The majority of wintering goose and swan populations in Denmark and the rest of Northwestern Europe
have increased significantly during the last decades. A large proportion of these occur in Denmark
during winter.
Knowledge on these changes is highly relevant for the management of these species since the majority
forage on winter crops. This has led to increasing conflicts with farmers due to the negative impact the
foraging has on production and thereby the economy. The scale of the changes in abundance and the
timely changes during the period of increase has hitherto remained unreported in a systematic and
comparable way.
Here we present status and changes over the last decades in the abundance (midwinter counts) and
distribution (DOFbasen data) of goose and swan winter populations in Denmark.
Midwinter counts are performed all across Denmark every January by involvement of a large number
of volunteer birdwatchers. DOFbasen (www.dofbasen.dk) is the main database for casual bird observations in Denmark and provides the data for a description of the distributional changes in this study.
Despite the unsystematic nature of the data, the very high number of records of birds (presently 2.2
million annually; 28 million in total) from all over the country makes these data highly useful to describe
changes in distribution and phenology in the Danish landscape.