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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 36, 2023

Research Article

Pigeons (Columba livia) distinguish between absence of events and lack of evidence in contingency learning

When information about an event is perceptually occluded, individuals might recognize that the event might be present but that they cannot detect it because of the occluder. In such situations, an individual should continue to believe that the prevailing contingencies have not changed. This is in stark contrast to conditions where an expected event is explicitly absent, which should lead the individual to update their contingency knowledge. In an autoshaping procedure, we tested whether pigeons can discriminate conditions of perceptual ambiguity from perceptual certainty. Pigeons first learned to peck at two Pavlovian visual cues, followed by extinction of one of the cues. During extinction, the feeder was occluded by a metal shield for pigeons in Group Occluded, while the metal shield was placed next to but not covering the feeder for pigeons in Group Un-Occluded. On a final test with the metal shield removed, pigeons in Group Un-occluded pecked less at the extinguished cue than at the un-extinguished cue; while pigeons in Group Occluded pecked at an equally high rate to both cues. These results replicate in pigeons similar results reported in rats by Waldmann et al. (2012), and show that pigeons are able to discriminate conditions of certainty from conditions of ambiguity.

An Ecological Approach to the Effects of Water-Source Locations and Time-Based Schedules on Entropy and Spatio-Temporal Behavioral Features

In behavior analysis, the modulation of the effect of time-based schedules by the spatial characteristics of the environment has been scarcely studied. Furthermore, the spatial organization of behavior, despite its ubiquity and ecological relevance, has not been widely addressed. The purpose of the present work was to analyze the effect of water delivery location (peripheral vs. central) on the spatial organization of water-feeding behavior under time-based schedules. One group of rats was exposed to a Fixed Time 30 s-water-delivery schedule and a second group to a Variable Time 30 s schedule. For both groups, in the first phase, the water dispenser was located in the perimetral zone. In the second condition, the water dispenser was located in the central zone. Each location was presented for 20 sessions. Rat’s trajectories, distance to the dispenser, accumulated time in zones, and entropy measures were analyzed. A differential effect of the location of water delivery in interaction with the time-based schedule was observed on all the analyzed spatial qualities of behavior. The findings are discussed in relation to the ecological proposal of Timberlake's behavioral systems.


Hierarchical structure and feeding behaviours of free-range hens (Gallus gallus domesticus).

Chickens (Gallus gallus domesticus) are a social species and will form a hierarchy through agonistic dyadic encounters. This hierarchy will affect how different members of the flock access food, which may affect the specific feeding behaviours of the hens. The hierarchy of a 20-hen flock was determined by analysing videoed dyadic encounters between the hens and creating a dominance matrix. The feeding behaviours were assessed by simultaneously offering free food via a feeder and food distributed in the grass requiring foraging. Overall, all hens preferred to forage, however, significantly more dominant birds ate at the feeder than neutral or subordinate birds. Foraging is a natural behaviour that chickens will innately perform and is related to a positive welfare state. The methodology for determining the flock hierarchy and measuring feeding choices could be tested within the intensive farming environment to elucidate potential effects of dominance on feeding methods in commercial hens.

Training Honey Bees (Apis mellifera) to Push a Cap: Shaping, Observational Learning, and Memory

The cap pushing response (CPR) is a free flying technique where honey bees are trained to fly to a target where they push a cap to reveal a hidden food source. In this paper, we report the results of three studies. First, we provide information on three techniques used to shape the CPR. Second, we provide preliminary data suggesting that honey bees can learn the CPR through observing a previously shaped bee. Finally, we provide data on the ability of a honey bee to recall the CPR response. In addition to the three studies, we also continue to advocate for the use of Observation Orientated Modeling (OOM) for comparative investigations.

Use of water as a tool by a beluga (Delphinapterus leucas)

Captive belugas (Delphinapterus leucas) often spit water as object play. One female beluga spit water at a ball to obtain it for play. We examined whether or not this behavior could be considered a tool-use behavior. When the ball was placed 10 cm from the poolside, the beluga poked the ball with her rostrum, while she often spit water at the ball at 50cm. This water-spitting behavior became more predominantly when the ball was placed at 30 cm or farther, corresponding to the maximum distance she could reach, suggesting her understanding of the cause-effect relationship. Next, the two balls were placed at 30 cm and 60 cm, and one was placed inside the rings, so it would not be easy to move it out by water-spitting. When the closer ball was placed in the ring, she tried to spit water at the ball farther away but without the ring, suggesting an understanding of efficiency in tool use. Furthermore, during this study, the beluga showed the behavior of throwing the ball obtained by spitting water at another one with her mouth. This generalization may be based on the causal understanding established through water-spitting.

