Both of the Skellig islands are known for their seabird colonies, and together comprise one of the most important seabird sites in Ireland, both fo the population size and for the species diversity. Among the breeding birds are European storm petrel (Hydrobates pelagicus), northern gannet, northern fulmar (Fulmarus glacialis), Manx shearwater (Puffinus puffinus), black-legged kittiwake (Rissa tridactyla), common guillemot (Uria aalge), razorbill (Alca torda) and Atlantic puffin (Fratercula arctica) (with 4,000 or more puffins on Great Skellig alone). Red-billed chough (Pyrrhocorax pyrrhocorax) and peregrine falcon (Falco peregrinus) can also be seen.
The surrounding waters have abundant wildlife with many Grey seal (Halichoerus grypus). Basking shark (Cetorhinus maximus), minke whale (Balaenoptera acutorostrata), dolphin (Delphinidae), beaked whale, and leatherback sea turtle (Dermochelys coriacea) have also been recorded. The islands have many interesting recreational diving sites due to the clear water, an abundance of life, and underwater cliffs down to 60 meters (200 feet).
Both Skellig Islands are breeding grounds for a wide range of sea birds, such as Puffins, Razorbills and Guillemots.
The island is home to thousands of birds. During nesting time in late spring early/summer the air is filled with the raucous calls of the gulls. The puffins can easily be seen plodding their way across the heather to their underground homes.
The Little Skellig lies a little closer to the mainland, and is clearly seen from Skellig Michael. On a clear day in early summer, from Skellig Michael you can see the thousands of sea birds circling and diving.
Little Skellig is home to thousands of Gannets, apparently, exactly 22,000 on the last count. It is the biggest Gannet breeding colony in Northern Europe.
The Small Skellig is also famous, but for its ornithological value rather than as a heritage site. Thousands of seabirds inhabit the island as the high cliffs make ideal nesting and breeding areas. The Small Skellig boasts the second largest colony of Gannets in the world, providing shelter to over 27,000 pairs of these seabirds. Some of the other species that inhabit the island include Puffins, Storm Petrels, and Manx shearwaters.