Abstract: Horses are likely to exhibit aggression when meeting for the first time. Therefore, this study compared 3 methods for mixing horses to evaluate their effectiveness in reducing aggressive interactions: (1) mixing pairs of horses in a paddock (P, 10 minutes, 15 tests), (2) introducing 1 unfamiliar horse to a pair of familiar, resident horses in a paddock (PP, 10 minutes, 15 tests), (3) allowing limited physical contact between pairs of horses for a short period of pre-exposure in neighboring boxes (B, 5 minutes, 16 tests) before mixing them in a paddock (BP, 10 minutes 16 tests). A total of 16 Swedish Standardbred mares, aged 6-18 years (mean age ± SD: 11 ± 4.4), were included in the study. Half of the horses were familiar with each other (resident horses, n = 8), whereas the other half were bought in from a variety of sources (unfamiliar horses, n = 8). Social interactions, consisting of behaviors from the sender, the receiver, and the subsequent sender's response, were recorded continuously as frequencies. There were no differences in the frequencies of aggressive behaviors between the 3 mixing methods, including those aggressive behaviors in which physical contact had been attempted (kick, strike). Although resident horses were overall more aggressive (median number of aggressive behaviors per horse, 62; Q1, 36; Q3, 68.5) than unfamiliar horses (median per horse, 4; Q1, 2; Q3, 12.5) during all tests (U = 97, P = 0.003), none of the 62 tests needed to be terminated. Unfamiliar horses did not receive more aggression from resident horses in PP (mean per test ± SD: 5.1 ± 3.1) than in P (mean per test ± SD: 6.4 ± 4.9) (t = 0.63, P = 0.544). However, the behavior “attack” was more frequent in PP (median per test, 2; Q1, 0; Q3, 5) than in P (median per test, 0; Q1, 0; Q3, 1) (U = 282, P = 0.042), and “flee” was more frequent in PP (median per test, 6; Q1, 4; Q3, 8) than in P (median per test, 1; Q1, 0; Q3, 6) (U = 290, P = 0.018). Pre-exposure in boxes did not reduce aggression in BP (median per test, 7; Q1, 4.3; Q3, 11.8) as compared with P (median per test, 6; Q1, 2; Q3, 16) (U = 264, P = 0.767), but during pre-exposure in B tests, horses exchanged more nonaggressive (median per test, 2; Q1, 0.3; Q3, 4) than aggressive (median frequency of aggressive behavior, 0; Q1, 0; Q3, 1) (W = 71, P = 0.013) and mixed interactions (median per test, 0; Q1, 0; Q3, 1) (W = 92, P = 0.016) through the opening. Results suggest mixing an unfamiliar horse with 2 resident horses at the same time instead of one by one may be preferable. In this way, the total aggression received by the unfamiliar horse will potentially be less, even though aggressive interactions may be more intense.

Abstract: In animals, behavioural properties such as aggressive propensity are often consistent over a life span, and they may form part of a behavioural syndrome. We studied how aggressive propensity influences dominance, contest behaviour and growth in the cooperatively breeding cichlid fish Neolamprologus pulcher. We tested whether intrinsic aggressive propensity (1) influences dominance in paired contests, (2) causes different aggression levels in contests with partners matched for aggressive propensity compared to unmatched partners, and how it (3) affects growth rate in groups that were either matched or unmatched for aggressive propensity. Intrinsic aggressive propensity was first scored with a mirror test and classified as high, medium or low. Thereafter we tested fish with either high or low aggressive propensity with partners matched for size and either matched or unmatched for aggressive type in a paired contest for a shelter. We scored dominance, aggression and submission. As predicted, (1) dominance was more clearly established in unmatched than in matched contests and (2) individuals with high aggressive propensity launched more attacks overall than fish with low intrinsic aggressiveness, suggesting a higher propensity to escalate independently of winning or losing the paired contest. However, contrary to expectation, (3) individuals with low aggressiveness grew faster than aggressive ones in unmatched groups, whereas the opposite occurred in matched groups. This suggests that individuals with low aggressive propensity may benefit from conflict evasion, which might allow them to gain dominance in the future owing to larger body size.

