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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 34, 2021

Research Article

Decreased Key Pecking in Response to Reward Uncertainty Followed by Surprising Delay Extension in Pigeons

The Pavlovian autoshaping paradigm has often been used to assess the behavioral effects of reward omission on behavior. We trained pigeons to receive a food reward (unconditioned stimulus or UCS) following illumination of a response key (conditioned stimulus or CS). In Experiment 1, one group of pigeons was trained with two 100% predictive CS-UCS associations (reward certainty) and another group with two 25% predictive CS-UCS associations (reward uncertainty) for 12 sessions. In both groups, the two CS durations were 8 s. Then, in each group, the duration of one CS remained unchanged and that of the other CS was suddenly extended from 8 to 24 s for 6 sessions. In Experiment 2, some experienced individuals (from Experiment 1) and naïve individuals formed two groups trained with a 24-s CS throughout for 18 sessions. Our results show that pigeons (a) pecked less at the uncertain than the certain CS, (b) decreased and then increased CS-pecking after extending CS duration, especially in the certainty condition, (c) were unresponsive to the 24-s CS in the absence of previous experience, and (d) decreased their response rate close to the end of a trial irrespective of the reinforcement condition, CS duration, and amount of training. These results are discussed in relation to several theoretical frameworks.

Behavioural responses of Irrawaddy dolphins (Orcaella brevirostris) to a dead conspecific

Cetacean behaviour has long attracted scientific attention as humans endeavour to discover what makes these mammals so emotive and engaging. To date, much of this research has focussed on abundant and widely distributed cetacean species such as bottlenose dolphins ( Tursiops truncatus ) and humpback whales ( Megaptera novaeangliae ). As an endangered and often evasive species, research regarding Irrawaddy dolphin ( Orcaella brevirostris ) behaviour is limited. This study uses data collected by The Cambodian Marine Mammal Conservation Project, to investigate the behavioural responses of Irrawaddy dolphins towards a dead conspecific. During a routine boat survey of Cambodia’s Kep Archipelago, the carcass of an adult female Irrawaddy dolphin was recovered and attached to the stern of the research vessel and promptly towed to the research island for further examination. During this survey, there was a four-fold increase in the number of Irrawaddy dolphin groups observed compared to the seasonal average (post-monsoon), in addition to an atypically positive response towards the research vessel and an atypical increase in the number of behavioural events observed. These behavioural variations were believed to be in response to the towed dead conspecific. The authors propose future dedicated research to assess the complexity of wild Irrawaddy dolphin behaviour, cognition, and awareness, to robustly exemplify the species’ apparent sentience and intelligence.


Inducing Ethanol Tolerance in Free-Flying Honey Bees (Apis mellifera L.)

Ethanol dependency affects the health of more than 15 million adults in the United States of America. Honey bees have been used as a model for ethanol studies because of similarities in neural structure to vertebrates and their complex social behaviors. This study compares honey bee free-flight visitation to a food source after exposure to ethanol in aqueous sucrose.  Individual bees were followed making 6 attachment visits to a test-station containing 1M sucrose. After attachment, honey bees were randomly assigned to one of five groups: 0%, 2.5%, 5%, 10% EtOH, or a staged increase in ethanol concentrations (2.5%, 5%, 10%). The results indicate that honey bees tolerate up to 2.5% EtOH without avoidance or altered behavior, and up to 5% EtOH without avoidance but with slower trips. At 10% ethanol, attrition was 75% by the 18 th return trip.  In the staged increase in concentration, bees were more likely to return than bees that were offered 10% ethanol in sucrose solution after attachment. The results of this study imply that ethanol induced tolerance to the effects of ethanol can be achieved in honey bees through incremental increase in EtOH but only in terms of attrition.  Other measures of foraging efficiency did not show ethanol induced tolerance.   Understanding how ethanol tolerance develops in bees may provide insight into these processes in humans with minimized ethical considerations.

