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Thomsen, L. R., Campbell, R. D., & Rosell, F. (2007). Tool-use in a display behaviour by Eurasian beavers (Castor fiber). Anim. Cogn., .
Abstract: Tool use is rare amongst rodents and has never been recorded in connection with agonistic displays. We witnessed a behaviour, stick display (StD), involving tool use in free-living Eurasian beavers (Castor fiber) that we conclude is a display behaviour. Two beavers were the main performers of the signal that was observed in at least six beavers from three families. Beavers reacted to displays by increased evasive and agonistic behaviours compared with their usual behavioural patterns when at territory borders. The behaviour was almost exclusively seen between rivals at territory borders. We suggest that the display is used in agonistic encounters, mainly in a territorial context.
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Tibbetts, E. A., & Dale, J. (2007). Individual recognition: it is good to be different. Trends. Ecol. Evol, 22(10), 529–537.
Abstract: Individual recognition (IR) behavior has been widely studied, uncovering spectacular recognition abilities across a range of taxa and modalities. Most studies of IR focus on the recognizer (receiver). These studies typically explore whether a species is capable of IR, the cues that are used for recognition and the specializations that receivers use to facilitate recognition. However, relatively little research has explored the other half of the communication equation: the individual being recognized (signaler). Provided there is a benefit to being accurately identified, signalers are expected to actively broadcast their identity with distinctive cues. Considering the prevalence of IR, there are probably widespread benefits associated with distinctiveness. As a result, selection for traits that reveal individual identity might represent an important and underappreciated selective force contributing to the evolution and maintenance of genetic polymorphisms.
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Tomonaga, M. (2007). Relative numerosity discrimination by chimpanzees (Pan troglodytes): evidence for approximate numerical representations. Anim. Cogn., .
Abstract: Two adult chimpanzees were trained on a relative “numerosity” discrimination task. In each trial, two arrays containing different numbers of red dots were presented on a CRT monitor. The subjects were required to choose the array containing the larger number of dots. In Experiment 1, using numerosities between 1 and 8, 28 different pairs were presented repeatedly, and accuracy scores were analyzed to explore which cues the chimpanzee subjects utilized to perform the task. Multiple regression analyses revealed that the subjects' performance was (1) not simply controlled by the “numerical” difference between arrays, but that it was (2) best described by Fechner's Law-that is accuracy increased linearly with the logarithmic value of the numerical difference between arrays divided by the number in the larger of the two arrays. This relationship was maintained when using much larger numerosities (Experiment 3). In Experiment 2, the chimpanzees were tested on the effects of total area and density by manipulating dot size and presentation area. The results revealed that these factors clearly affected the subjects' performance but that they could not alone explain the results, suggesting that the chimpanzees did use relative numerosity difference as a discriminative cue.
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Valderrabano-Ibarra, C., Brumon, I., & Drummond, H. (2007). Development of a linear dominance hierarchy in nestling birds. Anim. Behav., 74(6), 1705–1714.
Abstract: Theoreticians propose that trained winning and losing are important processes in creating linear animal dominance hierarchies, and experiments have shown that both processes can occur in animals, but their actual roles in creating natural hierarchies are unknown. We described agonism in 18 broods of three blue-footed boobies, Sula nebouxii, a species for which trained winning and losing have been demonstrated, to infer how these processes generate and maintain a natural hierarchy. Ranks in the linear hierarchy that emerged in every brood were initially assigned by asymmetries in age, size and maturity, which led to differences between broodmates in levels of expressed and received aggression and, consequently, to differences in the training of their aggressiveness and submissiveness. Later, ranks appeared to be maintained by the chicks' acquired aggressive and submissive tendencies combined with ongoing effects of persisting differences in size and maturity. Our results suggest that trained winning and trained losing are important in the construction of booby hierarchies but that these two axes of learning are largely independent. Increase in submissiveness occurs over a period of about 10-20 days, and the level of submissiveness reached varies with the amount of aggression received. After training, submissiveness is apparently maintained by a lower level of aggression and increasing use of threats. Threats become increasingly effective as chicks age, but are never as effective as attacks.
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Valero, A., & Byrne, R. (2007). Spider monkey ranging patterns in Mexican subtropical forest: do travel routes reflect planning? Anim. Cogn., 10(3), 305–315.
Abstract: Although it is well known that frugivorous spider monkeys (Ateles geoffroyi yucatanensis) occupy large home ranges, travelling long distances to reach highly productive resources, little is known of how they move between feeding sites. A 11 month study of spider monkey ranging patterns was carried out at the Otochma’ax Yetel Kooh reserve, Yucatán, Mexico. We followed single individuals for as long as possible each day and recorded the routes travelled with the help of a GPS (Global Positioning System) device; the 11 independently moving individuals of a group were targeted as focal subjects. Travel paths were composed of highly linear segments, each typically ending at a place where some resource was exploited. Linearity of segments did not differ between individuals, and most of the highly linear paths that led to food resources were much longer than the estimate visibility in the woodland canopy. Monkeys do not generally continue in the same ranging direction after exploiting a resource: travel paths are likely to deviate at the site of resource exploitation rather than between such sites. However, during the harshest months of the year consecutive route segments were more likely to retain the same direction of overall movement. Together, these findings suggest that while moving between feeding sites, spider monkeys use spatial memory to guide travel, and even plan more than one resource site in advance.
