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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 25, Issue 3, 2012

Research Paper

Ontogeny of Social Relations and Coalition Formation in Common Ravens (Corvus corax)

The social intelligence hypothesis, originally developed for primates to explain their high intelligenceand large relative brain size, assumes that challenges posed by social life in complex societies withmany group members lead to the evolution of advanced cognitive abilities. In birds, pair-bondedspecies have larger brains than non-pair bonded species, indicating that the quality of socialrelationships better predicts social complexity than group size. Ravens are a long-term monogamousand territorial species, renowned for their sophisticated socio-cognitive skills and complex socialrelationships. Notably, during their early years they live in fission-fusion-like non-breeder societies inwhich social relationships could be of particular importance. Here we observed the development ofdominance and affiliative relationships in 12 hand-raised captive ravens, examining the influence ofage, sex and kinship on social interactions. Furthermore, we investigated at which developmental stepa stable hierarchy emerged, whether third-party interventions played a role and how selectively birdsintervened in others’ conflicts. At 4-5 months post-fledging, we found an increase in socio-positivebehaviour and a decrease in aggression, along with the establishment of a linear dominance rankhierarchy. In line with kin selection theory, siblings exhibited a greater degree of tolerance andengaged in more socio-positive behaviour. In their first few months, ravens frequently intervened inothers’ conflicts but supported mainly the aggressor; later on, their support became more selectivetowards kin and close social partners. These findings indicate that ravens engage in sophisticatedsocial behaviours and form stable relationships already in their first year of life.

Preliminary Study of Object Labeling Using Sound Production in a Beluga

A beluga was tested to label objects using vocal symbols in order to form a bidirectional relationship between the visual symbols and sounds. In the Training session, the subject was first trained todistinguish four objects by four separate calls that he made. He learned to emit different calls corresponding to the sample stimuli. Next, these three recorded calls were played back to the subject,and he was required to select the objects (comparative stimuli) corresponding to the presented sound. He succeeded in correctly choosing the objects corresponding to the sounds played back. In the Test session, when a completely new recorded sound was presented to the subject, he could choose the correct object by matching the sample sound with the object. It is suggested that a beluga have realized bidirectional relationships or symmetrical relationship between visual symbols and sounds.This is a preliminary study that shows both production and comprehension of symbols in marine mammals.

The Role of Glucose on Executive Control Vigor: Evidence inSupport of Comparative Research

The central executive is theorized to be an overarching cognitive system responsible for coordinatingprocesses that enable self-control (i.e., inhibiting habitual responses), persistence at mental andphysical tasks, emotional regulation and working memory (Gailliot, 2008; Miller & Cohen, 2001).There is evidence that the executive system relies on glucose as its energy resource (Gailliot et al.,2007) and that when humans invoke the central executive they expend large quantities of glucose.When glucose levels are low, humans perform more poorly on other tasks that rely on the central executive (Gailliot et al., 2007). Similar results have been obtained with non-human animals. When dogs are required to exert self-control on an initial task they persist for a shorter duration at asubsequent unrewarding task and are more impulsive than if they were not required to exert selfcontrol(Miller, DeWall, Pattison, Molet, & Zentall, in press; Miller, Pattison, Rayburn-Reeves,DeWall, & Zentall, 2010). Given the similarities between human and non-human animals, further research on executive control processing and glucose depletion with non-human animals is encouraged. Such research may lead to interventions that sustain and replenish executive control.

How Selective is Social Learning in Dolphins?

Social learning is an important aspect of dolphin social life and dolphin behavioral development. Inaddition to vocal social learning, dolphins discover behaviors for foraging, play, and socialinteractions by observing other members of their social group. But dolphins neither indiscriminately observe nor mindlessly mimic other dolphins. To the contrary, dolphin calves are quite selective intheir choices of who to observe and/or imitate. Calves are most likely to learn foraging behaviorsfrom their mothers, but they are more likely to watch and reproduce the play behaviors of othercalves than the play behaviors of adult dolphins (including their mothers). But not all calves are equally likely to be good models. Instead, calves are more likely to observe and mimic the behaviorsof other calves that are producing either novel behaviors or more complex forms of behaviors that the observing calf already knows. As a result, there is a general tendency for calves to watch and learn from calves that are older than they are. But differences in age are only part of the story. In fact,dolphin personality may be more important than dolphin age in determining the efficacy of a model.

Using a Self-Organizing Map (SOM) and the Hyperspace Analog to Language (HAL) Model to Identify Patterns of Syntax and Structure in the Songs of Humpback Whales

Two different fully automated models were used to examine syntax and structure in humpback whalesong. Songs were initially classified via a Self-Organizing Map (SOM), and then examined, via the Hyperspace Analog to Language (HAL) model, for evidence of a type of higher level organization -global co-occurrence - found in human language. HAL was able to identify particular “classes” ofsong units which were used interchangeably to form patterns in the song, not unlike the use of  noun verb-direct object   in human language, where the noun, verb, or direct object can be any one of many possibilities from that particular class. Further, HAL identified specific patterns unique to the songsand their respective geographical areas. These patterns provide support for the idea that humpback whale songs are unique to specific region and may be transmitted culturally.