Editing Procellariiformes (section)

====Nesting and chick rearing====
[[File:W-tail with chick.jpg|thumb|A semi-precocial [[wedge-tailed shearwater]] chick with guarding parent]]
The majority of procellariiforms nest once a year and do so seasonally.<ref>Brooke, 2004. p. 46</ref> Some tropical shearwaters, like the [[Christmas shearwater]], are able to nest on cycles slightly shorter than a year, and the large [[great albatross]]es (genus ''[[Diomedea]]'') nest in alternate years (if successful). Most temperate and polar species nest over the spring-summer, although some albatrosses and procellariids nest over the winter. In the tropics, some species can be found breeding throughout the year, but most nest in discreet periods. Procellariiforms return to nesting colonies as much as several months before laying, and attend their nest sites regularly before copulation. Prior to laying, females embark on a lengthy pre-laying exodus to build up energy reserves in order to lay the exceptionally large egg. In the stormy petrel{{clarification|reason= Which species of storm petrel?|date=October 2023}}, a very small procellariiform, the egg can be 29 percent of the body weight of the female, while in the grey-faced petrel, the female may spend as much as 80 days feeding out at sea after courtship before laying the egg.<ref name=Teara2>{{cite web |url=http://www.teara.govt.nz/en/petrels/page-1 | title=Petrels: Breeding |publisher=Teara: The Encyclopedia of New Zealand |date=13 July 2012 |access-date=2 March 2013 |author=Wilson, Kerry-Jayne |pages=2}}</ref>

When the female returns and lays, incubation is shared between the sexes, with the male taking the first [[avian incubation|incubation]] stint and the female returning to sea. The duration of individual stints varies from just a few days to as much as several weeks, during which the incubating bird can lose a considerable amount of weight.<ref>Warham, J. (1990) ''The Petrels – Their Ecology and Breeding Systems'' London: Academic Press. {{ISBN|978-0-12-735420-0}}</ref> The incubation period varies from species to species, around 40 days for the smallest storm-petrels but longer for the largest species; for albatrosses it can span 70 to 80 days, which is the longest incubation period of any bird.<ref>Brooke, 2004. p. 67</ref>
[[File:Feeding chick.JPG|thumb|left|A [[Laysan albatross]] feeds its chick. The parent pumps food from a modified foregut, the proventriculus, and the chick catches the meal in its lower mandible.]]

Upon hatching, the chicks are semi-[[precocial]], having open eyes, a dense covering of white or grey [[down feather]]s, and the ability to move around the nesting site. After hatching, the incubating adult remains with the chick for a number of days, a period known as the guard phase. In the case of most burrow-nesting species, this is only until the chick is able to [[thermoregulation|thermoregulate]], usually two or three days. Diving-petrel chicks take longer to thermoregulate and have a longer guard phase than other burrow nesters. However, surface-nesting species, which have to deal with a greater range of weather and to contend with predators like [[skua]]s and [[frigatebird]]s, consequently have a longer guard phase (as long as two weeks in procellariids and three weeks in albatrosses).<ref>Brooke, 2004. p. 75</ref>

The chick is fed by both parents. Chicks are fed on fish, squid, krill, and [[stomach oil]]. Stomach oil is [[oil]] composed of neutral dietary [[lipid]]s that are the residue created by [[digestion]] of the prey items. As an energy source for chicks it has several advantages over undigested prey, its [[calorie|calorific]] value is around 9.6 kcal per gram, which is only slightly lower than the value for [[Diesel fuel|diesel]] oil.<ref name = "stomach"/> This can be a real advantage for species that range over huge distances to provide food for hungry chicks.<ref name=j8/> The oil is also used in defence. All procellariiforms create stomach oil except the diving-petrels.<ref name = "stomach"/>

The chick fledges between two and nine months after hatching, almost twice as long as a gull of the same body mass. The reasons behind the length of time are associated with the distance from the breeding site to food. First, there are few predators at the nesting colonies, therefore there is no pressure to fledge quickly.  Second, the time between feedings is long due to the distance from the nest site that adults forage, thus a chick that had a higher growth rate would stand a better chance of starving to death.<ref name="Double" /> The duration between feedings vary among species and during the stages of development. Small feeds are frequent during the guard phase, but afterward become less frequent. However, each feed can deliver a large amount of energy; both sooty shearwater and mottled petrel chicks have been recorded to double their weight in a single night, probably when fed by both parents.<ref name=Teara2/>