Editing Seabird (section)

=== Breeding and colonies ===
{{See also|Bird colony|Seabird breeding behavior}}

[[File:Murre colony.jpg|thumb|right|[[Common murre|Common murres]] breed on densely packed colonies on offshore rocks, islands and cliffs.]]
Ninety-five percent of seabirds are colonial,<ref name="Burger" /> and seabird colonies are among the largest bird colonies in the world, providing 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 Ocean|Pacific]]) and in the polar latitudes (as 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.<ref>{{Citation |last1=Kharitonov |first1=Sergei P. |title=Colony Formation in Seabirds |date=1988 |work=Current Ornithology |pages=223–272 |editor-last=Johnston |editor-first=Richard F. |url=https://doi.org/10.1007/978-1-4615-6787-5_5 |access-date=2024-04-19 |place=Boston, MA |publisher=Springer US |language=en |doi=10.1007/978-1-4615-6787-5_5 |isbn=978-1-4615-6787-5 |last2=Siegel-Causey |first2=Douglas}}</ref>

Seabird colonies are highly variable. Individual nesting sites can be widely spaced, as in an albatross colony, or densely packed as with a [[murre]] colony. In most seabird colonies, several different species will nest on the same colony, often exhibiting some [[Niche differentiation|niche separation]]. Seabirds can nest in trees (if any are available), on the ground (with or without [[bird nest|nests]]), on cliffs, in [[burrow]]s under the ground and in rocky crevices. Competition can be strong both within species and between species, with aggressive species such as [[sooty tern]]s pushing less dominant species out of the most desirable nesting spaces.<ref>Schreiber, E. A., Feare, C. J., Harrington, B. A., Murray, B. G., Jr., Robertson, W. B., Jr., Robertson, M. J. and Woolfenden, G. E. (2002). Sooty Tern (''Sterna fuscata''). In ''The Birds of North America'', No. '''665''' (A. Poole and F. Gill, eds.). The Birds of North America, Inc., Philadelphia, PA</ref> The tropical [[Bonin petrel]] nests during the winter to avoid competition with the more aggressive [[wedge-tailed shearwater]]. When the seasons overlap, the wedge-tailed shearwaters will kill young Bonin petrels in order to use their burrows.<ref>Seto, N. W. H. and O'Daniel, D. (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</ref>

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.<ref name="Burger" /> This increases breeding success, provides a place for returning mates to reunite, and reduces the costs of prospecting for a new site.<ref>{{cite journal|author1=Bried, J. L. |author2=Pontier, D. |author3=Jouventin, P. |year=2003|title=Mate fidelity in monogamous birds: a re-examination of the Procellariiformes|journal=Animal Behaviour |volume=65|pages= 235–246|doi=10.1006/anbe.2002.2045|s2cid=53169037 }}</ref> Young adults breeding for the first time usually return to their natal colony, and often nest close to where they hatched. This tendency, known as [[philopatry]], is so strong that a study of [[Laysan albatross]]es found that the average distance between hatching site and the site where a bird established its own territory was {{convert|22|m|ft}};<ref>{{cite journal|author=Fisher, H. I. |year=1976|title=Some dynamics of a breeding colony of Laysan Albatrosses|url=http://sora.unm.edu/node/129258|jstor=4160718|journal=Wilson Bulletin |volume=88|issue=1|pages= 121–142}}</ref> another study, this time on [[Cory's shearwater]]s 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.<ref>{{cite journal|author1=Rabouam, C. |author2=Thibault, J.-C. |author3=Bretagnole, V. |year=1998|title=Natal Philopatry and close inbreeding in Cory's shearwater (''Calonectris diomedea'')|journal=Auk |volume=115 |issue=2 |pages= 483–486 |url=http://sora.unm.edu/sites/default/files/journals/auk/v115n02/p0483-p0486.pdf|doi=10.2307/4089209|jstor=4089209 }}</ref>

Colonies are usually situated on islands, cliffs or headlands, which land mammals have difficulty accessing.<ref name ="Moors">Moors, P. J.; Atkinson, I. A. E. (1984). ''Predation on seabirds by introduced animals, and factors affecting its severity''. In ''Status and Conservation of the World's Seabirds''. Cambridge: ICBP. {{ISBN|0-946888-03-5}}</ref> This is thought to provide protection to seabirds, which are often very clumsy on land. Coloniality often arises in types of birds that do not defend feeding territories (such as [[Swift (bird)|swift]]s, which have a very variable prey source); this may be a reason why it arises more frequently in seabirds.<ref name="Burger" /> 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 [[predation|predators]], principally other birds, and many species attend their colonies nocturnally to avoid predation.<ref>{{cite journal|author1=Keitt, B. S. |author2=Tershy, B. R. |author3=Croll, D. A. |year=2004|title=Nocturnal behavior reduces predation pressure on Black-vented Shearwaters ''Puffinus opisthomelas''|journal=Marine Ornithology |volume=32|issue=3 |pages= 173–178|url=http://www.marineornithology.org/PDF/32_2/32_2_173-178.pdf}}</ref> Birds from different colonies often forage in different areas to avoid competition.<ref>{{Cite journal|last1=Bolton|first1=Mark|last2=Conolly|first2=Georgia|last3=Carroll|first3=Matthew|last4=Wakefield|first4=Ewan D.|last5=Caldow|first5=Richard|date=2019|title=A review of the occurrence of inter-colony segregation of seabird foraging areas and the implications for marine environmental impact assessment|journal=Ibis|language=en|volume=161|issue=2|pages=241–259|doi=10.1111/ibi.12677|issn=1474-919X|doi-access=free}}</ref>