Research Notes from NERI no. 220: Cormorants 2005. Eskildsen, J. Natur-Inform. 2005. 48 pp.

 

Summary

In 2005, the total number of cormorant nests counted in Denmark was 39,720 distributed between 56 colonies. This number is very close to that counted in 2004 and the population is regarded as stable, not only from 2004 to 2005 but also seen in relation to surveys during the last 10 years. During 1995-2005 the number of nests has averaged 39,560 (range 36,700 to 42,800).

The trends amongst the colonies have differed between regions. In West Jutland and in Limfjorden the number of nests has decreased by 1,250, while the number in the Kattegat region has increased correspondingly. The populations in southern waters have been stable from 2004 to 2005. The reasons for the differences between West Jutland and Kattegat may be due to differences in the availability of food resources, possibly in combination with destruction of nests by nature management authorities in a number of colonies in West Jutland.

Nearly 5,000 cormorant nests were destroyed in 2005 corresponding to 12% of the total number of nests. Destruction of nests decreased by 25% compared to 2004 and the control measures have been concentrated at colonies in West Jutland and around Læsø. Nest destruction was carried out at 15 colonies corresponding to 27% of all colonies in Denmark. 96% of the destroyed nests were sprayed, i.e. eggs were sprayed with a fluid that seals the gas-permeable pores in the eggshells and consequently kills the embryo. It is concluded that spraying reduces breeding success and at the same time it will prevent cormorants from sprayed nests from establishing new colonies.

The number of cormorant nests in Denmark during the last 10 years can be regarded as a stable, indicating a stable breeding population with natural fluctuations due to influence from the surrounding environment, primarily the availability of food resources.

 

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