Experimental refuges for migratory waterfowl in Danish wetlands. II. Tests of hunting disturbance effects

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Abstract
1. In most situations that have been studied, the creation of refuge areas for migratory waterfowl has generally increased the number of waterfowl using a site. However, experimental evidence to show that the increases were caused by reduced disturbance and not by confounding factors, e.g. improvement of habitat quality of the sites or general population increases, is generally lacking. 2. In two Danish coastal wetlands, waterfowl hunting was the most critical source of disturbance to autumn‐staging waterfowl (Madsen 1998). To test whether hunting disturbance displaced birds from sites, experimental refuge areas were established, with hunting‐free areas manipulated annually during a 4‐year period, followed by permanent refuge establishments, monitored for a further 4 years. 3. In both areas, experiments showed that quarry geese and dabbling ducks redistributed according to the position of the hunting‐free areas, whereas protected species did not. In quarry geese, there was a 6–8‐fold increase in numbers from before to after the experiments; in quarry dabbling ducks there was a 4–50‐fold increase. Dabbling ducks extended the staging period into the winter. Protected waterfowl as well as goldeneye and coot (both quarry species) did not redistribute; their numbers either fluctuated or increased (2 to > 50 fold). 4. In quarry geese and dabbling ducks, changes in food supplies (of the herbivorous species), intensities of recreational activities outside the refuge areas, weather or overall population sizes could not explain the increases. In protected species, as well as goldeneye and coot, trends in local numbers were in accordance with overall population trends for some species; in others, the rate of increase in local numbers was higher than in overall population size. 5. In both areas, species richness increased from before to after the experiments. This was most pronounced in one of the areas where the refuge included shallow‐watered areas in association with salt marshes. 6. It is concluded that prior to experiments, waterfowl hunting caused a displacement of quarry species, resulting in a species‐poor waterfowl community. Refuge creation is an efficient management tool to improve the conservation value and biodiversity of wetlands of importance to waterfowl.