|Dyke and Sheep-Grazed Areas|
All the stone dykes have lichens growing on them and can harbour large numbers of invertebrates. Lichens are sensitive to air pollution and their abundance on the island indicates clean air. The invertebrates are an important food source for both resident and migratory birds. A number of species (e.g. Rock Pipit, Pied Wagtail, Wheatear, and Starling) use the nooks and crannies in the dykes to nest in. Migrants are frequently found sheltering in the lee of the dykes in rough weather.
The plants outside the sheep dyke are stunted as a result of exposure and heavy grazing by the North Ronaldsay sheep. The observant walker can see dwarf heather, among other plants. Ringed Plover, Arctic Skua and Arctic Tern in particular use these open areas for breeding. Many other birds, especially waders and gulls, use them for feeding, resting and roosting. Large flocks are often seen during the migration periods.
Shelduck, a hole-nesting species, sometimes make use of abandoned rabbit burrows found here. Fulmars also nest in these areas - the first in 1919, they gradually increased their numbers to over 300 pairs. They are normally a cliff nesting species but successfully nest on the ground here, partly because there are no predators such as rats, stoats or foxes on the island.