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Humans Discriminate Individual Large-Billed Crows and Individual Cats by Their Respective Vocalizations

Previous research has shown that human adults can easily discriminate two individual zebra finches (Taeniopygia guttata) by their signature songs, struggle to discriminate two individual rhesus monkeys (Macaca mulatta) by their calls, and are unable to discriminate two individual dogs (Canis familiaris) by their barks. The purpose of the present experiment was to examine whether acoustic discrimination of individual non-primate heterospecifics is limited to species producing stereotyped signature songs, or whether it is possible with the vocalizations of other species as well. This was tested here with the calls of individual large-billed crows (Corvus macrorhynchos) and the meows of individual domestic cats (Felis catus) using a forced-choice Same-Different Paradigm. Results show a high discrimination accuracy without prior training, although the scores obtained here for both species were lower than those in the zebra finch discrimination task. Discrimination accuracy of cat voices decreased when mean pitch was equalized between individuals, but was still possible without this cue. The removal of formant frequencies did not influence the discrimination, and there was no significant performance improvement across trials. These experiments suggest that individual acoustic discrimination is possible not only with species producing signature songs, but also with unlearned vocalizations of both birds and non-human mammals.

Deficient Play-Derived Experiences in Juvenile Long Evans Rats Reared with a Fischer 344 Partner: A Deficiency Shared by Both Sexes

Play fighting during the juvenile period has been shown to be an important experience for the development of sociocognitive skills and the underlying neural mechanisms that support them. Various paradigms have been used to deprive rats of play while still providing social contact. We used the paradigm of rearing a playful rat with a low-playing Fischer 344 (F344) partner to limit the play experienced by Long Evans (LE) rats during the juvenile period. This rearing paradigm has previously been shown to cause sociocognitive impairments in adulthood. In the present paper, we examined the play of same sex LE rats with LE or F344 partners at the peak juvenile period (around 35 days of age). F344 rats launched fewer playful attacks and when attacked, defended atypically compared to how LE do in LE-LE pairs. Playing with an F344 partner afforded LE rats fewer opportunities to engage in prolonged wrestling and fewer opportunities to ward off counterattacks (in which the defending rat becomes the attacker). In addition, there are fewer vocalizations emitted during the encounters in LE-F344 pairs and the types of calls most often emitted differed to those between LE-LE pairs. The altered play and communication experiences were equally present in male and female pairs. These findings are consistent with the hypothesis that, in such rearing paradigms, it is impoverished play experiences in the juvenile period that lead to impaired sociocognitive skills in adulthood.

Individual variability in visual recognition memory of black-handed spider monkeys (Ateles geoffroyi)

Recognition memory is an ability that allows animals to respond differentially to stimuli, individuals, or situations experienced in the past and plays an important role in foraging and social behavior. This ability has never been tested in black-handed spider monkeys (Ateles geoffroyi), but their social structure and diet force them to remember other individuals and food items. Therefore, they are a species in which to test whether their visual recognition memory depends on the retention interval (RI) and the list-length effect. Seven adult spider monkeys (Ateles geoffroyi) solved a delayed match-to-sample task where they had to touch a list of picture samples with different lengths (three, four, and five pictures). After that, they waited for different RIs (0, 15, and 30 s) to touch one of two pictures, signaling which was presented in the list. The group results indicate a high level of variability within individuals that overlap in each RI and position of the pictures for the three list-lengths. Individual plots and a nested ANOVA indicate effects of the RI, the list-length effect, and the position of the pictures on the list. The individual plots also show different strategies of the individuals to solve the task, such as only primacy, only recency, or both primacy and recency; but these strategies change as the RI increases. Based on these results, we recommend changes to the task and the statistical analysis for a better understanding of the underlying mechanism of recognition memory.

