Behavioural Responses of Moulting Barnacle Geese to Experimental Helicopter Noise and a Predator
The response of animals to anthropogenic noise can be aggravated by lack of familiarity with its auditory pattern and also by nervousness characteristic of particular phases of their life cycle. Both conditions apply in the Arctic where human activity is highly localised and field operations, being largely restricted to summer, coincide with the period when animals produce and nurse offspring and, in the case of some birds, are rendered flightless by wing moult. We measured behavioural responses in moulting barnacle geese (Branta leucopsis) in Svalbard to a low flying helicopter and compared these with their responses to the presence of Arctic fox (Vulpes lagopus). The pattern of the responses of the birds was independent of stimulus type but the radius of the effect (response distances) was small (≈50 m) for foxes but large (>3 km) for the helicopter. The geese displayed remarkable auditory discrimination: they responded to the sound of the helicopter at 3.2 km even though engine sound level exceeded background only at ≤2 km from source. We attribute their sensitivity to the fact that fundamental frequencies of calls and absolute auditory sensitivities of Anatidae fall close to the peak noise energy output of small helicopters. The specific instantaneous time and energy costs of the responses observed here were very small. Simple time and energy models indicate that the impact of these natural (fox) and anthropogenic (helicopter) disturbances is likely to depend chiefly on their frequency of occurrence.