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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 3, 2011

Research Paper

In-Air Auditory Psychophysics and the Management of a Threatened Carnivore, the Polar Bear (Ursus maritimus)

Management criteria for preventing biologically-significant noise disturbance in large terrestrial mammals have not been developed based on a sound, empirical understanding of their sensory ecology. Polar bear (Ursus maritimus) maternal denning areas on the coastal plain of Alaska’s North Slope hold large petroleum reserves and will be subject to increased development in the future. Anthropogenic noise could adversely affect polar bears by disrupting intra-specific communication, altering habitat use, or causing behavioral and physiological stress. However, little is known about the hearing of any large, carnivorous mammal, including bears; so, management criteria currently in use to protect denning female polar bears may or may not be proportionate and effective. As part of a comprehensive effort to develop efficient, defensible criteria we used behavioral psycho acousticmethods to test in-air hearing sensitivity of five polar bears at frequencies between 125 Hz and 31.5kHz. Results showed best sensitivity between 8 and 14 kHz. Sensitivity declined sharply between 14and 25 kHz, suggesting an upper limit of hearing 10-20 kHz below that of small carnivores. Low frequency sensitivity was comparable to that of the domestic dog, and a decline in functional hearingwas observed at 125 Hz. Thresholds will be used to develop efficient exposure metrics, which will be needed increasingly as the Arctic is developed and effects of disturbance are intensified by anticipated declines in polar bear health and reproduction associated with climate change driven sea ice losses.

Head and Foot Coordination in Head Scratching and Food Manipulation by Purple Swamp Hens ( Porphyrio porphyrio): Rules for Minimizing the Computational Costs of Combining Movements from Multiple Parts of the Body

Complex movements, such as placing food into the mouth, involve coordinating multiple limb segments. Given the degrees of freedom for one limb segment, the computational costs of such complex movements can be high. One way to reduce such costs is to limit the adjusting movements needed to achieve coordination of distal body parts to only one part of the body. For example, for scratching the head, the hand or foot needs to make contact with the head and this involves movements of the head, neck and torso, as well as those of the foot and leg, or hand and arm. In this situation, the foot or hand is raised to a specific location in space and then makes oscillatory movements, but it is movements by the head and neck that ensure appropriate contact is made with the head (Pellis, 2010). In this paper, whether such cost-saving rules apply across functional contexts is tested in the purple swamp hen by comparing head and foot coordination during head scratching and during food reaching and handling. This species uses its foot to grasp and hold a wide range of food items that are picked up in its bill. Comparison of hundreds of videotaped sequences revealed that, in both cases, the bird uses the same rule: that of making the accommodating movements with only one of those body parts, even when coordination requires movements of disparate parts of the body. These data show that there are likely common computational cost-saving rules that widely apply to movements occurring in many different functional contexts.

Are Monkeys Sensitive to the Regularity of Pay-off?

Animals commonly face fluctuations in their environment and resources. To maximize their benefits,they need to integrate the risks attached to potential pay-offs. We do not know, however, to what extent individuals account for irregularity in the latter. We tested the sensitivity of monkeys (Cebusapella, Macaca tonkeana, M. fascicularis) to the irregularity of pay-offs in two different tasks. In a first experiment, the subjects were given an exchange task where the reward probability varied between different conditions, but yielded the same average pay-off. There was no evidence of subjects favoring either condition, meaning that they behaved in accordance with the predictions ofthe classical decision theory (Expected Utility Theory). In a second experiment, we offered to subjects a choice between two options involving different pay-off regularity. In this case, a wide range of inter-individual variation was found in the choices of individuals. Whereas monkeys accepted irregular pay-off in a rational way, there were individual biases in their preferences. These results indicate that the preferences of animals in a risky situation were not unequivocally shaped by the environment in which species have evolved.

Encoding the Object Position for Assessment of Short Term Spatial Memory in Horses (Equus caballus)

In this study, the detour problem was combined with the classic delayed-response task to investigate equine short-term spatial memory. Test subjects were eight female horses, divided into two groups (A and B) of four subjects each. The motivating object was made to move and disappear behind one oftwo identical obstacles in a two-point-choice apparatus. After a 10 s (Group A) or 30 s (Group B) delay the animal was released to seek the object. Both groups made more correct (14.8 ± 1.3 forGroup A and 13.5 ± 3.1 for Group B, mean ± SD) than incorrect choices (5.3 ± 1.3 for Group A and6.5 ± 3.1 for Group B, mean ± SD) and the performance of each group was significantly above chance level (z = 4.14,  p = 0.000, for Group A and z = 3.02, p = 0.002, for Group B). Therefore, tested animals were able to recover the object by approaching the correct obstacle after 10 s or 30 s delays, showing that they had encoded and recovered from memory the existence of the target object and its location.

Comparing Object Play in Captive and Wild Dolphins

Examining the role of play as related to individual and group social development is important to understanding a species. The purpose of our study was to examine whether there is a difference in the frequency of object play exhibited by dolphins from two groups – one captive and one wild. Data were collected with underwater video, with resulting videos event sampled for bouts of play involving various objects used by dolphins. From 159 hr of video data, roughly 102 min featured object play: 75 min of dolphins from RIMS and 26 min for dolphins near Bimini. A total of 304 bouts of object play were documented from or between dolphins at RIMS, while 73 bouts were observed byor between dolphins around Bimini. Juvenile dolphins engaged in solo and mutual play more thantwice that of other aged dolphins from both study groups, although this result was not statistically significant. Similarly, male dolphins at RIMS exhibited object play slightly more than females, though this difference was not significant: at Bimini, male dolphins were not observed to play with objects during interactions with conspecfics (mutual) and engaged in object play about half as oftenas female spotted dolphins. Combining both study groups, dolphins played with about 23 different objects that were grouped into six categories: biological debris, human made objects, inanimate objects, other (e.g., wood, etc), people, and trash. The RIMS dolphins played most with all objects except people while Bimini dolphins interacted with sand more than any other object. Dolphins have been shown to exhibit higher cognitive functions, of which complex play is one example. The role of play in animals is considered important to development and maintenance of social relationships and to learning skills required ultimately for survival.