Fernando Colmenares

Tubes, tables and traps: great apes solve two functionally equivalent trap tasks but show no evidence of transfer across tasks

Previous studies on tool using have shown that presenting subjects with certain modifications in the experimental setup can substantially improve their performance. However, procedural modifications (e.g. trap table task) may not only remove task constraints but also simplify the problem conceptually. The goal of this study was to design a variation of the trap-table that was functionally equivalent to the trap-tube task. In this new task, the subjects had to decide where to insert the tool and in which direction the reward should be pushed. We also administered a trap-tube task that allowed animals to push or rake the reward with the tool to compare the subjects’ performance on both tasks. We used a larger sample of subjects than in previous studies and from all the four species of great apes (Gorilla gorilla, Pan troglodytes, Pan paniscus, and Pongo pygmaeus). The results showed that apes performed better in the trap-platform task than in the trap-tube task. Subjects solved the tube task faster than in previous studies and they also preferred to rake in rather than to push the reward out. There was no correlation in the level of performance between both tasks, and no indication of interspecies differences. These data are consistent with the idea that apes may possess some specific causal knowledge of traps but may lack the ability to establish analogical relations between functional equivalent tasks.

Clans and Harems in a Colony of Hamadryas and Hybrid Baboons: Male Kinship, Familiarity and the Formation of Brother-Teams

Three features of the hamadryas society, Papio hamadryas, which are quite unique among Old World monkeys, are its multileveled structure (i.e. harems, clans, bands, troop), the reported pattern of female dispersal (i.e. males tend to remain in their natal clans whereas females tend to move between clans and bands), and the special bonds that develop between adult males. It has also been hypothesized that the males of a clan are genetically related. In this paper a causal approach is adopted in order to investigate the proximate factors which can account for the structure/dynamics of socio-spatial group organization observed over two years in a large colony of hamadryas and hybrid baboons housed in an outdoor enclosure in the Madrid Zoo, containing 18 adult males with known kin relations. I first examined the types of grouping observed in the colony and the alternative social strategies used by the different male individuals during their ontogenetic trajectories for acquiring, and maintaining, females. Since the hamadryas baboon is considered a female-transfer species, I studied whether the sex that stays, that is, the males, developed some kind of mutual affiliative relationship, as one would predict, and whether their inter-male bonding preferences were based on genetic relatedness or on familiarity (i.e. sharing the same developmental environment during socialization).

Greeting behaviour between male baboons : oestrous females, rivalry and negotiation

Among hamadryas baboons, Papio hamadryas, but not savanna baboons, P. anubis, P. cynocephalus, P. ursinus, the most frequent interaction observed among males, especially adults, in the context of rivalry over females is greeting. This paper investigates its possible functions. Interactions of greeting (asymmetrical, symmetrical and unreciprocated), aggression and coalitions observed between 20 males, members of a large multi-harem colony of baboons (hamadryas, cynocephalus and their hybrids) housed in the Madrid Zoo, were recorded. Males in possession of sexually mature females, and especially those in control of oestrous females (possessors), tended to initiate and receive symmetrical greetings, tended not to be greeted back when they initiated a greeting and not to greet back when they received a greeting, and tended to be frequent targets of coalition solicitations. Greetings were always given by possessors to rivals. It is suggested that, in the context of rivalry over females, greeting could be a strategy of negotiation whereby possessors and their rivals can assess the situation, influence each others roles in the relationship, and eventually resolve conflicts without having to fight. Qualitative evidence concerning developmental careers and contexts are also used to substantiate this interpretation. Differences between male hamadryas and savanna baboons in the use of strategies directed towards rivals and possessors in the context of competition over females are also discussed.

Relative quantity judgments in South American sea lions (Otaria flavescens)

There is accumulating evidence that a variety of species possess quantitative abilities although their cognitive substrate is still unclear. This study is the first to investigate whether sea lions (Otaria flavescens), in the absence of training, are able to assess and select the larger of two sets of quantities. In Experiment 1, the two sets of quantities were presented simultaneously as whole sets, that is, the subjects could compare them directly. In Experiment 2, the two sets of quantities were presented item-by-item, and the totality of items was never visually available at the time of choice. For each type of presentation, we analysed the effect of the ratio between quantities, the difference between quantities and the total number of items presented. The results showed that (1) sea lions can make relative quantity judgments successfully and (2) there is a predominant influence of the ratio between quantities on the subjects’ performance. The latter supports the idea that an analogue representational mechanism is responsible for sea lions’ relative quantities judgments. These findings are consistent with previous reports of relative quantities judgments in other species such as monkeys and apes and suggest that sea lions might share a similar mechanism to compare and represent quantities.

