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Seabirds are specifically adapted to live in the harsh conditions that marine environments entail. Their natural habitat is the sea, either in the air, sitting in the water or diving, only coming to land to breed. This high specialization makes them particularly vulnerable to sea degradation.
Not surprisingly, seabirds are the most threatened group of birds worldwide, even more so than tropical forest birds. Not only they have to face the annoyances and problems inland, such as nesting habitat digression and predation, but also they have to struggle against other factors such as diminished availability of food in the sea, accidental mortality due to fishing, pollution and proliferation of various infrastructures.
About 96% of seabirds are colonial (Coulson, 2001). This characteristic is a great handicap for their reproductive biology. Seabirds exploit all the resources in an environment where the potential for nesting is very limited. Places suitable for reproduction are restricted to islands, cliffs from the continental coastlines and certain areas that are geo-morphologically ideal to protect them from predators.
Therefore, often times breeding sites are located away from the feeding areas, which requires both parents to be involved in the search for food; they both travel long distances for days, weeks or even months (in some species of albatross) while chicks (rarely more than one) are left alone in the nest most of the time. As a result, seabirds need much more time than other bird species to breed, and it involves a very significant effort and energy, and a great deal of vital investment. For that matter, larger species do not breed again until a couple years later at least.
The islands of the Atlantic archipelagos (Salvajes and Desiertas) have a great importance for seabirds when it comes to island systems in the North Atlantic (Macaronesian bio-geographic region). These islands are located very far from the continental land and have no human population. Nowadays, seabirds keep safe from predators such as cats and rats, on which the government does control campaigns regularly. These islands are a "paradise" for shearwaters and petrels, and they are the only place in Europe where animals are in full swing at the colony during the day, when traditionally they were visited only at night to avoid predation.
Salvajes
The Archipelago of Salvaje islands maintains one of the major seabird colonies in the Atlantic. Salvaje Grande island stands out because of its important populations of Cory's Shearwater (Calonectris diomedea), Bulwer's Petrel (Bulweria bulwerii), Little Shearwater (Puffinus assimilis), Madeiran Storm-petrel (Oceanodroma castro) and White-faced Storm-petrel (Pelagodroma marina). No terrestrial vertebrate species are present in Salvaje Pequeña island, and the colony of White-faced Storm-petrels is remarkable.
Desiertas
This is an extremely important breeding place for five of the species of the order Procellariiformes. It is the only reproduction area in Europe of the Fea's Petrel (Pterodroma feae), which is a Macaronesian endemic species that nests on the plateau of Bugio, south of Desierta Grande. There are also large colonies of Bulwer's Petrel (Bulweria bulwerii), Cory's Shearwater (Calonectris diomedea) and Madeiran Storm-petrel (Oceanodroma castro). On a smaller scale, but with the same importance, Little Shearwater (Puffinus assimilis) is also present. The other three islands that make up the archipelago are home grounds for Common Terns (Sterna hirundo) and Yellow-footed Gulls, namely the Atlantic subspecies Larus atlantis michaellis.
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 (Morus bassanus) (Foto: S. Requena/CRAM)
 Shearwaters (C. diomedea) in flight (Photo: A. Lorente/CRAM)
 Shearwater inside the nest. (Photo: C. Carboneras)
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