Comparison of exploratory behavior of two different animal species: woodlice (Armadillidium vulgare) and Rats (Rattus norvegicus)

Exploratory behavior is a commonly used instrument in the study of animal behavior in the laboratory, usually using rodents. The goal of the present study was to investigate the exploratory behavior of woodlice (Armadillidium vulgare) and compare to the behavior of rats (Rattus norvegicus). For this, we used two of two common rat laboratory tests: the square open-field and another inspired in the rat Light/Dark box. In a first test, rats were submitted to a square open-field; woodlice were also submitted to an open-field adapted to their size. In a second test, rats were submitted to a Light/Dark box and the woodlice were submitted to a Dry/Moist box designed to be equivalent to the rat apparatus but adapted to woodlice size. Results of the first test showed both rats and woodlice explored the square open-fields in similar ways, both in terms of frequencies of entries in the areas and also in terms of the time spent in them. Subjects of both species occupied the corners more than the areas close to the walls and these more than the central areas. Results of the second test showed a striking resemblance: Both species spent more time in the safe areas (dark or moist) and less time in the aversive areas (light or dry). Given this similarity, woodlice could be used as laboratory animals for behavioral studies with the advantages of occupying little room in animal places, are easy to catch in many places around university campuses and cost little to be fed.

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Brief Report

Understanding and assessing emotions in marine mammals under professional care

In the last 30 years, concerns about animal emotions have emerged from the general public but also from animal professionals and scientists. Animals are now considered as sentient beings, capable of experiencing emotions such as fear or pleasure. Understanding animals’ emotions is complex and important if we want to guarantee them the best care, management, and welfare. The main objectives of the paper are, first, to give a brief overview of various and contemporary assessments of emotions in animals, then to focus on particular zoo animals, that is, marine mammals, since they have drawn a lot of attention lately in regards of their life under professional care. We discuss here 1 approach to monitor their emotions by examining their laterality to finally conclude the importance of understanding animal emotion from a holistic welfare approach.


SI: ISCP bienniel meeting (2018)

Human and rat behavioral variability in the Dashiell maze: a comparative analysis

To assess their orientation in mazes, Dashiell (1930) developed a procedure allowing rats to reach the goal by utilizing paths of equal distance from the starting point. The main finding was the variety of new pathways the subjects took to reach the goal. Given the need for a task that might evaluate behavioral variability in humans, a simulation of the Dashiell procedure was developed: a virtual maze for human participants. With the goal of validating an animal model task for assessing human behavior variability, this study presents an experiment comparing rat and human performance when traversing a Dashiell maze. Results showed that rats in their maze and humans in the virtual version had similar path variability for reaching the goal; though humans showed higher dispersion from the mean. We conclude that the adaptive function of route variability in rats is similar to that in humans; thus the virtual Dashiell maze could become a reliable and straightforward task for assessing human behavior variability. Our study encourages the use of virtual mazes to compare behavioral variability between humans and other species.

Special Issue: Canine Research

Comparison of Paired- and Multiple-Stimulus Preference Assessments using a Runway Task by Dogs

Preference assessments identify foods that might be valued by an animal but do not capture differences in the magnitude of value. In combination with demand, the more effort required to acquire the commodity – the more valued and likely it is to function as an effective reinforcer for use in dog training. In the current experiment, two preference assessments' applicability was measured using a combination of choice assessment and effortful runway task. Eight dogs experienced a paired stimulus preference assessment and multiple stimulus without replacement preference assessments combined with a 3-m runway task. The preference assessments identified different most-preferred foods, but the same least-preferred foods. The reinforcer assessment results showed that the dogs moved faster to obtain their most preferred food as identified by the multiple stimulus without replacement assessment compared to the most preferred foods identified in the paired stimulus assessment. The paired- or multiple-stimulus-without-replacement preference assessments identified highly valued foods; however, the applicability of that commodity as a reinforcer was not independent of the assessment method. To ensure accurate reinforcer identification and consistency, a preference assessment should be conducted under similar conditions to that experienced when the reinforcer is used in training. Overall, the multiple stimulus without replacement preference assessment would be more useful to trainers, owners or scientists wanting to identify high-value foods for their animals to function as effective reinforcers for the elicitation of behaviors in a training context.