GROOMING AND COERCION IN ONE-MALE UNITS OF HAMADRYAS BABOONS: MARKET FORCES OR RELATIONSHIP CONSTRAINTS?

Summary In the stable and cohesive social groups of primates (and other group-living mammals)individuals maintain long-lasting partnerships with a subset of their group companions. Suchinter-individual relationships are based on the active exchange of a variety of af” liative,agonistic and cooperative behaviour patterns. Since these interactions in‘ uence the partners’biological ” tness they are often regarded as ‘ services’ or ‘ commodities’ that are offered(‘ sold’ ) and demanded (‘ bought’ ) by individuals in order to cultivate those partnerships thatbest contribute to maximise their ” tness. According to the biological markets theory, anindividual’ s attractiveness as a social partner depends on the value of the services that itcan provide and trade for, which depends on the levels of supply and demand, that is, a givenservice is more expensive to buy, the fewer are the individuals that offer it relative to theindividuals that demand it. This paper uses data on grooming ( i.e. investment and outbiddingcompetition), female aggression (

The role of inhibition in young children’s altruistic behaviour

By behaving altruistically, individuals voluntarily reduce their benefits in order to increase their partners’. This deviation from a self-interest-maximizing function may be cognitively demanding, though. This study investigates whether altruistic sharing in 4- to 6-year-old children, assessed by a dictator game (DG), is related to three measures of executive functioning, that is, inhibitory control, working memory, and cognitive flexibility. We found that children who turned out to be altruistic in the DG performed better on an inhibition task than non-altruists did. This finding lends support to the hypothesis that altruistic sharing might be somewhat constrained by the child’s ability to inhibit a natural tendency to preserve his or her own resources. Much research is needed to understand the role of inhibitory control in the development of costly sharing and the consolidation of inequity aversion.

Is Postconflict Affiliation in Captive Nonhuman Primates an Artifact of Captivity

Researchers have conducted most studies on primate conflict management and resolution in captive settings. The few studies on groups of the same species in captivity and in the wild and the overall comparison across species of findings from studies in both settings have reported patterns of variation in the rates of various postconflict affinitive behaviors that may be setting related. In fact, some authors have claimed that the high rates of postconflict affiliation reported in captive studies could represent an artifact of captivity. I explored the claim and conclude that it is unjustified. I argue that the dichotomy captivity vs. wild is conceptually meaningless and scientists should abandon it as an explanatory variable, that differences across studies both in setting-related variables and in the methods used for assessing postconflict affiliation reduce the strength of comparisons within and across settings, that the empirical evidence thus far available neither allows adequate assessment nor supports any claim that links the rate of postconflict affiliation to captivity or wild conditions, and that studies conducted in both settings may be equally useful—and should be used—to test theoretically relevant hypotheses regarding the causes and predictors of variation in postconflict affiliation. Instead of asking the title question, I would ask which variables influence postconflict affiliation and then whether the variables are really associated only with one of the two settings.

Postconflict Affiliation of Aggressors in Papio hamadryas

Researchers have associated variation in the occurrence of postconflict behaviors with variation in the relationship quality between involved individuals. Apart from those on the great apes, the vast majority of postconflict studies involved female-bonded species and focused on the victim. We examined postconflict affiliation involving the aggressor in a non-female-bonded species, hamadryas baboons (Papio hamadryas), and investigated the influence of relationship quality on the occurrence of 2 types of postconflict affiliative behaviors. Hamadryas baboons reconciled after a conflict and the highest rate of reconciliation was between one-male unit (OMU) leader males and their females. Via direct measures of relationship characteristics we also found that partners with higher-quality relationship, e.g., highly affiliative dyads and allies, showed higher levels of conciliatory tendency than dyads with lower-quality relationship, e.g., less affiliative dyads and non-allies. We found evidence of postconflict third-party affiliation initiated by aggressors, but not by third parties. Further, aggressor-initiated affiliation was more likely with individuals of the same OMU and individuals with which the aggressor maintained a strongly affiliative relationship. Our findings provide further support for relationship quality as a fundamental underlying factor not only in reconciliation, but also in postconflict affiliations involving third parties.

