NIENHUIS J (2018) Numbers and distribution of domestic geese Anser anser forma domesticus in the province of Groningen, 1999-2005. LIMOSA 91 (2): 79-87.

After domestic geese were added to the list of bird species to be included in monitoring schemes in the Netherlands in 1998/99, their numbers increased with more than 20% annually. The question arises whether this increase was real, or whether it was the result of an increase in the number of locations from which this species was reported. In 1999/2000 and 2005/06 we counted domestic geese in the province of Groningen and surroundings. The count in 1999/2000 was complete. In 2005/06 we mainly focused on collecting data to compare with the counts of 1999/2000. In both periods data collection of this extremely sedentary species was spread out over almost an entire year. A large part of the research area was counted multiple times and the highest number counted per location was used in the analysis. In 1999/2000 and 2005/06 we counted 1816 and 1819 geese respectively. A comparison of locations where in both periods geese had been counted revealed an 18% increase (on average 3.4% annually). Based on this percentage, we estimate 2148 birds to be present across all areas in 2005/06. The increase we observed was much lower than the nation-wide annual increase in the same period (22% annually), as measured by Sovon. Therefore we compared our 1999/2000 counts with the midwinter count from January 2000 organized by Sovon. The latter was carried out in a large number of areas. Despite differences in counting method the number of domestic geese in census areas was either comparable with our own data (32% of areas) or no domestic geese were reported in areas where we did observe geese (67% of areas). Probably part of the observers did not report the domestic geese that were present resulting in 37% lower numbers than our own data suggest. Between 2000 and 2006 the percentage of midwinter census areas that did report domestic geese increased, while our own data show a decrease in the number of flocks in these years. Therefore we suspect that the large annual increase of 22% is the result of an increase in the number of observers over time that started to report domestic geese rather than a realistic population increase.

[pdf only for members] [dutch summary]