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Open Access Publications from the University of California


The International Journal of Comparative Psychology is sponsored by the International Society for Comparative Psychology. It is a peer-reviewed open-access digital journal that publishes studies on the evolution and development of behavior in all animal species. It accepts research articles and reviews, letters and audiovisual submissions.

Volume 26, Issue 4, 2013

Issue cover

Research Article

Chorus Song of the Indri ( Indri indri : Primates, Lemuridae): Group Differences and Analysis of Within-group Vocal Interactions

The loud chorus songs of the group-living lemur Indri indri are a striking feature of rainforest areas of eastern Madagascar. Despite some research on the conspicuous vocal display of the indri, two hypotheses have not been addressed: do groups differ in the acoustic properties of their songs, and is there evidence of coordinated singing between individuals within groups. We recorded and analyzed the songs of three indri groups to examine these two questions. To answer the first question, we made quantitative spectral measures on songs of the three groups and performed multivariate analyses of the acoustic features of the notes constituting the songs. Our results showed songs of the three groups differed significantly, although there was overlap between groups. To answer the second question, we classified note types and quantified their occurrence as overlapping and abutting pairs. We found non-random associations between sequential note types in all three indri groups. These associations were consistent among groups, suggesting that individuals follow consistent answering rules when contributing to choruses. Whether indris use acoustic group identifiers in management of behavioral strategies and how within-group coordinated note production might function remain unknown. We compare our results to a number of taxonomically diverse species that live in groups and broadcast chorus and duet vocal signals.

Capuchin Monkeys Exercise Self-control by Choosing Token Exchange Over an Immediate Reward

Self-control is a prerequisite for complex cognitive processes such as cooperation and planning. As such, comparative studies of self-control may help elucidate the evolutionary origin of these capacities. A variety of methods have been developed to test for self-control in non-human primates that include some variation of foregoing an immediate reward in order to gain a more favorable reward. We used a token exchange paradigm to test for self-control in capuchin monkeys ( Cebus apella ). Animals were trained that particular tokens could be exchanged for food items worth different values. To test for self-control, a monkey was provided with a token that was associated with a lower-value food. When the monkey exchanged the token, the experimenter provided the monkey with a choice between the lower-value food item associated with the token or another token that was associated with a higher-value food. If the monkey chose the token, they could then exchange it for the higher-value food. Of seven monkeys trained to exchange tokens, five demonstrated that they attributed value to the tokens by differentially selecting tokens for higher-value foods over tokens for lower-value foods. When provided with a choice between a food item or a token for a higher-value food, two monkeys selected the token significantly more than expected by chance. The ability of capuchin monkeys to forego an immediate food reward and select a token that could then be traded for a more preferred food demonstrated some degree of self-control. Thus, results suggest a token exchange paradigm could be a successful technique for assessing self-control in this New World species.

The Use of a Five Factor Model in Equine Personality Research

In order to test the validity of a Five Factor Model of personality on horses, a questionnaire was replicated from a previous study, with an added option of don’t know to the traditional 5-point Likert scale. Raters responded to seventeen items of the 60-item scale with don’t know responses greater than 10% of the time and these seventeen items were subsequently removed from the study. A Principal Components Analysis was used with the remaining items, resulting in eight factors: Neuroticism, Active, Conscientiousness, Agreeableness, Openness, Social Extraversion, Temperamental, and Disciplined. These components correspond well to the five components extracted in the original study, indicating good reliability of the scale. However, 17 items from the original questionnaire were deemed irrelevant by raters, indicating a threat to validity. Though the remaining items were able to be used in analyses, further studies should examine if these are in fact the most effective items to use in the investigation of equine personality.

A Tool for Every Job: Assessing the Need for a Universal Definition of Tool Use

Once considered only a human behavior, reports of tool use by a variety of animals have accumulated. Likewise, various definitions of tool use have also amassed. Although some researchers argue that understanding the evolutionary drivers of tool use is more important than identifying and describing these behaviors, the central issue of defining what constitutes tool use has not been fully addressed. Here we analyze prominent definitions of tool use and review the application of these definitions in scientific and educational literature. We demonstrate that many behaviors recently described as tool use do not meet criteria for prevalent definitions, while other neglected behaviors may constitute a form of tool use. These examples show how the use of inconsistent definitions of tool use in research can result in different conclusions from the same observations. Our aim is to demonstrate that a universally acceptable definition of tool use based on traditional, evolutionary, and operational understanding of behavior is needed. The rationale is that this review will stimulate the consistent and explicit use of specific terminology in tool use research. This would help define specific examples of each natural observation from a common measuring stick, allowing better comparative studies and classification of these unique behaviors.

Seasonal and Diurnal Variations in African Elephant ( Loxodonta africana ) and Black Rhinoceros ( Diceros bicornis ) Behavior in a Northern Climate Zoo

African elephants ( Loxodonta africana ) and black rhinoceroses ( Diceros bicornis ) are charismatic mammals that help draw visitors into zoological institutions. Because they evolved in the same habitat utilizing similar food resources, the two species have many physiological similarities yet behaviorally remain very different. Limitations of the zoo environment, such as constraints on exhibit size, social complexity, and behavior, may be associated with health and behavioral problems seen in both species and thought to be exacerbated in northern, temperate climates. The purpose of this study was to determine how the behavioral patterns of two large-bodied African ungulate species were affected by seasonal changes in a northern climate zoo. The behavior of three African elephants and three black rhinoceroses was observed for one year at Cleveland Metroparks Zoo. We found average resting levels of African elephants and black rhinos were similar to expected values based on data from wild and captive studies. Both species adapted their behavior to cope with high temperatures and increased sun exposure. Increased time spent inside during winter months was associated with decreased investigatory behaviors in elephants and decreased locomotion in rhinos. To increase species-typical behaviors, exhibits should include substrates for dusting, mud wallows, shade structures, and resting sites for all individuals. Time spent feeding may be increased through natural food items such as browse. Indoor exhibits should include environmental variation, enrichment, and adequate space so as to encourage these behaviors. Physiological and health measurements might be measured to determine sufficient levels of exercise for zoo-housed elephants and rhinos.

Food Preferences of the Brushtail Possum ( Trichosurus vulpecula )

The common brushtail possum ( Trichosurus vulpecula ) has been reported to eat vegetation, fruit, invertebrates, and occasionally fungi, eggs and meat. The relative preference between food types found in the wild, however, has not been investigated systematically in a controlled laboratory study. This research investigated captive possums’ food choice using two different methods of preference assessment. The first experiment involved a single stimulus assessment of possums’ (n = 20) consumption of individually presented food items. More than 75% of possums consumed berries, locusts and mushrooms but fewer than 50% of possums consumed fivefinger, raw chicken and eggs. The second experiment that used a paired stimulus assessment to establish relative preference for those foods revealed that no single food was preferred by all possums. Overall locusts were the most preferred food, followed in order of preference by berries, egg, mushrooms, chicken and foliage. The single stimulus preference assessment confirmed the palatability of foods. The paired stimulus assessment provided a rank order of food preferences.