Abstract: More than half a century has now elapsed since coalition or alliance formation theory (CAFT) was first developed. During that time, researchers have amassed a vast amount of detailed and high-quality data on coalitions or alliances among primates and other animals. But models have not kept pace, and more relevant theory is needed. In particular, even though CAFT is primarily an exercise in polyadic game theory, game theorists have devoted relatively little attention to questions that motivate field research, and much remains largely unexplored. The state of the art is both a challenge and an opportunity. In this review we describe a variety of game-theoretic and related modelling approaches that have much untapped potential to address the questions that field biologists ask.

Abstract: The ability of horses to habituate to frightening stimuli greatly increases safety in the horse-human relationship. A recent experiment suggested, however, that habituation to frightening visual stimuli is relatively stimulus-specific in horses and that shape and colour are important factors for object generalisation (Christensen et al., 2008). In a series of experiments, we aimed to further explore the ability of horses (n = 30, 1 and 2-year-old mares) to recognise and generalise between objects during habituation. TEST horses (n = 15) were habituated to a complex object, composed of five simple objects of varying shape and colour, whereas CONTROL horses (n = 15) were habituated to the test arena, but not to the complex object. In the first experiment, we investigated whether TEST horses subsequently reacted less to i) simple objects that were previously part of the complex object (i.e. testing for object recognition) and ii) a novel object (new shape and colour, i.e. testing for object generalisation), compared to CONTROLS. In the second experiment we investigated whether TEST horses reacted to a change in object order and object location. Behavioural reactions to the object, latency to eat, total eating time and heart rate were recorded. Compared to CONTROLS, TEST horses reacted significantly less towards objects, which were previously part of the complex object (e.g. mean heart rate; P = 0.006), indicating object recognition. In contrast to our expectations, TEST horses also reacted significantly less towards the novel object (e.g. mean heart rate; P = 0.018), suggesting that they were capable of object generalisation. We also found that TEST horses showed an increase in exploratory behaviour when objects within the complex object changed order and location (both P < 0.001), whereas there was no increase in heart rate, indicating that the horses were not frightened by the changes. The results demonstrate that it is possible to increase object generalisation in horses by habituating them to a range of colours and shapes simultaneously. This knowledge greatly affects the way in which horses may be trained to react calmly towards frightening objects.

Abstract: Operant conditioning and two choice preference tests were used to assess the motivation of horses to be released from straight and from box stalls. The motivations for food, a companion, and release into a paddock were compared when the horses had to work for each commodity at increasing fixed ratios of responses (panel presses) to reward in an equine operant conditioning stall. The motivation for food (mean ± SEM = 258 ± 143) responses was much greater than that for either release (38 ± 32) from a straight stall into a large paddock alone or into a small paddock with another horse (95 ± 41) (P = 0.04). When given a two choice preference test between exercise on a treadmill for 20 min or returning to their box stalls, eight of nine horses chose to return to their stalls. In a two choice preference test six of eight horses in box stalls chose to be released into a paddock alone. Horses were given a series of two choice preference tests to determine how long they preferred to be in a paddock. After 15 min in the paddock the horses were re-tested, but all chose the paddock when released into a paddock with three other horses. They were retested every 15 min until they chose to return to their stalls. They chose to stay out for 35 ± 6 min when other horses were in the paddock but for only 17 ± 2 min when they would be alone. When deprived of stall release for 48 h the horses chose to remain in the paddock with other horses for 54 ± 6 min, but showed no compensatory behavior when they were alone (duration chosen = 16 ± 4 min). These findings indicate that horses are not strongly motivated to exercise alone and will choose not to endure forced exercise on a treadmill. The social context of voluntary exercise is important; horses are willing to stay out of their stalls longer if other horses are present and will show compensatory behavior only if other horses are present. These finding have implications for optimizing turnout time for stalled horses.