Seabird

While seabirds vary greatly in lifestyle, behaviour and physiology, they often exhibit striking convergent evolution, as the same environmental problems and feeding niches have resulted in similar adaptations.

Seabirds and humans have a long history together: They have provided food to hunters, guided fishermen to fishing stocks, and led sailors to land.

Many species are currently threatened by human activities such as oil spills, nets, climate change and severe weather.

"[3] However, by convention, all of the Sphenisciformes (penguins), all of the Phaethontiformes (tropicbirds), all of the Procellariiformes (albatrosses and petrels), all of the Suliformes (gannets, boobies, frigatebirds, and cormorants) except the darters, one family of the Pelecaniformes (pelicans), and some of the Charadriiformes (gulls, skuas, terns, auks, and skimmers) are classified as seabirds.

The phalaropes are usually included as well, since although they are waders ("shorebirds" in North America), two of the three species (red and red-necked) are oceanic for nine months of the year, crossing the equator to feed pelagically.

Many herons and waders (or shorebirds), such as crab-plovers, are also highly marine, living on the sea's edge (coast), but are also not treated as seabirds.

[9] The tropicbirds (Phaethontiformes) are part of the Eurypygimorphae lineage, which is sister to the Aequornithes;[10] this clade also includes the non-seabird Eurypygiformes (kagu and sunbittern).

[11] Seabirds, by virtue of living in a geologically depositional environment (that is, in the sea where sediments are readily laid down), are well represented in the fossil record.

These were flightless seabirds that could dive in a fashion similar to grebes and loons (using its feet to move underwater),[12] but had beaks filled with sharp teeth.

[14] Flying Cretaceous seabirds do not exceed wingspans of two meters; piscivorous pterosaurs occupied seagoing niches above this size.

[15] While Hesperornis is not thought to have left descendants, the earliest modern seabirds also occurred in the Cretaceous, with a species called Tytthostonyx glauconiticus, which has features suggestive of Procellariiformes and Fregatidae.

[16] As a clade, the Aequornithes either became seabirds in a single transition in the Cretaceous or some lineages such as pelicans and frigatebirds adapted to sea living independently from freshwater-dwelling ancestors.

The Procellariiformes are unusual among birds in having a strong sense of smell, which is used to find widely distributed food in a vast ocean,[22] and help distinguish familiar nest odours from unfamiliar ones.

[28] Seabirds evolved to exploit different food resources in the world's seas and oceans, and to a great extent, their physiology and behaviour have been shaped by their diet.

These evolutionary forces have often caused species in different families and even orders to evolve similar strategies and adaptations to the same problems, leading to remarkable convergent evolution, such as that between auks and penguins.

[29] Many seabirds feed on the ocean's surface, as the action of marine currents often concentrates food such as krill, forage fish, squid, or other prey items within reach of a dipped head.

[31] Another seabird family that does not land while feeding is the skimmer, which has a unique fishing method: flying along the surface with the lower mandible in the water—this shuts automatically when the bill touches something in the water.

Plunge diving allows birds to use the energy from the momentum of the dive to combat natural buoyancy (caused by air trapped in plumage),[39] and thus uses less energy than the dedicated pursuit divers, allowing them to utilise more widely distributed food resources, for example, in impoverished tropical seas.

This life-history strategy has probably evolved both in response to the challenges of living at sea (collecting widely scattered prey items), the frequency of breeding failures due to unfavourable marine conditions, and the relative lack of predation compared to that of land-living birds.

[3] This increases breeding success, provides a place for returning mates to reunite, and reduces the costs of prospecting for a new site.

This tendency, known as philopatry, is so strong that a study of Laysan albatrosses found that the average distance between hatching site and the site where a bird established its own territory was 22 metres (72 ft);[58] another study, this time on Cory's shearwaters nesting near Corsica, found that of nine out of 61 male chicks that returned to breed at their natal colony bred in the burrow they were raised in, and two actually bred with their own mother.

Of these, the trip taken by the Arctic tern is the farthest of any bird, crossing the equator in order to spend the Austral summer in Antarctica.

Some of these species still return to the ocean to feed; for example, the snow petrel, the nests of which have been found 480 kilometres (300 mi) inland on the Antarctic mainland, are unlikely to find anything to eat around their breeding sites.

[77] Discards generally benefit surface feeders, such as gannets and petrels, to the detriment of pursuit divers like penguins and guillemots, which can get entangled in the nets.

[79][80][needs update] Overall, many hundreds of thousands of birds are trapped and killed each year, a source of concern for some of the rarest species (for example, only about 2,000 short-tailed albatrosses are known to still exist).

Introduced goats, cattle, rabbits and other herbivores can create problems, particularly when species need vegetation to protect or shade their young.

One of the Millennium Projects in the UK was the Scottish Seabird Centre, near the important bird sanctuaries on Bass Rock, Fidra and the surrounding islands.

The centre allows visitors to watch live video from the islands as well as learn about the threats the birds face and how we can protect them, and has helped to significantly raise the profile of seabird conservation in the UK.

[106][107][108] This led to the Agreement on the Conservation of Albatrosses and Petrels, a legally binding treaty designed to protect these threatened species, which has been ratified by thirteen countries as of 2021 (Argentina, Australia, Brazil, Chile, Ecuador, France, New Zealand, Norway, Peru, South Africa, Spain, Uruguay, United Kingdom).

Pelicans have long been associated with mercy and altruism because of an early Christian myth that they split open their breast to feed their starving chicks.