From March to November, humans aren't the only ones to visit Bardsey. Each year, thousands of birds pass through on their way to their breeding or wintering grounds.

The Bird Observatory Warden and his team of willing volunteers net and ring up to 8,000 of these birds every year in order to understand their migration patterns. Chiffchaffs, goldcrests and wheatears are usually the first to pass through, followed by sedge and willow warblers, whitethroats and spotted flycatchers.

Not all birds use the island merely to refuel. About 30 species regularly nest here, including ravens, little owls, oystercatchers and the rare chough. Hundreds of sea birds, such as razorbills, guillemots, fulmars and kittiwakes spend the summer nesting on the island's eastern cliffs. The numbers reflect the fact that there are no land predators such as rats or foxes to worry about.

On a dark moonless night an eerie cackling can be heard across the island as 16,000 pairs of manx shearwaters come ashore to lay and incubate their eggs in abandoned rabbit warrens or newly-dug burrows. Wales is home to over half the world's population of these birds, with Skomer and Skokholm also having large numbers.

Each winter and spring these birds fly an amazing 12,000km to and from their wintering grounds in South America. Their physical capabilities are not so strong on land, however, and they shuffle clumsily along the ground on their bellies. If you get the chance to accompany the wardens when they're ringing them, be sure to watch your feet!

Some of Bardsey's inhabitants are more at home in the water than on land. The island is one of the best places in north Wales to see grey seals. In mid summer over 200 can be spotted, sunbathing on the rocks or bobbing about in the sea, and about 15 pups are born each autumn. Their sharp teeth and strong jaws are perfect for breaking the shells of lobsters and crabs which dwell in the waters.

On a boat trip around the island you may also spot bottlenose and Risso's dolphins, and porpoises. Bardsey Island is known in Welsh as Ynys Enlli, which means the "isle of the currents". These currents are responsible for flushing in food-rich waters: the Whale and Dolphin Conservation Society have been carrying out surveys since 1999 to find out which areas are particularly important for feeding and nursing calves.

Go on a photo-tour of the island with Iolo Williams.