Lilleø is the biggest of the Jyllinge Holme islands. The eastern part consists of an 8 metre high crest, while the western part is low salt meadow, reminiscent of the other islands. Sheep and geese graze here in summer. In the past there have also been cows, horses and goats here. The goats were not a good thing, as they ate everything, including birds’ nests.
Lilleø has a rich bird life, including, notably, a wide range of waders and large colonies of both Arctic Tern and Common Tern. Up to a dozen pairs of Little Tern have bred here for several years.
Beside the plant species found on the other islands off Jyllinge, Lilleø also has the vegetation typical of open, grazed land, and this is maintained by sheep grazing on the hill.
Between Lilleø and Old Jyllinge is a narrow boating channel which is kept free of ice by the current in winter. There are often a great many water birds in this opening in the ice, and it is possible to get very close to the birds when the hunters’ association feeds them.
The ban on landing during the birds’ breeding season does not apply to Lilleø, as it is necessary to care for the animals. Fortunately traffic on the island is mainly restricted to this activity.