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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 24, Issue 2, 2011

Research Paper

Reward Probability and the Variability of Foraging Behavior in Rats

The connection between reduced reinforcement probability and increased behavioral variability hasbeen well established in recent years (Gharib, Gade, & Roberts, 2004; Stahlman, Roberts, & Blaisdell, 2010). Researchers have hypothesized that this relationship is an adaptive one - it is beneficial for animals to increase behavioral variability in response to low likelihood of success,because this increase in variability potentially allows them to discover new behavioral options that are more highly rewarded. We conducted a study to investigate the relationship between behavioral variability and reward probability in an ecologically valid experimental task. We trained rats tosearch for hidden food in the presence of either of two landmarks, each that signaled a different likelihood of reward (i.e., HI and LO). Variation in locations searched was higher in the presence ofthe LO probability landmark. These results build on prior findings that reward expectation drives behavioral variability.

Timing of Turn Initiations in Signed Conversations with Cross-Fostered Chimpanzees ( Pan troglodytes)

This study examined turn taking by adult and infant cross-fostered chimpanzees in one-on-one signed conversations with a human. The study identified turns as alternating, overlapping, or simultaneousand explored the timing of overlapping turn initiations in detail for both age groups. Adult chimpanzee turn taking was furthermore examined in two conditions; in the first condition the human responded to the chimpanzees with scripted probes and in the second condition the human signed freely. Results showed that the adult chimpanzees engaged in more alternating turns in the scripted condition and more overlapping turns in unscripted condition. In the interactions of the unscripted condition, the adult chimpanzees and the human partner initiated overlapping turns with nearly equal frequency, and the chimpanzees were likely to initiate overlap as the partner completed a turn. In comparable unscripted interactions, the infant chimpanzees initiated significantly more overlap thantheir partners and initiated overlap randomly throughout the partner’s sign. Results suggest that turntaking in the chimpanzees developed with experience.

Development and Validation of a Psychometric Tool forAssessing Impulsivity in the Domestic Dog ( Canis familiaris)

Impulsivity is a trait that has received much attention in humans, but in dogs impulsivity is illdefined, and previous studies have tended to focus on aggression, rather than its more pervasive effect on behavior. The objective of this study was to develop a valid psychometric assessment tool of impulsivity in dogs. An owner report questionnaire was constructed using items generated by a survey of experts. Five hundred and seventy one dog owners returned the questionnaire and data were subjected to principal components analysis, revealing a three-factor structure: Factor 1: Behavioral Regulation, Factor 2: Aggression & Response to Novelty, and Factor 3: Responsiveness. The resulting Dog Impulsivity Assessment Scale comprised of 18 items demonstrated evidence of reliability and validity.

Observational Learning in a Glaucous-winged Gull Natural Colony

The ability of the Glaucous-winged Gull (Larus glaucescens) to observationally learn has been investigated in their natural habitat, in a gull’s colony located on Toporkov Island (Comandorsky State Nature Reserve, Far East, Russia). The experiment was carried out in the gull’s breeding period, when each bird’s pair in the colony occupies and protects vigilantly their small nesting sites surrounded by those of neighboring pairs. The gulls chosen to be demonstrators were trained to solve two different tasks both of which were not part of the species’ behavioral repertoire. The first task was obtaining a bait placed by an experimenter into an opaque box within the bird's visual field ; the second one was choosing a red box from a set of four identically-looking boxes differing only incolor. In contrast to the demonstrator gulls, which needed considerably training, most observers (the gulls nesting side-by-side with the demonstrators) performed the same tasks correctly in the first trial.Thus, gulls have proven to be capable of successful learning to solve simple choice tasks by observing what their conspecifics are doing. Observational learning can be a way to distribute individual experience among the gulls in a colony. The ability to observationally learn quickly maybe one of the factors underlying a higher adaptive potential of these birds.

Beluga ( Delphinapterus leucas) Bubble Bursts: Surprise, Protection, or Play?

Cetaceans produce a variety of bubble displays, ranging from bubble streams to very large bursts of air. Previous research has indicated that different types of bubbles serve different functions. Using archival video data, we investigated the frequency and function of bubble behavior for four beluga mother-calf pairs housed at Sea World San Antonio (SWSA, 2007-2010). Bubble bursts, large,forceful bursts of air released underwater, were the most frequent form of bubbles produced. The mothers primarily produced bubble bursts while swimming with their calves whereas the calves produced the majority of their bubble bursts during solitary activities. These results suggest that mothers may use their bubble bursts as a protective behavior or warning to threatening stimuli (e.g., other belugas) whereas when threatening stimuli are not present calves may produce bubble bursts as a form of play. Additional research is necessary to better understand if these bubble displays areunder the intentional control of the animals producing them.