Here in Wales there are an estimated 120,000 and 45,000 breeding pairs of Manx shearwater making Skomer and Skokholm island, the largest known concentration of this species in the world.
Last updated: 07 April 2011
Manx shearwater live predominantly out at sea and have long, narrow wings and feet placed far back on their body for efficient flying and swimming.
Despite the scientific name, 'Puffinus puffinus', manx shearwater are completely unrelated to puffins - the only resemblance being that they too are burrow-nesting sea birds.
The word 'manx', meaning from the Isle of Man, originates from a large shearwater colony once found on the Calf of Man - a small island just south of the Isle of Man.
Bardsey Island has between 10-16,000 pairs nest at the height of the breeding season including one ringed bird that is a staggering 50 years old and has probably flown millions of miles during its lifetime.
Manx shearwater are not well suited to land and cannot walk properly. They tend to huffle along on their belly, making them easy prey for great black-backed gulls.
Shearwater travel huge distances during migration and studies on Skokholm and Skomer Island have shown that some of the young travel 6000 - 7000 miles in less than a fortnight, travelling to southern Brazil and Argentina for the winter.
Manx shearwater only return inland to breed which takes place on a few islands off the west coast of the UK, especially Skomer and Skokholm in Wales.
The birds are adapted for life on the wing but do have exceptionally long feet which they use to dig out the underground burrows where they nest.
The female returns in May to lay and egg and then flies off again to feed, leaving the males to incubate the egg.
after that the birds take it in turns with the partner spending up to 8 days away at a time away, feeding out at sea on small fish such as sprat, herring and sardine.
The egg laid in comparison to the bird is huge and up to 15% of the total body weight of the bird.
As the sun sets, thousands of birds return to land, under the cover of darkness and set about trying to locate their mate and burrow.
The birds underground on nests will respond, calling out and somehow they all manage to find each other.
Read a blog about when Springwatch visited Bardsey Island and used specialist infra-red cameras to see the birds in their burrows.
Try one of the walks from Derek's latest walking series on BBC One Wales.
Find out about the wildlife you can find on your doorstep.