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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 3, 2013


Behavioral Development of Two Captive Mother-Calf Dyads of Bottlenose Dolphins (Tursiops truncatus) in the Calves’ First Year

This study investigated the development of suckling behavior, spatial relations, social behavior, and play behavior in 2 mother-calf dyads of bottlenose dolphins (Tursiops truncatus). Each dyad was observed 4 hours weekly throughout the calves’ 1st year. The dyads differed in calves’ sex and mothers’ parity. The dyad with the primiparous female needed more time to establish suckling and swimming routines. After the 3rd month, interactions with the mother (flipper-rub, rest together, social play, and calf watches mother) were significantly more frequent in the female calf, whereas interactions with the calves’ father (swim together, rest together, and social play) were significantly more frequent in the male calf. The calves showed high rates of object play and social play. They seemed to modify their type of play according to the opportunities they were offered. A mentally stimulating object was preferred to simpler toys. The knowledge of the details of mother-calf behavior helps to develop appropriate breeding conditions that are vital for the survival and well-being of captive dolphin calves.

Do Great Grey Owls Comprehend Means–end Relationships?

Cognitive abilities of the Great Grey Owl (Strix nebulosa) were tested with a means–end problem. Owls were presented the single baited string task and the string discrimination task. Our results suggest that owls failed to comprehend the physics underlying the object relationships involved in the tasks presented

Retention of a Brightness Discrimination Task in Paramecia, P. caudatum

Previous research into the possibility of learning in paramecia in this laboratory has shown that these organisms can learn to go to and remain in a specific location based on cathode shock reinforcement. The present experiment was designed to determine whether paramecia could retain (remember) the learned brightness discrimination task. The results indicate that the retention interval for this task in paramecia is shorter than 1 minute. It is possible that paramecia can remember this task for longer than a second but shorter than the 1-minute interval that was used during test. It is also possible that remembering for more than a few seconds requires a nervous system, which paramecia do not have.

A Zoo-housed Chimpanzee’s (Pan troglodytes) Responses to Potentially Arousing Stimuli

In Experiment 1, we wished to determine whether a singly-housed adult male captive chimpanzee could discriminate the behavioral categories of sex and aggression. He was reinforced for selecting sexual rather than aggressive images on a touch-screen computer in a two-choice discrimination paradigm. He showed no discrimination after 24 sessions with non-human photos, but immediately selected human sexual images at above-chance levels. To explore whether this differential discrimination was due to a preference for human sexual images, he was presented with images of humans versus non-humans under non-differential reinforcement in Experiment 2. He preferred human photos if the images depicted sex, but not if the images depicted aggression. To further explore these preferences in Experiment 3 the chimpanzee was presented with images of genitalia of non-humans versus humans, genitalia versus eyes, and finally female versus male genitalia of both non-humans and humans, using non-differential reinforcement. The chimpanzee preferred human to non-human genitalia, and eyes to genitalia, but did not prefer female to male genitalia. This chimpanzee’s unusual social environment may have interfered with species-typical social preferences.

Brief Report: Asian Elephants (Elephas maximus) may Demonstrate

Pioneering studies of animal personality appeared in the 1970s (e.g., Adamec, 1975; Buirski, Plutchik, & Kellerman, 1978; Stevenson-Hinde & Zunz, 1978). These studies proposed personality differences and examined behavioral tendencies that would be predicative of those personality traits. These studies began a surge of interest in consistent individual characteristics among individuals of various species, and during the past few years, research has begun to focus on animal personality more seriously. This line of research has resulted in a number of studies revealing individual differences in personality traits in such diverse species as primates, marine mammals, insects, fish, invertebrates, and birds (Gosling, 2001). Animal personality is defined as an individual animal’s unique and stable patterns of behavior (Gosling, 2001). Based on this definition, there are often two main goals of animal personality research: 1) determine if individuals within a species exhibit distinctive patterns of behavior and 2) determine if these patterns are consistent and stable over time and in a variety of contexts.