Säsongsförändringar av antalet gråhägrar Ardea cinerea vid Kolut fiskdammar i norra Serbien

Abstract

The number of Grey Herons Ardea cinerea occurring at different times of the year on Kolut fishponds in northern Serbia was monitored between 1998 and 2003. With data pooled over the years, the number of birds occurring in the non-breeding period, August to April, varied significantly between months. The number of overwintering herons was low and then increased significantly to reach a spring peak in March. In April the number decreased before breeding, probably because migrating individuals left the area. In autumn there was an even higher peak in November compared to the spring peak. Significantly more herons occurred in autumn (August to December) than in spring (January to April). There was no significant difference between the spring months in the number of herons while there was significantly more herons occurring in November than in the other autumn months. The number of Grey Herons correlated with the number of Great White Egrets Egretta alba, meaning that also the number of Great White Egrets increased when the number of herons did so.