foraging success, varying success (x retrieval attempts with no food obtained) and the feeding rate (gradual reduction vs. increased rate of food obtained) in addition to utilizing real-time demonstrations.

Although chimpanzees in this study displayed a preference for the rich resource box, it remains unclear whether this finding would hold in a group context. Video footage of a foraging demonstrator, theoretically, could have alleviated any competitive foraging demands that would otherwise occur in more naturalistic group settings, including dominance factors (Emery Thompson, Muller, Kahlenberg, & Wrangham, 2010; Muller & Wrangham, 2004; Sapolsky, 1992). This scenario is beneficial for the establishment of whether chimpanzees can use public information, but nevertheless does not allow an assessment of whether they do use public information more generally in the wild (Boesch, 2007, 2008). In groups, factors such as the dominance rank of those already foraging, the number of foragers, food distribution (monopolizable or not) and species level foraging strategies (e.g., contest and/or scramble competition) will likely play a prominent role in foraging decisions (Murray, Eberly, & Pusey, 2006; Murray, Mane, & Pusey, 2007).

Moreover, in chimpanzees, foraging strategies also differ according to sex and reproductive status. Lactating females tend to visit fewer of the available high-value resources per day than do sexually receptive females and males, but stay at resource locations longer (Bates & Byrne, 2009). Males, in contrast, have been shown to use linear daily foraging paths, indicative of a strategy of combining foraging needs with territorial defense (Bates & Byrne, 2009). Accordingly, although chimpanzees in this study showed public information use, individual foraging strategies employed in the wild, including patch departures, are mediated by optimizing food intake, and other factors such as sex-specific needs. Thus, foraging decisions in this species represents a complex process that may not only rely on personal and public information, but one that is also variable according to individual needs.

To understand decision making in chimpanzees (and children) it is important to determine the information sources underpinning behavioral actions. In this study we demonstrated that public information derived from differential foraging success can influence subsequent foraging decisions. How human and nonhuman primates weigh personal and public information, especially when they conflict (Kendal et al., 2005), and how social dynamics (Coussi-Korbel & Fragaszy, 1995), such as dominance rank, influence public information use, represent further important questions. Moreover, the pertinence of public information, especially in species-displaying traditions (Laland & Galef, 2009), lies in its use enabling payoff assessments of resources without participating in personal sampling, which can be costly in terms time and energy losses (Valone, 2007). To this end, public information has the potential to facilitate informed payoff-biased copying decisions, whereby individuals adopt behaviors in proportion to their profitability. One aspect of import to cumulative culture, in which cultural traits and behaviors become more complex and efficient across generations such that a single individual could never invent the trait within its lifetime (Tennie et al., 2009), is recognizing when a behavioral option is a beneficial modification that should be incorporated into the existing cultural trait (Laland, 2004). Public information may promote rudimentary “copy if better strategies” (Schlag, 1998, 1999), allowing the “ratcheting up” (Tennie et al., 2009) of cultural traits (e.g., technology) over generations. If quality assessments—made through monitoring the relative payoffs gained by conspecifics, or one’s self, using different traits— encourage the social acquisition of beneficial trait modifications (e.g., food-processing techniques), these could have potential consequences for cultural evolution. Specifically, it is possible that cumulative culture, which is widely held to be responsible for humanity’s success (Kendal, Rendell, Pike, & Laland, 2009), depends upon use of payoff-biased social learning strategies. Whether public information use may promote selectivity in what is copied through facilitating such payoff-biased social learning, and whether use of such cultural transmission biases (Rendell et al., 2011) is instrumental in the observed cross-species distribution of cumulative culture (Dean et al., 2012), requires further investigation.

Acknowledgment

G. L. V. was funded by a Durham University health and social science interdisciplinary studentship. R. L. K was funded by a Royal Society Dorothy Hodgkin Fellowship, and R. L. K and E. G. F were supported by a Durham University Seedcorn Fund. S. J. S and S. P. L were supported by the United States Department of Health and Human Services, National Institutes of Health Grant NIH RR-15090. We thank Hartside Primary, Stanley Crook Primary, and Leadgate Infant and Nursery schools, Alina Kendal (demonstrator), staff at the Michale E. Keeling Center for Comparative Medicine and Research and Lydia Hopper for logistical support. We are grateful for the helpful comments of two reviewers, Richard Moore and Irene Pepperberg.

Contributor Information

Gill L. Vale, Centre for Coevolution of Biology & Culture, Department of Anthropology & Department of Psychology, Durham University, Durham, England

Emma G. Flynn, Department of Psychology, Durham University

Susan P. Lambeth, Department of Veterinary Sciences, The University of Texas M. D. Anderson Cancer Center

Steven J. Schapiro, Department of Veterinary Sciences, The University of Texas M. D. Anderson Cancer Center

Rachel L. Kendal, Department of Anthropology, Centre for Coevolution of Biology & Culture, Durham University

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