Shearwaters

Puffinus puffinus

Over half the world’s population of the Manx shearwater nest on Pembrokeshire’s islands, with the majority of these (350,000 pairs) nesting on Skomer.

Shearwaters are masters of flight but, like the fulmar, are clumsy on land. Without the fulmar’s defence mechanism, they have to nest in burrows on remote islands with no ground predators. The shearwaters are visitors to the Pembrokeshire islands, usually arriving around late March to early April, although they won’t lay their eggs until early May. It is thought that, after mating, the female will head offshore again for about a fortnight to feed whilst the egg develops. When it is laid, the egg will be a massive 15% of the body weight of the adult. Once the egg has been laid, it will take fifty-one days to incubate, with each parent taking it in turns to sit on the egg whilst the other goes out to feed.

After it has hatched, it will be a further seventy days before the chick is ready to leave. Due to being so vulnerable to predation by the larger gulls, such as the greater black-backed gull, shearwaters are largely nocturnal on land. After heading towards the islands en masse at the end of a day’s fishing, they will raft up just off the islands in their thousands, waiting for darkness to fall. It is only then, under the cover of darkness, that they will brave the flight to their burrow.  At sea the shearwaters feed largely on small fish such as sand eel, sprats and herring, plankton, squid and crustaceans and they can cover hundreds of miles on a fishing trip alone. Late August, when it is time to leave, the shearwaters embark on a massive migration to the waters off the coast of Argentina.