![]() In those cases, a fast discounting of food value over time, i.e., a preference for immediacy, may be the most adaptive strategy ( Kagel et al., 1986 Stephens, 2008) and choices in several species have been described not to be consistent with rate maximization ( Stevens and Mühlhoff, 2012). However, several authors suggest that in some contexts, delaying food intakes might add additional risk to survival. From an evolutionary perspective, choices optimizing long-term gain over immediate benefits in foraging ( Stephens and Krebs, 1986 Kacelnik, 2003) or mating situations ( Stephens and Krebs, 1986 Stevens, 2010) should be selected for and, thus, found in a variety of species. The difficulties of non-human animals in controlling impulses seem to reflect primarily a cognitive problem. ![]() This is particularly true for several bird species, which hardly control an impulsive choice for longer than a few seconds in experimental situations (pigeons, Columba livia: Ainslie, 1974 Mazur, 1987 Logue et al., 1988 Green et al., 2004 African gray parrots, Psittacus erithacus: Vick et al., 2010 domestic fowl, Gallus gallus: Abeyesinghe et al., 2005). Impulse control develops slowly in children ( Mischel et al., 1989) and often represents serious difficulties to non-human animals ( Stephens and Anderson, 2001 Stevens et al., 2005 Evans and Beran, 2007a Anderson et al., 2010). The ability to overcome an impulsive choice-defined as the choice of the less desirable, immediate option, over a more desirable though delayed one ( Rachlin, 1974), has long been thought to be a uniquely human feature ( Burns and Powers, 1975 Logue, 1988 Rachlin, 2000). Taken together, these results suggest that, although crows may possess the cognitive abilities to judge quantities and to overcome an impulsive choice, they do so only in order to optimize the qualitative but not quantitative output in the exchange paradigm. All birds chose the higher quantities significantly more often, indicating that they can discriminate between quantities and that higher quantities are more desirable. We performed a preference test between one or more pieces of cheese in order to address whether crow poor performance could be due to an inability to discriminate between different quantities or not attributing a higher value to the higher quantities. We tested six captive crows – three individuals never exchanged the initial reward for a higher quantity the other three birds did exchange though at very low rates. After a short delay, individuals were asked to give back an initial reward (cheese) to the human experimenter in order to receive a higher amount of the same reward (two, four, or eight pieces). In the present study, we specifically investigated the ability of carrion crows to overcome an impulsive choice in a quantitative exchange task. Recently two corvid species, common raven ( Corvus corax) and carrion crow ( Corvus corone corone), exchanged food for a higher quality reward though seemed less capable of enduring delays when exchanging for the same food type in a higher quantity. However, studies on non-human primates revealed that some species are capable of enduring delays in order to get food of higher quality or quantity. The ability to control an immediate impulse in return for a more desirable – though delayed – outcome has long been thought to be a uniquely human feature. 4 Centre National de la Recherche Scientifique, UMR7178, Strasbourg, France.3 Institut Pluridisciplinaire Hubert CURIEN Strasbourg, Université de Strasbourg, Strasbourg, France.2 Department of Cognitive Biology, University of Vienna, Vienna, Austria.1 Konrad Lorenz Forschungsstelle, University of Vienna, Vienna, Austria.Wascher 1,2,3,4*, Valerie Dufour 3,4 and Thomas Bugnyar 1,2
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