The island of Portland, along with its companion Chesil Beach, make up a peninsula which projects some 8 miles out beyond the Dorset coastline into the English Channel. It is this geographical form which accounts for the incredible diversity of migrant birds that are found on Portland. Flocks of migrating birds use the island as either a last stop off point before flying on to the continent or as their first landfall after crossing the Channel.

Seabirds rarely seen from land can be watched moving up and down the Channel from the unique vantage point of Portland Bill. Several species use the Portland cliffs to stay and nest.

The tidal areas at Ferrybridge and the Fleet provide vital feeding places for shorebirds, some of which will nest on the shingle of Chesil Beach.

The man-made shelter of Portland Harbour is used by large numbers of wintering birds, such as grebes, divers and ducks. Wildfowl of many species also use the sheltered waters of the Fleet in winter.