The Avocet is the only wader that broods in colonies and it prefers to breed in wetlands. The most important breeding sites are therefore Eskilsø, Øksneholm and Lilleø, but if they are disturbed there they will also choose smaller islets such as Elleore and Svaleøen. However, as their young need to mature on proper salt meadows, Avocets swim to the nearest salt meadow with their brood a few days after the eggs have hatched. The Avocets on Elleore and Svaleøen, for example, use the salt meadows around Bløden at Risø to raise their young.

The foxes on Eskilsø have significantly reduced the number of Avocet on the fjord, but when the area north of Selsø became part of the sanctuary and was submerged, a large number of Avocets moved there from the fjord.