Integrated management of invasive Canada geese populations in an international context: a case study

Impact scoring for established non-native birds in Europe has shown Canada goose Branta canadensis L. (CG) to have the highest environmental, economic and social impact. Among the ecological effects are grazing and trampling of reed beds or meadows, as well as bioturbation of oligotrophic fens. Management of CG was mainly performed by egg pricking and hunting. Since 2010, the coordination of these efforts was enhanced and additional moult captures (n=180) were performed on a cross-border scale. These were successful for CG, with over 10.500 birds caught between 2010 and 2014. Reported numbers of CG culled by hunters increased in the same period with over 7000 birds shot per season. The overall impact of the combined management efforts was assessed by annual counts of the geese populations in a fixed sample of counting areas. Trends in the average number of geese per municipality and per year were modeled using gee-GLMs. This showed a significant decrease in the number of Canada and feral goose since the beginning of the project. The modeled decline was in line with the trend in the absolute numbers of CG which showed a 40% reduction since 2010. For the species caught in high numbers, the impact was significant over four years, and related to catch effort. This suggests a link between captures and population numbers. However, this would assume other management efforts to be evenly applied over the area, which was not the case. Research indicates CG can disperse over large distances within Europe, blurring effects of a local action over years. Captures were performed within the EU co-funded Interreg projects Invexo (2010-2012) and RINSE (www.rinse-europe.eu) (2012-2014). Future work will be needed to upscale management and implement adaptive management backed by population models and thorough monitoring. This requires continued investment in prevention, awareness raising and generating public support.