Behavioural Effects of Persistent Human Disturbance: A Playback Experiment in a Forest Bird

Increasing human presence and activities expose wild animals to persistent disturbances. Disturbed populations often become tolerant towards humans, although the underlying mechanisms are poorly understood. We used playback experiments to manipulate perceived level of human disturbance in great tits (Parus major). In the first year, incubating females remained more often on the nest, and parents during brood care exhibited a lower level of vigilance and tended to have shorter return latencies in the human disturbance treatment than in control treatments, demonstrating an increased tolerance. These differences disappeared in the second year. Tolerance was also influenced by distance to roads and the frequency of nest visits by researchers. These results support that behavioural tolerance can quickly emerge by phenotypic plasticity in natural populations, although other mechanisms may also influence behavioural responses after longer exposure to human disturbances, resulting in a complex set of processes involved in the spread of tolerance.