Journal of Comparative Psychology

A comparative study of caching and pilfering behavior in two sympatric species, least chipmunks (Tamias minimus) and eastern chipmunks (Tamias striatus).
We captured least chipmunks ( Tamias minimus ) and eastern chipmunks ( T. striatus ) from overlapping populations and assessed their comparative success at heterospecific pilfering in a naturalistic laboratory setting. The smaller species ( T. minimus ) found their competitors' caches more quickly and with less effort. We traced the success of least chipmunks to foraging behavior that targeted the vulnerabilities of eastern chipmunk caches, and a cache placement counterstrategy that protected their own food stores. The value of pilfered caches for least chipmunks was magnified by their smaller body size and the bigger cache size of their larger competitor. We suggest that heterospecific cache pilferage represents an especially lucrative foraging tactic for small foragers. (PsycINFO Database Record (c) 2011 APA, all rights reserved)
What makes an Australian sea lion (Neophoca cinerea) male's bark threatening?
In mammals, vocal signals are produced in many social contexts and convey diverse information about the emitter (social rank, individual identity, body size–condition). To understand their biological function, the authors find it is not only important to estimate the information about the signaler encoded in the signal but also to determine if and how this information is perceived by the receiver. In male pinnipeds (phocids, otariids, and odobenids) vocal signaling plays an important role in the breeding season during the defense of territories, females, or both. In this article, the authors investigated 2 key acoustic features that Australian sea lion ( Neophoca cinerea ) males most likely rely on to assess the threat level posed by potential rivals, by manipulating bark rhythmicity and spectral characteristics. Bark series that show accelerated rhythmicity and higher formants elicited stronger responses. (PsycINFO Database Record (c) 2011 APA, all rights reserved)
The use of the bared-teeth display during play fighting in Tonkean macaques (Macaca tonkeana): Sometimes it is all about oneself.
Play signals are viewed as important means by which animals inform each other that bites, strikes, and throws that occur during play fighting are indeed playful rather than serious. One such signal is the open mouth play face that is common in primates and many other mammals. Unfortunately, as most play fighting involves biting, it can be ambiguous as to whether any instance of opening the mouth is performed to communicate playful intent or is simply a preparation for biting. In this study, open mouths co-occurring with the bared-teeth display (teeth-baring) in Tonkean macaques were used to assess the context in which facial gestures only relevant for signaling (i.e., teeth-baring is not necessary for biting) are used during play. Two predictions arising from the hypothesis that play signals are used to facilitate playful contact were tested: that the open mouth with teeth-baring should (1) be most frequent preceding contact, and (2) that it should be performed most often when bites are directed at orientations that is visible to the recipient. The data only partially support these predictions. The open mouth with teeth-baring is also frequently used when a monkey withdraws from playful contact. Moreover, it is associated with bites to body targets, such as the rump, that offer little prospect for detection by the recipient; this supports the possibility that play signals may sometimes be emitted not to communicate with the partner but with the performer itself. Thus, play signals serve multiple functions during play fighting. (PsycINFO Database Record (c) 2011 APA, all rights reserved)
Turtles (Pseudemys nelsoni) learn about visual cues indicating food from experienced turtles.
We investigated whether turtles ( Pseudemys nelsoni ) could learn about a visual object cue to obtain food reinforcement by observing conspecifics that had learned the task. This study was designed with a three part task which, if completed by the observer turtles, would provide evidence of their abilities to learn from other turtles using stimulus enhancement, goal emulation, or copying. All four P. nelsoni turtles tested after observation of a trained demonstrator, whom they had direct access to during the demonstrator training trials, learned not only to follow another turtle to the stimulus indicating food, but also, in the absence of the demonstrator, to approach the correct stimulus regardless of spatial position. Therefore, all four P. nelsoni turtles tested showed evidence of stimulus enhancement learning. This is the first experimental study of social learning in any aquatic reptile demonstrating that they have the ability to learn from conspecifics. (PsycINFO Database Record (c) 2011 APA, all rights reserved)
Do bantams (Gallus gallus domesticus) amodally complete partly occluded lines? An analysis of line classification performance.
Humans perceive a line touching an edge of a large rectangle longer than the reality. Kanizsa (1979) has suggested that this illusion occurs because we perceive that the line is partly “hidden” behind the rectangle and automatically completes it. We tested whether bantams ( Gallus gallus domesticus ) would experience this perceptual phenomenon using a line classification task on the touch monitor, which was used in our previous study with rhesus monkeys and pigeons (Fujita, 2001). We trained three bantams to classify six lengths of black target lines into two categories, “short” or “long,” ignoring a gray rectangle (Experiment 1) or a gray area (i.e., a left or a right half of the monitor was filled with gray; Experiment 2) located at the same distance (8 pixels) from the target line. In the test, the gap between the line and the gray rectangle (or area) sometimes changed (0, 4, or 8 pixels; we labeled these stimuli as G0, G4, and G8 respectively). Both of the two successfully trained bantams showed an illusion for G0, but the direction of illusion was reversed; that is, they judged the line in G0 to be “shorter” than that in G4 and G8. Further analyses proved that neither the gaps between the target line and the gray rectangle nor the total widths of the stimuli could account for the bantams' responses. These results suggest that bantams do not complete the “occluded” portion even when identification of its shape is not required. (PsycINFO Database Record (c) 2011 APA, all rights reserved)
Acoustic and perceptual categories of vocal elements in the warble song of budgerigars (Melopsittacus undulatus).
