Life-history

There is also a long period of care for the young, extending for as long as six months, among the longest for birds. For example, once Common Guillemot chicks fledge they remain with the male parent for several months at sea. The frigatebirds have the longest period of parental care of any bird, with the chicks fledging after 4 to 6 months and with continued assistance after that for up to 14 months.Metz, V.G. & Schreiber, E.A. (2002) "Great Frigatebird (Fregata minor)" In The Birds of North America, No 681, (Poole, A. & Gill, F., eds) The Birds of North America Inc:Philadelphia This life-history strategy has probably evolved both in response to the challenges of living at sea and the relative lack of predation compared to that of land living birds.

Because of the greater investment in raising the young and because foraging for food may occur far from the nest site, in most species both parents participate in caring for the young and pairs are typically at least seasonally monogamous. Many species, such as gulls, auks and penguins, retain the same mate for several seasons, and many petrel species mate for life.Brooke, M. (2004). Albatrosses And Petrels Across The World Oxford University Press, Oxford, UK ISBN 0-19-850125-0 The albatrosses and procellariids which mate for life can take many years to form a pair bond before they breed, and the albatrosses have an elaborate breeding dance that is part of pair bond formation.

Seabird colonies

''See also Seabird colony

95% of seabirds are colonial,Schreiber, Elizabeth A. & Burger, Joanne.(2001.) Biology of Marine Birds, Boca Raton:CRC Press, ISBN 0-8493-9882-7 and seabird colonies are amongst the largest in the world, and provide one of Earth's great wildlife spectacles. Colonies of over a million birds have been recorded, both in the tropics (such as Kiritimati in the Pacific) and in the polar latitudes (as found in Antarctica). Seabird colonies occur exclusively for the purpose of breeding, non-breeding birds will only collect together outside the breeding season in areas where prey species are densely aggregated.

Seabird colonies are highly variable. Individual nesting sites can be widely spaced, as in an albatross colony, or densely packed like a murre colony. In most seabird colonies several different species will nest on the same colony, often exhibiting some niche separation. Seabirds can nest in trees (if any are available), on the ground (with or without nests), on cliffs, in burrows under the ground and in rocky crevices. Competition can be strong both within species and between species, with agressive species such as Sooty Terns pushing less dominant species out of the most desirable nesting spaces. The tropical Bonin petrel nests during the winter to avoid competion with the more agressive Wedge-tailed Shearwater, when the seasons overlap the Wedge-tailed Shearwaters will kill young Bonin Petrels in order to use their burrows.Seto, N. W. H., and D. O’Daniel. (1999) Bonin Petrel (Pterodroma hypoleuca). In The Birds of North America, No. 385 (A. Poole and F. Gill, eds.). The Birds of North America, Inc., Philadelphia, PA.

Many seabirds show remarkable site fidelity, returning to the same burrow, nest or site for many years, and they will defend that site from rivals with great vigour. This increases breeding success, provides an place for returning mates to reunite, and reduces the costs of prospecting for a new site. Young adults breeding for the first time usually return to their natal colony, and often nest very close to where they hatched. This tendency, known as philopatry, is so strong that a study of Laysan Albatross found that the average distance between hatching site and the site where a bird established its own territory was 22 metres;Fisher, H.I., (1976) "Some dynamics of a breeding colony of Laysan Albatrosses. Wilson Bulletin 88: 121-142. 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.Rabouam, C., Thibault, J.-C., Bretagnole, V., (1998) "Natal Philopatry and Close Inbreeding in Cory's Shearwater (Calonectris diomedea)" Auk 115(2): 483-486 ^*

Colonies are thought to provide protection to seabirds, which are often very clumsy on land, and are usually situated on islands where land mammals have difficulty getting to. Coloniality often arises in other types of bird which do not defend feeding territories (such as swifts, which have a very variable prey source), this may be a reason why it arises more frequently in seabirds. There are other possible advantages, colonies may act as information centres, where seabirds returning to the sea to forage can find out where prey is by studying returning individuals of the same species There are disadvantages to colonial life, particularly the spread of disease. Colonies also attract the attention of predators, principally other birds, and many species attend their colonies nocturnally to avoid predation. Keitt, B.S., Tershy, B.R. & Croll, D.A (2004). "Nocturnal behavior reduces predation pressure on Black-vented Shearwaters Puffinus opisthomelas" Marine Ornithology 32 (3): 173-178.^*

Seabird migration

Other species also migrate shorter distances away from the breeding sites, their distribution at sea determined by the availability of food. After fledging, juvenile birds often disperse further than adults to, and to different areas, and are commonly sighted far from a species' normal range. Some species, such as the auks, do not have a concerted migration effort, but drift southwards as the winter approaches. Other species, such as some of the storm-petrels, diving petrels and cormorants, never disperse at all, staying near the breeding colonies year round.

Away from the sea

The more marine species, such as petrels, auks, and gannets, are more restricted in their habits, but are occasionally seen inland as vagrants. This most commonly happens to young inexperienced birds, but can happen in large numbers to exhausted adults after a large storm, an event known as a wreck, where they are prized sightings for birders.

