In excess of 170,000 birds inhabit Fowlsheugh at the peak breeding season between April and late July. This value places Fowlsheugh as the second largest seabird colony in Britain and surpasses the criterion of 20,000 birds to qualify as a protected area of international seabird importance under European Union Directive 79/409. Bird species present are primarily auks and gulls, which feed in nearby offshore waters as well as more distant North Sea reaches. Most of the nests are constructed on precarious perches nestled in the virtually vertical cliffs of the basalt and conglomerate. During breeding season the bluffs are dense in birds arriving, departing and feeding in the waters below. Sound levels from birds have been measured as high as 69 dBA for a one-hour interval.