The warble songs of budgerigars ( Melopsittacus undulatus ) are composed of a number of complex, variable acoustic elements that are sung by male birds in intimate courtship contexts for periods lasting up to several minutes. If these variable acoustic elements can be assigned to distinct acoustic-perceptual categories, it provides the opportunity to explore whether birds are perceptually sensitive to the proportion or sequential combination of warble elements belonging to different categories. By the inspection of spectrograms and by listening to recordings, humans assigned the acoustic elements in budgerigar warble from several birds to eight broad, overlapping categories. A neural-network program was developed and trained on these warble elements to simulate human categorization. The classification reliability between human raters and between human raters and the neural network classifier was better than 80% both within and across birds. Using operant conditioning and a psychophysical task, budgerigars were tested on large sets of these elements from different acoustic categories and different individuals. The birds consistently showed high discriminability for pairs of warble elements drawn from between acoustic categories and low discriminability for pairs drawn from within acoustic categories. With warble elements reliably assigned to different acoustic categories by humans and birds, it affords the opportunity to ask questions about the ordering of elements in natural warble streams and the perceptual significance of this ordering. (PsycINFO Database Record (c) 2011 APA, all rights reserved)
Flexible route selection by pigeons (Columba livia) on a computerized multi-goal navigation task with and without an “obstacle”.
The ability to select efficient routes while reaching several locations, in situations addressed as the “traveling salesperson problem (TSP)”, seems to play an important role in the lives of nonhuman species as well as humans. One of our previous studies with pigeons ( Columba livia ) used different variations of computerized navigation tasks to move a target to one or more goals, and showed that the birds consistently exhibited tendencies to visit the nearest goal first (Miyata & Fujita, 2010). Is this inflexible tendency consistent across all situations, or is it abandoned if it leads to a nonefficient strategy? The present study compared pigeons' route selection strategies in two-goal navigation tasks with and without having an L-shaped line as an obstacle barrier between the starting location of the target and the nearer goal. The pigeons frequently started by visiting the nearer goal in trials with no obstacles, whereas in trials having obstacles the birds often visited the farther goal first. For the detour trials with obstacles, the birds started from visiting the farther goal significantly more often than chance, even though disparity between the two traveling sequences was relatively small. The data demonstrated a case in which a tendency to visit the nearest goal was flexibly abandoned when the route required a detour behavior. Detailed analyses of the movement paths further suggest that the pigeons made decisions to choose a farther goal during the initial few steps, although a past history of reinforcement to avoid the barrier might have guided the birds' behavior. (PsycINFO Database Record (c) 2011 APA, all rights reserved)
The limits of endowment effects in great apes (Pan paniscus, Pan troglodytes, Gorilla gorilla, Pongo pygmaeus).
The endowment effect describes the bias that people often value things that they possess more than things they do not possess. Thus, they are often reluctant to trade items in their possession for items of equivalent value. Some nonhuman primates appear to share this bias with humans, but it remains an open question whether they show endowment effects to the same extent as humans do. We investigated endowment effects in all four great ape species ( Pan paniscus , Pan troglodytes , Gorilla gorilla , Pongo pygmaeus ) by varying whether apes were endowed with food items (Experiment 1, N = 22) or tools that were instrumental in retrieving food (Experiment 2, N = 23). We first assessed apes' preferences for items of a pair and their willingness to trade items in their possession. We then endowed apes with one item of a pair and offered them to trade for the other item. Apes showed endowment effects for food, but not for tools. In Experiment 3, we endowed bonobos (N = 4) and orangutans (N = 5) with either one or 12 food items. Endowment effects did not differ between species and were not influenced by the number of endowed food items. Our findings suggest that endowment effects in great apes are restricted to immediate food gratification and remain unaffected by the quantity of food rewards. However, endowment effects do not seem to extend to other, nonconsumable possessions even when they are instrumental in retrieving food. In general, apes do not show endowment effects across a range of different commodities as humans typically do. (PsycINFO Database Record (c) 2011 APA, all rights reserved)
Can captive orangutans (Pongo pygmaeus abelii) be coaxed into cumulative build-up of techniques?
While striking cultural variation in behavior from one site to another has been described in chimpanzees and orangutans, cumulative culture might be unique to humans. Captive chimpanzees were recently found to be rather conservative, sticking to the technique they had mastered, even after more effective alternatives were demonstrated. Behavioral flexibility in problem solving, in the sense of acquiring new solutions after having learned another one earlier, is a vital prerequisite for cumulative build-up of techniques. Here, we experimentally investigate whether captive orangutans show such flexibility, and if so, whether they show techniques that cumulatively build up (ratchet) on previous ones after conditions of the task are changed. We provided nine Sumatran orangutans ( Pongo pygmaeus abelii ) with two types of transparent tubes partly filled with syrup, along with potential tools such as sticks, twigs, wood wool and paper. In the first phase, the orangutans could reach inside the tubes with their hands (Regular Condition), but in the following phase, tubes had been made too narrow for their hands to fit in (Restricted Condition 1), or in addition the setup lacked their favorite materials (Restricted Condition 2). The orangutans showed high behavioral flexibility, applying nine different techniques under the regular condition in total. Individuals abandoned preferred techniques and switched to different techniques under restricted conditions when this was advantageous. We show for two of these techniques how they cumulatively built up on earlier ones. This suggests that the near-absence of cumulative culture in wild orangutans is not due to a lack of flexibility when existing solutions to tasks are made impossible. (PsycINFO Database Record (c) 2011 APA, all rights reserved)

Journal of Comparative Psychology - Vol 125, Iss 4