Aarhus Universitets segl

No. 259: Denmark's breeding stock of cormorants in 2022

Sterup, J. & Bregnballe, T. 2022. Danmarks ynglebestand af skarver i 2022. Aarhus Universitet, DCE – Nationalt Center for Miljø og Energi, 40 s. - Teknisk rapport nr. 259. http://dce2.au.dk/pub/TR259.pdf

Summary

This report presents the results of the annual count of all apparently occupied Great Cormorant nests in Denmark in 2022. Furthermore, it describes the extent of management measures targeted at the breeding colonies.

In 2022, a total of 30,266 nests were registered in Denmark. This is a decrease of 2.9% compared to 2021. Nevertheless, the population has been rather stable since 2014 with between 30,200 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.

There were large regional differences in the population development from 2021 to 2022. In northern Kattegat there was an increase of 1,365 nests or 42%, while there was a decrease in western Jutland (937 nests or 29%) and around Smålandsfarvandet (939 nests or 12%). 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 2022. This is one less than in 2021. The largest colony in 2022 held 2,687 nests and was located in Stavns Fjord on the island of Samsø. Another six colonies had more than 1,000 nests. For the first time, breeding cormorants were found on two light-houses, both in Kattegat.

In 2022, there was an outbreak of avian influenza in some of the breeding colonies. This is the first time, this is known to have occurred in Danish colonies. Especially three colonies near the island of Møn were affected with more than 700 adults found dead. In many colonies it was observed or presumed, that the Great Cormorants were affected by White-tailed Eagles taking chicks or scaring the breeding cormorants off their nests, allowing crows and gulls to take eggs or small chicks. In several colonies it was assumed, that the 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, Ministry of the Environment, implemented management measures to reduce breeding success in eight colonies in 2022 and gave permission to private landowners to undertake management in another three colonies. In 2022, a total of 4,213 nests were exposed to management, all by preventing the eggs from hatching by spraying them with vegetable oil. The proportion of nests exposed to management measures was similar to 2016-2021, but higher than in 2010-2015.