Bardsey is a National Nature Reserve and a Site of Special Scientific Interest.
It is a site which is both nationally and internationally important for wildlife. The wide range of special interest includes birds, rare flowering plants, lichens, liverworts and mosses, coastal grassland and heathland, seacliff ledges and marine wildlife. It forms part of several larger sites around the mainland coast and seas of the Llyn Peninsula which are recognised internationally for their outstanding wildlife, in particular their birdlife, seacliff habitats and marine wildlife.
This places a responsibility on the Bardsey Island Trust, as owners, and Natural Resources Wales (NRW), as the government's advisory body on wildlife conservation, to ensure that the island's wildlife interest is protected for the future. The important features of the island's natural history are managed through the island farm which is leased to Gareth Roberts, who also farms at Cwrt farm on the mainland. The farm receives financial support from NRW, without which farming would not be possible on the island
Along the coastal margin, the spring squill makes hazy blue carpets in early spring. It’s followed by dense tufts of thrift and patches of thyme and, later on, the bell heather and ling. The rarer plants include western clover and small adder’s tongue. Amongst the most notable of the plants are the lichens, of which Bardsey has a rich variety of over 350 species.
Atlantic grey seals are to be seen in the rocky bays of the island. A small number breed on Bardsey each year.
The Bardsey Bird and Field Observatory opened in 1953. The island lies in the the spring and autumn migration paths of many birds and is home to the eye-catching choughs and oystercatchers; it is also common to see herons, peregrine falcons, wheatears, warblers and little owls, as well as sea birds such as gannets, razorbills and shags. Recent evidence suggests that puffins may be colonising the island too.
The island is mostly associated, however, with the Manx shearwater - there is a breeding colony of ten to sixteen thousand birds on the island.
The seas around the island, with their forests of strap seaweed, are rich in marine life. In the rock pools you can see anemones, crabs and small fish, and in the deeper waters, filter-feeders such as sponges and sea-squirts cushion the rocks. One offshore species, the yellow star anemone, is more commonly found in the Mediterranean. Risso’s dolphins and harbour porpoises are frequently seen in the waters off the island.