Skomer Island is separated from the mainland of the Marloes Peninsula by the narrow tidal race of Jack Sound. The main plateau is rather flat and slightly larger than Ramsey, but both islands are surrounded by steep cliffs broken by inlets, sea caves and stacks. The island is owned by the Countryside Council for Wales but leased and managed by the Wildlife Trust West Wales. The island is home to some quarter of a million seabirds, by far the most numerous being some 100,000 pairs of Manx shearwater. One of nature's wonders, these elusive seabirds glide the oceans with effortless ease, returning to the island at night where they nest in burrows. Only on land do they become awkward and ungainly. During the winter months they head down to the South Atlantic, off the coasts of Brazil, Uruguay and even as far as Argentina, returning the next spring to breed again on the island. Puffins, guillemots and razorbills all nest on Skomer in large numbers as well, as do chough and peregrine falcons. It is also home to a unique race of bank voles, the Skomer vole, and has the second largest breeding population of grey seals in Wales, behind Ramsey. Most of Skomer has been scheduled an Ancient Monument by Cadw, and the completeness of the archaeological records make the island exceptional. There are remains of Iron age communities around the edges of the island which indicate a numerous prehistoric population and date the influence of farming back to a similar period to that on Ramsey.