Abstract: Allostasis, the concept of maintaining stability through change, has been proposed as a term and a model to replace the ambiguous term of stress, the concept of adequately or inadequately coping with threatening or unpredictable environmental stimuli. However, both the term allostasis and its underlying model have generated criticism. Here we propose the Reactive Scope Model, an alternate graphical model that builds on the strengths of allostasis and traditional concepts of stress yet addresses many of the criticisms. The basic model proposes divergent effects in four ranges for the concentrations or levels of various physiological mediators involved in responding to stress. (1) Predictive Homeostasis is the range encompassing circadian and seasonal variation — the concentrations/levels needed to respond to predictable environmental changes. (2) Reactive Homeostasis is the range of the mediator needed to respond to unpredictable or threatening environmental changes. Together, Predictive and Reactive Homeostasis comprise the normal reactive scope of the mediator for that individual. Concentrations/levels above the Reactive Homeostasis range is (3) Homeostatic Overload, and concentrations/levels below the Predictive Homeostasis range is (4) Homeostatic Failure. These two ranges represent concentrations/levels with pathological effects and are not compatible with long-term (Homeostatic Overload) or short-term (Homeostatic Failure) health. Wear and tear is the concept that there is a cost to maintaining physiological systems in the Reactive Homeostasis range, so that over time these systems gradually lose their ability to counteract threatening and unpredictable stimuli. Wear and tear can be modeled by a decrease in the threshold between Reactive Homeostasis and Homeostatic Overload, i.e. a decrease in reactive scope. This basic model can then be modified by altering the threshold between Reactive Homeostasis and Homeostatic Overload to help understand how an individual's response to environmental stressors can differ depending upon factors such as prior stressors, dominance status, and early life experience. We illustrate the benefits of the Reactive Scope Model and contrast it with the traditional model and with allostasis in the context of chronic malnutrition, changes in social status, and changes in stress responses due to early life experiences. The Reactive Scope Model, as an extension of allostasis, should be useful to both biomedical researchers studying laboratory animals and humans, as well as ecologists studying stress in free-living animals.

Abstract: Groups of 3-5 homing pigeons individually recognizable by different colours of their plumage were followed by helicopter on their way home. In most cases the animals flew together as a group with frequently changing leadership. Flight formations in terms of leadership were noted every minute. It was examined statistically whether the flight order varies at random or whether there are leading and led birds. In 6 out of 7 experiments with groups of 4-5 pigeons flight order was far from random, one or two pigeons proving to be leaders. In only one experiment leadership did not differ from a random distribution. No correlation could be found between the tendency to lead within a group and homing performance of the single pigeon when released individually.

Abstract: The behaviour of humans around horses is thought to have a substantial impact on how people are perceived in subsequent interactions and many horse trainers give detailed advice on how handlers should behave when initially approaching a loose horse. Here we report on three studies designed to explore the effect of different human approach styles on the behaviour of naïve and experienced horses. In the first study, the change in flight distance (distance at which horses started to avoid an approaching human) of twelve semi-feral Dartmoor ponies, undergoing training to allow handling, was assessed. Over the 10 handling sessions median flight distance decreased significantly (p < 0.001) from 2.38 m to 0.00 m and there was a significant positive shift in the ponies' behaviour following the appearance of the researcher (p = 0.002). In a second study the effect of a direct (vigorous, swinging a lead rope and with eye contact) versus indirect (relaxed, no rope swinging and without eye contact) approach style was assessed on six adult experienced riding horses. The mean flight distance during a direct approach style (6.87 m) was significantly greater than that which occurred during an indirect approach style (2.32 m). Direction of approach was not found to significantly affect flight distance. In a third study, the effect of the rope was removed and a similar method to the second study applied to a group of naïve, feral ponies. The effect of different components of approach style, speed of approach, handler body posture and direction of gaze, which might contribute to observed differences in behavioural responses, were then examined systematically in this population. This revealed no significant difference in mean flight distance between the two approach styles (2.28 m indirect versus 2.37 m direct approach), but ponies were significantly more likely to move off in trot (p = 0.025) and to travel further (p = 0.001) when a direct approach was used. Speed of approach was the most salient factor, with a fast approach increasing both the tendency to move off in trot (p < 0.001) and distance travelled (p < 0.001). Body posture (relaxed or tense) had no effect, while flight distance was significantly greater when the person was looking away (p = 0.045). These results suggest horses may have an important egocentric spatial barrier, which perhaps relates to personal space and triggering of the flight response. Contrary to popular belief, body posture did not appear to be very important in the contexts examined unless accompanied by extraneous aids, while the speed of approach is particularly significant. These results are of important practical relevance in reducing the risk of injury, and the effective management of horses with minimal stress.

Abstract: In the present experiments, the 2-action method was used to determine whether pigeons could learn to imitate a conditional discrimination. Demonstrator pigeons (Columba livia) stepped on a treadle in the presence of 1 light and pecked at the treadle in the presence of another light. Demonstration did not seem to affect acquisition of the conditional discrimination (Experiment 1) but did facilitate its reversal of the conditional discrimination (Experiments 2 and 3). The results suggest that pigeons are not only able to learn a specific behavior by observing another pigeon, but they can also learn under which circumstances to perform that behavior. The results have implications for proposed mechanisms of imitation in animals.