  • 1 supplemental ZIP
  • 5 supplemental files

Welfare Issues Associated to a Pack Size Change in Captive Iberian Wolves (Canis lupus signatus): A Case of Study

Maintaining biologically functional and compatible social groups is a primary welfare concern for captive animals. The aim of this study was to determine the effect of a pack size change -due to a new yearling- on the daily activity, use of space and inter-individual distance in a mated pair of Iberian wolves (Canis lupus signatus) housed at the Barcelona Zoo. Multifocal sampling methods were used for data collection, and instantaneous scans were made at 15-min intervals during 10-h sessions. 432 sampling points were balanced for the daily periods – morning, midday, and afternoon - for two different phases: dyad and triad phase. The subjects studied during the dyad phase - from April to May 1999 - were the mated pair. For the triad phase - from April to May 2000 – we studied the mated pair and the new yearling. When comparing these two study phases, there were statistically significant differences for the daily activity and the use of space. The mated pair used the space more homogenously during the triad phase. In the same phase, the inter-individual distance between the mated pair was statistically significantly closer in the morning and in the midday. The mated pair also showed individualized results for their daily activity, use of space and inter-individual proximity during the triad phase. Increasing understanding about the pack size enables the improvement of management to provide wolf packs with the most appropriate social environments.

Raptors’ Natural History Influences Their Response to the String-Pull Task

Largely due to the small number of individuals in captivity, birds of prey remain an understudied, but promising, group for animal cognition research. Variations on the classic string-pulling task have been applied across species to evaluate abilities such as associative learning, means-end understanding, and insight problem solving. Previous research has examined only a few species of raptor on the task such as the Harris’s hawk, great grey owl, and turkey vulture. Here, we explored how 1-3 individuals from each of seven raptor species (turkey vulture, Cathartes aura; barn owl, Tyto alba; western screech owl, Megascops kennicottii; eastern screech owl, Megascops asio; red-tailed hawk, Buteo jamaicensis; Swainson’s hawk, Buteo swainsoni; and Harris’s hawk, Parabuteo unicinctus) responded to a standardized vertical apparatus. Our goal was to replicate, diversify, and extend the literature by documenting how these different species approached the same problem. Two strings were tied around a perch, one of which was baited. Birds underwent multiple 60-min trials. At least one bird from four of the seven species retrieved the food reward. Three individuals retrieved the food consistently across trials, including the first recorded solving by a western screech owl. Birds displayed diverse apparatus-directed behaviors and solving methods which supported our predictions regarding sociality and predation method. We frame our findings as a roadmap for future researchers studying physical problem-solving by raptors.


  • 6 supplemental videos

I look at you to learn! Effects of the owner's sex on social learning in domestic dogs.

Dogs have been shown to be able to learn from a human demonstrator. However, to date, there have been no studies investigating the effect of the demonstrator’s sex on such learning. The aim of our study was to evaluate this effect by comparing an experimental condition in which dogs received a demonstration from their owner on how to manipulate one of two possible containers to obtain food and a control condition without any human demonstration. Each of these conditions was divided into two groups: male-owned and female-owned dogs. Overall, the dogs performed better in the experimental condition than the control condition. This was evidenced by a higher frequency of correct choices and opening the correct container, as well as a higher frequency of contact and gaze towards the demonstration. The female-owned group benefited from the demonstration by choosing the correct container more frequently in the experimental condition compared to the control. Conversely, male-owned dogs chose the correct container more often and looked more frequently at the demonstration than female-owned dogs, without differences between conditions. This could indicate a higher capacity for problem solving in this group of dogs beyond the human demonstration, and therefore wouldn't reflect a modulatory effect of the owner’s sex over social learning in particular. In conclusion, the sex of the demonstrator seems to have an effect on social learning in dogs when the demonstrator is a female owner. This might have an impact on several applied settings as well as sampling criteria in canine social cognition research.

Brief Report

An inexpensive low-cost video monitoring system for automated recording of behavior and ecological interactions

Active, real-time observation of behavior is a time-consuming task, which is heavily resource-limited. At the same time, simultaneous observation of several individuals is often paramount to increase statistical rigor and eliminate potential temporal or environmental bias, especially in natural settings. This paper describes a low-cost video recording system created by using “off-the-shelf” components. The system is easy to use and can automatically record a wide variety of behavior and related ecological interactions and evolutionary processes. The system is sensitive enough to record the behavior of a broad range of animals from planarians, and small insects to humans. It can also be used to measure the behavior of plants. The system will also work during daylight hours or at night and can run continuously and autonomously for 48 hours, or longer if the video capture is motion-triggered or if bigger capacity batteries and data storage facilities are used.