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.

Abstract: Processed feed for stabled horses is usually presented in buckets or mangers, and is easily and rapidly consumed. Foraging devices based on the Edinburgh foodball can be used to provide part of the ration. Current designs are all placed on the floor, raising concerns regarding ingestion of foreign materials along with the dispensed food. Alternative devices were evaluated, when presented within suitable, clean containers to prolong food-handling times but avoid such issues. In four Latin square designed replicated trials we investigated behaviour of 12 stabled horses with three foraging devices. These were separately presented for 5 min, varied in sensory complexity (round, square, polyhedral) and contained 500 g high fibre pellets. In Trials 1 and 2 six geldings were presented with devices in buckets then mangers. All individuals foraged successfully from at least one device and behaviour was compared. However, all individuals exhibited some frustration while using the devices (either pawing or biting them). Horses frequently removed the devices from the buckets in Trial 1 terminating these sessions. In Trial 2 mean device foraging duration was ranked polyhedral > round > square. Mean pawing rate in Trial 2 was calculated for horses (frequency of pawing per individual/summed duration manipulation and foraging) and was highest with square (0.11, npawers = 6). In Trial 3 six stabled mares were presented with the same foraging devices in mangers. Mean foraging duration with devices again ranked polyhedral > round > square. Mean pawing rate was highest with round device (0.08, npawers = 4). Trial 4 investigated behaviour of six horses when devices initially containing five high fibre pellets became empty. Mean foraging duration with devices ranked round > polyhedral > square. Mean pawing rate was highest with square device (0.11, npawers = 4). All horses foraged successfully from at least one foraging device in buckets and mangers. Devices met initial objectives but the unpredictability of reward suggests a source of frustration and warrants further investigation.

Abstract: Chimpanzees (Pan troglodytes) know what others can and cannot see in a competitive situation. Does this reflect a general understanding the perceptions of others` In a study by Hare et al. (2000) pairs of chimpanzees competed over two pieces of food. Subordinate individuals preferred to approach food that was behind a barrier that the dominant could not see, suggesting that chimpanzees can take the visual perspective of others. We extended this paradigm to the auditory modality to investigate whether chimpanzees are sensitive to whether a competitor can hear food rewards being hidden. Results suggested that the chimpanzees did not take what the competitor had heard into account, despite being able to locate the hiding place themselves by the noise.

Abstract: Abstract  The issue whether non-human primates have other-regarding preference and/or inequity aversion has been under debate. We investigated whether tufted capuchin monkeys are sensitive to others’ reward in various experimental food sharing settings. Two monkeys faced each other. The operator monkey chose one of two food containers placed between the participants, each containing a food item for him/herself and another for the recipient. The recipient passively received either high- or low-value food depending on the operator’s choice, whereas the operator obtained the same food regardless of his/her choice. The recipients were either the highest- or lowest-ranking member of the group, and the operators were middle-ranking. In Experiment 1, the operators chose the high-value food for the subordinate recipient more frequently than when there was no recipient, whereas they were indifferent in their choice for the dominant. This differentiated behavior could have been because the dominant recipient frequently ate the low-value food. In Experiment 2, we increased the difference in the value of the two food items so that both recipients would reject the low-value food. The results were the same as in Experiment 1. In Experiment 3, we placed an opaque screen in front of the recipient to examine effects of visual contact between the participants. The operators’ food choice generally shifted toward providing the low-value food for the recipient. These results suggest that capuchins are clearly sensitive to others’ reward and that they show other-regarding preference or a form of inequity aversion depending upon the recipients and the presence of visual contact.

Abstract: Herbivores challenged by diets with high concentrations of tannins learn by individual experience to self-select medicinal compounds such as polyethylene glycol (PEG), which neutralizes the negative postingestive effects of tannins. We investigated the transmission of this acquired self-medicative behaviour from mother to offspring. One group of ewes (experienced, N = 8) was conditioned to associate the beneficial effects of PEG after consuming a tannin-rich diet. Ewes ingested a meal of high-tannin food and were then offered PEG. Subsequently, ewes ingested the same tannin-rich meal and were then offered a food (grape pomace; control) that did not have the medicinal effects of PEG. After conditioning, the experienced group and a naïve group of ewes (N = 8) were given a choice between the high-tannin food, PEG and grape pomace. Experienced ewes showed higher intake and preference for PEG than did naïve ewes (P < 0.05). Subsequently, experienced and naïve ewes with their naïve lambs, as well as a group of naïve lambs without their mothers (N = 8), were exposed to the tannin-rich diet, PEG and grape pomace. Lambs were then tested for their ability to self-medicate with PEG by offering them a choice between the tannin-rich diet, PEG and grape pomace. Lambs from experienced and naïve mothers showed a higher preference for PEG than did lambs exposed without their mothers (P = 0.05). Thus, the presence of the mother (experienced or naïve) was important for naïve lambs to learn about the medicinal benefits of PEG. We conclude that the mother's presence per se may increase the efficiency of creating new knowledge, such as preference for a medicine, within a group, beyond transmitting and maintaining this knowledge across generations.