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.
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