The capercaillie (Tetrao urogallus) is Britain's largest native bird and one of its most critically threatened, with a total Scottish population of fewer than 550 individuals concentrated in the Cairngorms. Human disturbance — particularly from outdoor recreation — is now a primary welfare concern alongside habitat condition.
Capercaillie disturbed at lek sites abandon display and may not return for hours, reducing the time available for successful mating at biologically critical periods. Repeated disturbance across the lekking season accumulates into significant breeding failure. Females disturbed on nests in early incubation abandon eggs, losing the entire breeding attempt. Birds that collide with deer fencing — which is invisible at flight speed — suffer traumatic injuries including broken wings and spinal injuries. The cumulative welfare impact of repeated disturbance across a small, stressed population is measurable in declining reproductive output.