Application of hierarchical linear modelling to the study of trajectories of behavioural development

Students of behavioural development often collect andanalyse longitudinal data on a sample of individuals(Bateson 1981; Sackett et al. 1981; Chalmers 1987). Forexample, primate studies of behavioural and relationshipdevelopment have typically provided data on rates of,or percentages of time engaged in, the performance ofvarious behaviours across the individuals’ early ontogeny(e.g. Fairbanks 1996; Deputte 2000). The longitudinalrecords for each individual, collected on multiple occa-sions, are then pooled per age intervals of varying length.Commonly, such longitudinal data are analysed usingeither a mixed design analysis of variance (ANOVA) or aconventional (simple or multiple) regression analysis (Zar1999; David 2002). In this commentary, we demonstratea number of serious problems in using these methods,and describe an alternative that avoids them.Researchers applying mixed design ANOVA to thestudy of behavioural development typically use age of theindividual (i.e. time blocks) as the within-subject factor,and variables such as sex or species as the between-subjects factors (e.g. Maestripieri 1994; Suomi et al. 1996).Although ANOVA models can be used to analyse longitu-dinal data they have two major limitations. First, theyrequire a balanced data collection design, with the samenumber of individuals per measurement occasion and thesame interval between consecutive measurements. Whenthese requirements are not fulfilled, which is often thecase in observational studies of spontaneously occurringsocial interactions, a number of complications arise(e.g. Hox & Kreft 1994). Second, ANOVA models assumehomogeneous (co)variances at level 1, that is, a constantwithin-subject covariance structure (Zar 1999; David2002). This assumption is often not met by developmen-tal data, resulting in a Type I error greater than thespecified .Animal behaviour researchers using traditional regres-sion analysis have used two major approaches. The firsttreats all predictor or independent variables, such as ageof infant, sex, cohort, maternal experience or dominancerank, as if they pertained to a single level (e.g. Bramblett& Coelho 1985; Altmann & Samuels 1992) and theircontributions to the observed variance in the rate ofbehaviour during the whole study period are thenassessed. The second regression modelling approachis known as the intercepts-and-slopes-as-outcomesapproach (e.g. Bryk & Raudenbush 1992; Hox & Kreft1994). In this case, two separate steps are taken. First,linear (or curvilinear) regressions are fitted to thedevelopmental functions for each subject. Next, theparameters from these regression equations are usedas dependent variables in subsequent analyses to bepredicted by one or a set of independent variables(e.g. Wasser & Wasser 1995).The application of simple or multiple, single-levellinear regression to the analysis of longitudinal data isinadequate for several reasons (Bryk & Raudenbush 1992;Hox & Kreft 1994; Goldstein et al. 1998; van der Leeden1998; Snijders & Bosker 1999). First, this approach isconceptually unsound because it ignores the hierarchicalnature of longitudinal data in which observations withinindividuals are dependent. Second, conventional single-level methods disaggregate all higher level explanatoryvariables to the lowest level, followed by an ordinary leastsquares (OLS) regression analysis. Therefore, they do notprovide methods to test for the effect of independentvariables on the variation observed in the parameters ofchange (initial status, rate of development, and soon), which is one of the major theoretical concerns ofthose interested in the study of behavioural develop-ment. When OLS is applied to longitudinal data, theassumption of independence of residual error terms isviolated and this leads to inefficient estimates and a TypeI error rate that is much higher than the nominal level(Hox & Kreft 1994; van der Leeden 1998).In the intercepts-and-slopes-as-outcomes approach,separate fixed-effects regression models are first fittedwithin each individual, using level 1 explanatory vari-ables as predictors. Next, the within-individual growthcoefficients are, in turn, used as dependent variables to bepredicted by level 2 explanatory variables (Wasser &

Male takeovers are reproductively costly to females in hamadryas baboons: a test of the sexual coercion hypothesis.

During male takeovers, in addition to fighting off the female’s current mating partner, males may exhibit intense aggressive mate guarding of the newly acquired females. Recent studies indicate that coercive sexual aggression by males is an important strategy through which sexual conflict is expressed. Previous tests of the sexual coercion hypothesis in primates have focused on assessing if female mate choice is effectively reduced by male aggression, however, only one recent study has tested a critical prediction of this hypothesis, namely, that male coercion is reproductively costly to victim females. The present study uses 15 years of data on inter-birth intervals from a large multilevel colony of baboons, mostly Papio h. hamadryas, with a mating system based on harem-defence polygyny to examine if male takeovers impact the length of the abducted females’ inter-birth intervals. Our analysis of 121 inter-birth intervals from 45 adult females indicates that male takeovers are reproductively costly to abducted females as they are associated with an increase in the time they take to conceive and a lengthening of the inter-birth intervals. We discuss how several factors may contribute to this reproductive cost, including male-female sexual conflict, male-male competition, and female-female competition. Our findings suggest that the male’s aggressive herding is the main contributor to the abducted females’ immediate reproductive cost. We argue that although some of the male’s aggressive herding may be driven by male-male competition, nonetheless, it serves a coercive function as it both constrains the female’s mate choice options and hampers her immediate breeding performance. This conclusion is backed up by results obtained in the only other study that has tested the same prediction and which has been carried out in a wild population of hamadryas baboons.