How has the risk of predation shaped the behavioural responses of sheep to fear and distress?
To use behaviours as indicators of stress it is important to understand their underlying causation. For a prey animal in the wild, such as a sheep, behavioural responses have evolved to evade detection and capture by predators. The behavioural responses of the wild ancestors of domestic
sheep to the threat of predation are characterised predominantly by vigilance, flocking, flight to cover and behavioural inhibition once refuge has been reached. Some limited defensive behaviours are seen, mainly in females with young against small predators. Vigilance and flight distance
are affected by the animal's assessment of risk and are influenced by the environment, social group size, age, sex and reproductive condition, as well as by previous experience with potential predators. Under conditions of stress, domestic sheep show similar behavioural reactions to wild sheep,
although the threshold at which they are elicited may be elevated. This is particularly evident when comparing less selected hill breeds with more highly selected lowland breeds, and suggests that a continuum of responsiveness exists between wild and feral sheep, through hill breeds to the
lowland sheep breeds. However, this may be confounded by the previous experience of the breeds, particularly their familiarity with humans. Behavioural and neurobiological evidence suggests that, although the behavioural response to predators (vigilance, flight) is innate, the stimuli that
elicit this behavioural pattern may have a learned component. Since vigilance and flight distances are affected by the animal's perception of threat, they may be useful indices of stress in sheep and, as graded responses, give some indication of the level of threat experienced by the sheep.
Thus they may indicate the amount of fear or distress experienced by the sheep and hence have the potential to be used in the assessment of welfare states.