Impacts of disturbance on migratory waterfowl



It is well known that disturbance from human activities can cause temporary changes in behaviour and locally affect temporal and spatial distribution of migratory and wintering waterfowl. But it is also known that, to some extent, birds can compensate for disturbance by altering their behaviour or habituating to human activities. Comparatively little is known about how these reactions to disturbance may impact on the large-scale dispersion of waterfowl and, ultimately, on their population dynamics. To be able to answer these questions, a better theoretical framework, based on optimal foraging theory incorporating predation risk, and field experiments are required. Furthermore, we need to study the waterfowl throughout their winter ranges to interpret the overall impacts of disturbance. This paper examines two cases where the impacts of disturbance have been assessed from field experiments. In one study, disturbance effects of shooting were tested by setting up experimental reserves in two Danish coastal wetlands. Over a 5-year period, these became two of the most important staging areas for coastal waterfowl, and the national totals of key species were significantly increased. A national management plan which will establish more than 50 new shooting-free refuges on Danish coastal areas within the next 5 years is likely to boost waterfowl numbers even more. Such retention of birds at more northerly sites on the fiyway should result in a more efficient resource utilization and may positively affect the population dynamics where numbers are affected by winter resources. In a second study, the impacts of disturbance by farmers on spring fattening of Pink-footed Geese Anser brachyrhynchus were analysed. In undisturbed areas in northern Norway, abdominal profiles of the geese increased rapidly, whereas in disturbed sites they did not. Subsequently, geese that had used undisturbed sites reproduced better than geese from disturbed sites.