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Schloegl, C., Kotrschal, K., & Bugnyar, T. (2008). Modifying the object-choice task: Is the way you look important for ravens? Behav. Process., 77(1), 61–65.
Abstract: Most animals seem to have difficulties in using gaze cues to find hidden food in object-choice tasks. For instance, chimpanzees usually fail in these tests, even though they are capable of following other's gaze geometrically behind barriers. Similar to chimpanzees, common ravens are skilled in tracking other's gaze but fail in object-choice tasks. We here explored whether procedural modifications, which had been used successfully in chimpanzees, would also yield positive results in ravens. In our modifications (a) the experimenter approached the cup while gazing at it, (b) the gaze cue was accompanied by a sound and (c) the experimenter could actually see the food while giving the gaze cue. Two out of seven birds performed above chance level in some of these conditions. However, we ascribe this improvement to the individuals' learning ability rather than to an understanding of the communicative nature of the task. This interpretation is further supported by results of a follow-up experiment suggesting that ravens may not rely on conspecifics' gaze cues for finding food caches in a natural foraging context. In sum, our results suggest that ravens may not transfer their gaze follow abilities to foraging situations involving hidden food.
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Schwab, C., Bugnyar, T., Schloegl, C., & Kotrschal, K. (2008). Enhanced social learning between siblings in common ravens, Corvus corax. Anim. Behav., 75(2), 501–508.
Abstract: It has been suggested that social dynamics affect social learning but empirical support for this idea is scarce. Here we show that affiliate relationships among kin indeed enhance the performance of common ravens, Corvus corax, in a social learning task. Via daily behavioural protocols we first monitored social dynamics in our group of captive young ravens. Siblings spent significantly more time in close proximity to each other than did nonsiblings. We subsequently tested birds on a stimulus enhancement task in model-observer dyads composed of both siblings and nonsiblings. During demonstration the observer could watch the model manipulating one particular object (target object) in an adjacent room. After removing the model, the observer was confronted with five different objects including the former target object. Observers from sibling dyads handled the target object for significantly longer periods of time as compared with the other four available objects, whereas observers from nonsibling dyads did not show a preference for the target object. Also, siblings matched the model's decision to cache or not to cache objects significantly more often than did nonsiblings. Hence, siblings were likely to attend to both, the behaviour of the model (caching or noncaching) and object-specific details. Our results support the hypothesis that affiliate relations between individuals affect the transmission of information and may lead to directed social learning even when spatial proximity has been experimentally controlled for.
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Selva, N., Cortés-Avizanda, A., Lemus, J. A., Blanco, G., Mueller, T., Heinrich, B., et al. Stress associated with group living in a long-lived bird. Biol Lett, .
Abstract: Many long-lived avian species adopt life strategies that involve a gregarious way of life at juvenile and sub-adult stages and territoriality during adulthood. However, the potential associated costs of these life styles, such as stress, are poorly understood. We examined the effects of group living, sex and parasite load on the baseline concentration of faecal stress hormone (corticosterone) metabolites in a wild population of common ravens (Corvus corax). Corticosterone concentrations were significantly higher in non-breeding gregarious ravens than in territorial adults. Among territorial birds, males showed higher stress levels than their mates. Parasite burdens did not affect hormone levels. Our results suggest a key role of the social context in the stress profiles of the two population fractions, and that group living may be more energetically demanding than maintaining a territory. These findings have implications for understanding hormonal mechanisms under different life styles and may inspire further research on the link between hormone levels and selective pressures modulating gregarious and territorial strategies in long-lived birds.
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Trim, C. M., Moore, J. N., & Clark, E. S. (1989). Renal effects of dopamine infusion in conscious horses. Equine Vet J Suppl, (7), 124–128.
Abstract: An ultrasonic flow probe was implanted around a branch of the left renal artery in five horses. The effects of dopamine were studied in the unsedated horses 10 days after surgery. Three experiments, separated by at least two days, were performed in random order on each horse. In two experiments, dopamine was infused intravenously for 60 mins at either 2.5 and 5.0 micrograms/kg bodyweight (bwt)/min. Saline was infused for 60 mins before and after each infusion, and for 180 mins in the third experiment as a control. Renal blood flow increased during administration of dopamine at both dose rates (P = 0.0001). Urine volume increased (P = 0.055), and osmolality decreased (P < 0.05), with infusion of dopamine at 5.0 micrograms/kg bwt/min. Arterial blood pressure and heart rate were not significantly affected. Fractional excretions of sodium and potassium were not significantly changed with dopamine infusion. The higher dopamine dose rate was accompanied by dysrhythmias in some horses.
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