Editing Procellariiformes (section)

====Breeding colonies====
[[File:Xmas shearwaters roosting.jpg|thumb|220px|[[Christmas shearwater]]s are one of the surface-nesting tropical procellariiforms.]]
All procellariiforms are colonial, predominantly breeding on offshore or oceanic islands. The few species that nest on continents do so in inhospitable environments such as dry deserts or on Antarctica. These colonies can vary from the widely spaced colonies of the giant petrels to the dense 3.6 million-strong colonies of [[Leach's storm petrel]]s.<ref name=j3/> For almost all species the need to breed is the only reason that procellariiforms return to land at all. Some of the larger petrels have to nest on windswept locations as they require wind to take off and forage for food.<ref name="Double" /> Within the colonies, pairs defend usually small [[Territory (animal)|territories]] (the giant petrels and some albatrosses can have very large territories) which is the small area around either the nest or a burrow. Competition between pairs can be intense, as is competition between species, particularly for burrows. Larger species of petrels will even kill the chicks and even adults of smaller species in disputes over burrows.<ref name ="Medeiros"/> Burrows and natural crevices are most commonly used by the smaller species; all the storm petrels and [[diving petrel]]s are cavity nesters, as are many of the [[procellariid]]s. The fulmarine petrels and some tropical [[gadfly petrel]]s and [[shearwater]]s are surface nesters, as are all the albatrosses.<ref>{{cite book |title=Chemical Signals in Vertebrates 10 | publisher=Springer |author1=Cunningham, G.B. |author2=Nevitt, G.A. |year=2005 |pages=403 |editor1=Mason, R.T. |editor2=Lemaster, Michael P. |editor3=Müller-Schwarze, D. | chapter=The Sense of Smell in Procellariiformes |chapter-url=https://books.google.com/books?id=zBZZNiN9_PoC&pg=PA403|isbn=9780387251592 }}</ref>

Procellariiforms show high levels of [[philopatry]], both site fidelity and natal philopatry. Natal philopatry is the tendency of an individual bird to return to its natal colony to breed, often many years after leaving the colony as a chick. This tendency has been shown through [[bird ringing|ringing studies]] and [[mitochondrial DNA]] studies. Birds ringed as chicks have been recaptured close to their original nests, sometimes extremely close; in the Laysan albatross the average distance between hatching site and the site where a bird established its own territory was {{convert|22|m|ft|abbr=on}},<ref>{{cite journal |last1=Fisher |first1=H. I. |year=1976 |title=Some dynamics of a breeding colony of Laysan Albatrosses |url=http://sora.unm.edu/node/129258 |journal=Wilson Bulletin |volume=88 |pages=121–142}}</ref> and a study of [[Cory's shearwater]]s nesting near [[Corsica]] found that nine out of 61 male chicks that returned to breed at their natal colony actually bred in the burrow they were raised in.<ref name=j4/> Mitochondrial DNA provides evidence of restricted [[gene flow]] between different colonies, strongly suggesting philopatry.<ref name=j5/>

The other type of philopatry exhibited is site fidelity, where pairs of birds return to the same nesting site for a number of years. Among the most extreme examples known of this tendency was the fidelity of a ringed northern fulmar that returned to the same nest site for 25 years. The average number of birds returning to the same nest sites is high in all species studied, with around 91 percent for [[Bulwer's petrel]]s,<ref name=j6/> and 85 percent of males and 76 percent of females for Cory's shearwaters (after a successful breeding attempt).<ref>{{cite journal |doi=10.1080/00063659409477193 |last1=Thibault |first1=J.-C. |year=1994 |title=Nest-site tenacity and mate fidelity in relation to breeding success in Cory's Shearwater ''Calonectris diomedea'' |journal=Bird Study |volume=41 |issue=1 |pages=25–28|bibcode=1994BirdS..41...25T }}</ref>