The mechanisms by which group-living animals collectively exploit resources, and the role of individuals in group decisions, are central issues for understanding animal distribution patterns. We investigated the extent to which boldness and shyness affect the distribution of social herbivores across vegetation patches, using sheep as a model species. Using an experimental and a theoretical approach, we show that collective choices emerge through the nonlinear dynamics of interactions between individuals, at both short and long distances. Within a range of parameter values derived from the observation of homogeneous groups of each behavioural type, we propose a simple mechanism whereby the same interaction rules can result in different patterns of distribution across patches for bold and shy individuals. We present a mathematical model based on behavioural rules derived from experiments, in which crowding and conspecific attraction affect the probability of entering or leaving patches. Variation in the strength of social attraction is sufficient to account for differences in spatial distribution across patches. The model predicts that resource fragmentation more strongly affects the distribution patterns of shy groups, and suggests that the presence of both bold and shy individuals within groups would result in more flexible behaviour at the population level.

Red deer Cervus elaphus, even in wilderness areas, are increasingly exposed to disturbance from human recreation as well as hunting, and it has been suggested that both types of disturbance may be perceived as a predation risk. We studied the vigilance behaviour of red deer in the Scottish Highlands, in sites with traditionally high numbers of visitors ('disturbed') and sites with relatively few visitors ('less-disturbed') during the main recreational season (spring and summer), and in their mating grounds during the hunting season (autumn and winter). We carried out direct observations, using scan sampling at 3-minute intervals for 1-hour periods, and recorded the number of animals in each group that were vigilant and their mode of vigilance. During the recreational season, in both the disturbed and less-disturbed sites, data were collected in habitats with different levels of cover (grassland, heather and woodland). The percentage of animals that were vigilant was higher in disturbed than in less-disturbed sites, and higher in disturbed grassland (poor cover) and heather (intermediate cover) than in disturbed woodland (good cover). The majority of the vigilant animals in disturbed heather and woodland habitats and in all the less-disturbed habitats were standing. In disturbed grassland, however, lying was the main posture whilst vigilant. In both disturbed grassland and heather, the percentage of vigilant animals that were moving was higher than in woodland or the less-disturbed habitats. In disturbed sites, the deer were more likely to be aggregated when vigilance levels were high. During the hunting season, the overall level of vigilance was higher than at any sites during the recreational season, and the majority of vigilant animals were moving. We conclude that red deer respond to disturbance from human recreational activities by increasing their level of vigilance, but that the nature of their response varies with the level of cover available. We suggest that red deer may lie down when keeping vigil in grasslands, because lying animals are less conspicuous and the low cover will still allow animals to scan their surroundings. We conclude that, although they respond to both types of disturbance by increasing vigilance, red deer perceive human recreation as a less acute threat than hunting.

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