Abstract: This is the first study to investigate the short-term effects of high population density on captive chimpanzees (Pan troglodytes). Subjects of the study were 45 chimpanzees living in five different groups at the Yerkes Regional Primate Research Center. The groups were observed under two conditions: 1) when they had access to both the indoor and outdoor sections of their enclosures; 2) during cold days when they were locked into the indoor runs, which reduced the available space by more than half. Under the high-density condition, allogrooming and submissive greetings decreased, but juvenile play increased. Remarkably, the rate of various forms of agonistic behavior, such as aggression, bluff charge, bluff display, and hooting, occurred less frequently under the high-density condition. This general decrease in adult social activity, including agonistic behavior, can be interpreted as an inhibition strategy to reduce opportunities for conflict when interindividual distances are reduced. This strategy is probably effective only in the short run, however. Behavioral indicators of anxiety, such as rough scratching and yawning, showed elevated rates, suggesting increased social tension under the high-density condition.

Abstract: Variations in birth sex ratios and sex differences in juvenile mortality occur in a number of mammalian species, and in many cases have been linked to resource availability. Most of these biases in offspring sex ratios concern polygynous species with pronounced sexual dimorphism, and where females only are philopatric. Data on species with unusual life-history strategies, such as slight sexual dimorphism or dispersal by both sexes, are of particular interest. In this study of a natural herd of horses (Equus caballus) which experienced an eruptive cycle, and therefore a period of nutritional stress, male offspring had higher neonatal mortality rates in nutritionally poor years than in good ones, whereas “year quality” had no effect on the mortality of female offspring; year quality could therefore be used by mares as predictor of sex-specific offspring survival. We show that the environmental conditions that predicted lower survival of males were negatively related to their production: the birth sex ratio the following year was female-biased; and mares were less likely to produce a son when they had produced a son the preceding year. There was no significant effect of mother's parity, age or rank, or the timing of conception or birth on offspring sex ratios. The mechanism leading to biases in the birth sex ratio could have been the loss of male embryos by mares that did not foal. As there was no evidence for selective abortion of male foetuses in females that did foal the next year, it is not necessary to invoke maternal adjustment, though this remains a possibility. Finally, there was a suggestion that male offspring were more costly to raise than females, since mothers that reared a son in poor years tended to experience an increase in the interbirth interval between their two subsequent offspring.

Abstract: OBJECTIVE: To describe clinical findings, ultrasonographic features and outcome of injury to the branches of insertion of the superficial digital flexor (SDF) tendon in horses. DESIGN: Retrospective study of 14 cases. PROCEDURE: Fourteen Thoroughbred horses with tendonitis affecting the branches of insertion of the SDF tendon were examined for lameness, location and amount of swelling, and the presence of other musculoskeletal abnormalities. The flexor tendons were assessed by ultrasonographic examination, and recommendations were made for management of the cases. Outcome was assessed by re-examination of some horses, direct communication with the owner or trainer, and examination of race records. RESULTS: The lateral SDF branch was affected in 10 horses; the medial branch in three, and both branches in one horse. Two horses had concurrent injuries to the SDF tendon in the metacarpal region of the contralateral limb. Ultrasonographic findings included swelling of the affected SDF branch, peritendinous fluid accumulation, disruption of normal fibre alignment on sagittal scan, and variable loss of echogenicity. As healing occurred, there was return of normal echogenicity, but normal fibre alignment did not return completely and apparent adhesions formed between the affected SDF branch and adjacent structures. Seven of 10 horses which returned to their previous use were able to compete without further tendon injury. Recurrence of injury occurred in one case, and another two horses developed tendonitis in the metacarpal region. One horse was retired from racing but was able to compete at dressage without recurrence of injury. Two horses were retired for breeding without returning to training, and one horse was sold and lost to follow up but did not race. CONCLUSION: The prognosis is fair for return to previous use following injury to the branches of insertion of the SDF tendon in athletic horses.

Abstract: Individual behavioural reactions of adult horses in a variety of experimental tests were compared with ratings by riding teachers. The tests were made in a non working situation, with the animals being released in an arena, a box (arena test, new object test, learning tests) or handled (new object/handling situation). The traits rated by teachers were fearfulness, nervousness, gregariousness and learning abilities at work (ridden or handled). Despite a great homogeneity in the reactions exhibited by the horses in the different situations, large individual differences were present. Correlations appeared between the reactivity in the arena test and the score of gregariousness, between the reactivity in the novel object test and the rating of nervousness when ridden, between the results in the handling test and the rating of general fearfulness and between the ability to memorise an instrumental task and the score of general learning ability. Such results strengthen the idea that there are underlying behavioural dispositions that are stable across situations and that the experimental tests may be good predictors of the temperament in untrained animals.

Abstract: This series of studies investigated horses' ability to learn the concept of sameness under several different conditions. Before experimentation began, three horses were shaped to touch individually presented stimuli with their muzzles, and then to make two responses to two matching cards from an array of three. A modified version of the identity matching-to-sample (IMTS) procedure was used to present stimuli in a variety of configural arrangements on a barn wall (Experiment 1 and Experiment 2), and on a flat panel mounted to a barn door (Experiment 3). The task in each experiment was to select the two stimulus cards that were the same (either circles or Xs) and to avoid the nonmatching stimulus card (either a star or a square). In Experiment 1, the mean accuracy rate for selecting the matching alternatives was 74%. The horses' accuracy levels reached a mean level of 83% during Experiment 2, in which they received additional trials and an intermittent secondary reinforcement schedule. In Experiment 3, when the stimuli were moved further apart from each other within arrangements and were presented on a novel background, the mean accuracy rate was 73%. These data demonstrate that horses can learn complex discrimination problems involving the concept of sameness, and that they are able to generalize this learning to a novel stimulus presentation situation. These results also suggest that a relational discrimination test may be useful for assessing horses' learning ability and the level of training appropriate for individual horses.