The feeding ecology and distribution of Common Coots Fulica atra are affected by hunting taking place in adjacent areas

摘要

Capsule Birds using a shooting-free area are markedly influenced by close-by shooting.Aims To examine changes in distribution, feeding ecology and food supply of Common Coots before and after the beginning of hunting on adjacent salt marshes.Methods Common Coots were counted and mapped in October and November, i.e. before and after the start of hunting. In both months, activity budgets for the Coots were determined. To quantify the food supply, macrophyte biomass samples and depth measures were taken along four parallel transects in the areas used by the birds for foraging.Results Before the start of hunting in October, 45% of all Coots were observed within 400 m of the hunting area. In November (when hunting had started) the birds redistributed themselves away from the hunting area, reducing the number of birds within 400 m to 5%. Because of this redistribution, Coots were observed in deeper-water areas of the lagoon during November compared to October, and foraging by diving increased significantly from 14 to 35%. The average biomass of submerged macrophytes in the lagoon was 155.01 g dry weight/m(2), which corresponds to a total of 302 250 kg in the whole lagoon. The food requirement of each Coot is 52.3 g/day, which is equivalent to 104 kg/day for the autumn peak number at this lagoon (1989 Coots).Conclusion Hunting disturbance outside the shooting-free area displaced Coots from their preferred feeding grounds inside the reserve, causing their redistribution into sub-optimal habitat at greater water depths where Coot feeding costs were higher. Submerged macrophyte biomass showed that food was abundant in the area and therefore unlikely to be a limiting factor that influenced the redistribution of Coots during the shooting season. We suggest that at this particular site the feeding ecology of Coots could be improved by incorporating an appropriate buffer zone between the protected area and the hunted area. This may be of value not only to Coots, but also for other bird species that exploit shallow water.