Sterup, J. & Bregnballe, T. 2021. Danmarks ynglebestand af skarver i 2021. Aarhus Universitet, DCE – Nationalt Center for Miljø og Energi, 40 s. - Teknisk rapport nr. 226
http://dce2.au.dk/pub/TR226.pdf
This report presents the results of the annual count of all apparently occupied Great Cormorant nests in Denmark in 2021. Furthermore, it describes the extent of management measures in the colonies.
In 2021, a total of 31,032 nests were registered in Denmark. This is a decrease of 4.6% compared to 2020. Nevertheless, the population has been rather stable since 2014 with between 30,500 and 33,200 breeding pairs. The current population size is around 20% lower than during 1996-2005, when the population peaked at around 40,000 pairs.
The largest regional population changes were recorded in northern Kattegat, where the number of nests decreased by 700 or 18%, and around Smålandsfarvandet with a decrease of 1,200 nests or 13.5%. In the other regions, nest numbers were relatively stable with changes of up to a few hundred nests.
In total, 83 breeding colonies were found in Denmark in 2021. This is 8 less than the 91 colonies found in 2020, which was the largest number of colonies ever recorded in Denmark. The largest colony in 2021 held 2,428 nests and was located in Stavns Fjord on the island of Samsø. Another seven colonies had more than 1,000 nests.
In many colonies it was observed or presumed, that the Great Cormorants were affected by White-tailed Eagles, e.g. by eagles taking chicks or scaring the breeding cormorants from the nest, whereafter crows and gulls could take eggs or small chicks from the nests. There are few actual observations of such incidents, but in several colonies it is assumed, that occurrence of White-tailed Eagles was the main reason for low breeding success and a delay in the timing of onset of breeding.
The Danish Nature Agency, the Ministry of the Environment, implemented management measures to reduce breeding success in twelve colonies in 2021 and gave permission to private landowners to undertake management in another six colonies. In 2021, a total of 3,999 nests were exposed to management, mainly by preventing the eggs from hatching by spraying them with vegetable oil or by removing the nests. The proportion of nests exposed to management measures was approximately as in 2016-2020, but higher than in 2010-2015.