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Versace, E., Morgante, M., Pulina, G., & Vallortigara, G. (2007). Behavioural lateralization in sheep (Ovis aries). Behav. Brain. Res., 184(1), 72–80.
Abstract: This study investigates behavioural lateralization in sheep and lambs of different ages. A flock was tested in a task in which the animals were facing an obstacle and should avoid it on either the right or left side to rejoin flock-mates (adult sheep) or their mothers (lambs). A bias for avoiding the obstacle on the right side was observed, with lambs apparently being more lateralized than sheep. This right bias was tentatively associated with the left-hemifield laterality in familiar faces recognition which has been documented in this species. Differences between adult sheep and lambs were likely to be due to differences in social reinstatement motivation elicited by different stimuli (flock-mates or mothers) at different ages. Preferential use of the forelegs to step on a wood-board and direction of jaw movement during rumination was also tested in adult animals. No population bias nor individual-level lateralization was observed for use of the forelegs. At the same time, however, there was a large number of animals showing individual-level lateralization for the direction of jaw movement during rumination even though there was no population bias. These findings highlight that within the same species individual- and population-level lateralization can be observed in different tasks. Moreover, the results fit the general hypothesis that population-level asymmetries are more likely to occur in tasks that require social coordination among behaviourally asymmetric individuals.
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Vervaecke, H., Stevens, J., Vandemoortele, H., Sigurjönsdöttir, H., & De Vries, H. (2007). Aggression and dominance in matched groups of subadult Icelandic horses (Equus caballus). J. Ethol., 25(3), 239–248.
Abstract: Abstract We studied sex differences in the nature of aggression and dominance behaviour in two newly formed groups of 1-year-old Icelandic horses. One herd contained nine geldings, the other nine mares. The groups were matched with regard to dominance-determining traits such as age, weaning age, composition of native herd, social experience, genetic origin, body condition and maternal dominance status. High-ranking individuals of both sexes were more aggressive, high-ranking males were older, and high-ranking females had a better body condition. Frequencies of aggressions were similar in both groups. The mares reacted significantly more by showing submission upon an aggression rather than by not responding or by escalating the aggression. For the geldings, this difference was not observed due to a lower tendency to submit. A linear dominance hierarchy was found in both groups. David`s scores provided additional information regarding cardinal rank distances and were used to calculate steepness of hierarchies. The female hierarchy was somewhat steeper compared to the male hierarchy, suggesting somewhat lower despotism among males. This was mainly a consequence of the lower unidirectionality in male submission. Male contests occurred predominantly between dyads at top and mid positions, suggesting a low degree of acceptance of the hierarchy.
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Voelkl, B., & Huber, L. (2007). Common marmosets (Callithrix jacchus) do not utilize social information in three simultaneous social foraging tasks. Anim. Cogn., 10(2), 149–158.
Abstract: Abstract Social foraging is suggested to increase foraging efficiency, as individuals might benefit from public information acquired by monitoring the foraging activities of other group members. We conducted a series experiments with captive common marmosets (Callithrix jacchus) to investigate to what extent marmosets utilize social information about food location when foraging simultaneously with conspecifics. Subjects were confronted with dominant and subordinate demonstrators in three experiments which differed in the amount of information about food location available to the demonstrators. In all three experiments, the focal subjects` performance in the social condition was not enhanced in comparison to a non-social control condition. Because we could rule out kleptoparasitism and aggressive displacements as explanations, we argue that the subjects tendency for scramble competition by avoiding others and dispersing over the foraging area seems to inhibit or mask the acquisition of social information about the location of rewarded patches.
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Ward, C., & Smuts, B. B. (2007). Quantity-based judgments in the domestic dog (Canis lupus familiaris). Anim. Cogn., 10(1), 71–80.
Abstract: We examined the ability of domestic dogs to choose the larger versus smaller quantity of food in two experiments. In experiment 1, we investigated the ability of 29 dogs (results from 18 dogs were used in the data analysis) to discriminate between two quantities of food presented in eight different combinations. Choices were simultaneously presented and visually available at the time of choice. Overall, subjects chose the larger quantity more often than the smaller quantity, but they found numerically close comparisons more difficult. In experiment 2, we tested two dogs from experiment 1 under three conditions. In condition 1, we used similar methods from experiment 1 and tested the dogs multiple times on the eight combinations from experiment 1 plus one additional combination. In conditions 2 and 3, the food was visually unavailable to the subjects at the time of choice, but in condition 2, food choices were viewed simultaneously before being made visually unavailable, and in condition 3, they were viewed successively. In these last two conditions, and especially in condition 3, the dogs had to keep track of quantities mentally in order to choose optimally. Subjects still chose the larger quantity more often than the smaller quantity when the food was not simultaneously visible at the time of choice. Olfactory cues and inadvertent cuing by the experimenter were excluded as mechanisms for choosing larger quantities. The results suggest that, like apes tested on similar tasks, some dogs can form internal representations and make mental comparisons of quantity.
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Warneken, F., Hare, B., Melis, A. P., Hanus, D., & Tomasello, M. (2007). Spontaneous Altruism by Chimpanzees and Young Children. PLoS Biol, 5(7), e184 EP -.
Abstract: <p>Experimental evidence reveals that chimpanzees will help other unrelated humans and conspecifics without a reward, showing that they share crucial aspects of altruism with humans.</p>
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