Seabirds and humans

Seabirds and fisheries

Fishermen have long used seabirds as indicators of both fish shoals, Au, D.W.K. & Pitman, R.L. (1986) Seabird interactions with Dolphins and Tuna in the Eastern Tropical Pacific. Condor, 88: 304-317. ^* underwater banks that might indicate fish stocks, and of potential land. In fact the known association of seabirds with land was instrumental in allowing the Polynesians to locate tiny landmasses in the Pacific.Schreiber, Elizabeth A. & Burger, Joanne.(2001.) Biology of Marine Birds, Boca Raton:CRC Press, ISBN 0-8493-9882-7 Seabirds also provided food for fishermen away from home, as well as bait. Famously tethered cormorants have been used to catch fish directly. Indirectly fisheries have also benefited from guano from colonies of seabirds acting as fertilizer for the surrounding seas.

Negative effects on fisheries are mostly restricted to raiding by birds on aquaculture, although longlining fisheries also have to deal with bait-stealing. There have been claims of prey-depletion by seabirds of fishery stocks, and while there is some small evidence of this, the effects of seabirds are considered smaller than that of marine mammals and predatory fish (like tuna).

Some species and families of seabirds have benefited from fisheries, particularly from discarded fish and offal. These discards comprise 30% of the food of seabirds in the North Sea, for example, and comprise up to 70% of the total food of some species. This can have other impacts, for example the spread of the Northern Fulmar through the British Isles is attributed in part to the availability of discards.Thompson, P.M., (2004) "Identifying drivers of change; did fisheries play a role in the spread of North Atlantic fulmars?" in Management of marine ecosystems: monitoring change in upper trophic levels. Cambridge: Cambridge University Press ^* Discards generally benefit surface feeders, such as gannets and petrels to the detriment of pursuit divers like penguins.

Fisheries also have negative effects on seabirds, and these effects, particularly on the long lived and slow breeding albatross are a source of increasing concern to conservationists. The by-catch of seabirds entangled in nets or hooked on fishing lines has had a big impact on seabird numbers, for example an estimated 100,000 albatross are hooked and drown each year on tuna lines set out by long-line fisheries.BirdLife International/RSPB (2005) Save the Albatross: The Problem Retrieved March 17, 2006 Brothers NP. 1991. "Albatross mortality and associated bait loss in the Japanese longline fishery in the southern ocean." Biological Conservation 55: 255-268. Overall many hundreds of thousands or possibly millions of birds are trapped and killed each year, a source of concern for some of the rarest species (for example, only 1,000 Short-tailed Albatross are known to still exist). Seabirds also suffer when stocks of fish are overfished.

Exploitation of seabirds

Both hunting and egging continue today, although not at the level that occurred in the past, and generally in a more controlled level. For example, the Māori of Stewart Island/Rakiura continue to harvest the chicks of the Sooty Shearwater as they have done so for centuries, using traditional methods (called kaitiakitanga) to manage the harvest, but now also work with the University of Otago in studying the populations. In Greenland, however, uncontrolled hunting is pushing many species into steep decline.Burnham, W., Burnham, K.K., Cade, T.J., (2005) "Past and present assessments of bird life in Uummannaq District, West Greenland" Dansk Orn. Foren. Tidsskr. 99: 196-208 ^*

Other threats

The build up of toxins and pollutants in seabirds is also a concern. Seabirds, being apex predators, suffered from the ravages of DDT until they were banned, and concern continues with other pollutants, for example Forster's Terns in San Francisco were found to have high levels of polybrominated diphenyl ethers (PBDEs), used as fire retardants. Oil spills are also a major threat to seabird species, as both a toxin and because the feathers of the birds become saturated by the oil, causing them to lose their waterproofing.

Seabird conservation

The field of island restoration, developed initially by New Zealand, is removing exotic invaders from increasingly large islands. Feral cats have been removed from Ascension Island, Arctic Foxes from many islands in the Aleutians, Williams, J.C., Byrd G.V.& Konyukhov, N.B. (2003) Whiskered Auklets Aethia pygmaea, foxes, humans and how to right a wrong. 'Marine Ornithology 31: 175-180 ^* and rats from Campbell Island. The removal of these introduced species has led to increases in surviving species and even the return of expirated ones. After the removal of cats from Ascension Island seabirds began to nest there again for the first time in over a hundred years.

Seabird mortality caused by long-line fisheries can be massively reduced by techniques such as setting long-line bait at night, dying the bait blue, setting the bait underwater, increasing the amount of weight on lines and using bird scarers can all reduce the seabird by-catch,Food and Agriculture Organisation (1999) "The incidental catch of seabirds by longline fisheries: worldwide review and technical guidelines for mitigation. FAO Fisheries Circular No.937. Food and Agriculture Organization of the United Nations, Rome. ^* and their deployment is increasingly required by many national fishing fleets. The international ban on the use of drift nets has also helped reduce the mortality of seabirds and other marine wildlife.

One of the Millennium Projects in the UK was the Scottish Seabird Centre, near the important bird sanctuaries on Bass Rock, Fidra and other surrounding islands. The area is home to huge colonies of gannets, puffins, skuas and other seabirds. 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.

The plight of albatross and other large seabirds, as well as other marine creatures, being taken as by-catch by longline fisheries, has been taken up by a large number of NGOs (including BirdLife International and the RSPB). This lead to Agreement on the Conservation of Albatrosses and Petrels signed as part of the Convention on Migratory Species, a legally binding treaty designed to protect these threatened species (it has currently been ratified by eight countries, Argentina, Australia, Ecuador, New Zealand, Spain, France, Peru and South Africa.

Seabirds in culture