page_title: Procellariidae
section_title: Breeding season
hierarchical_section_title: Procellariidae / Biology / Breeding / Breeding season
caption_attribution_description: English: Casuarina equisetifolia (with Pterodroma hypoleuca). Location: Midway Atoll, Sand Island
context_page_description: The family Procellariidae is a group of seabirds that comprises the fulmarine petrels, the gadfly petrels, the prions, and the shearwaters. This family is part of the bird order Procellariiformes, which also includes the albatrosses, the storm petrels, and the diving petrels.
  The procellariids are the most numerous family of tubenoses, and the most diverse. They range in size from the giant petrels, which are almost as large as the albatrosses, to the prions, which are as small as the larger storm petrels. They feed on fish, squid and crustacea, with many also taking fisheries discards and carrion. All species are accomplished long-distance foragers, and many undertake long trans-equatorial migrations. They are colonial breeders, exhibiting long-term mate fidelity and site philopatry. In all species, each pair lays a single egg per breeding season. Their incubation times and chick-rearing periods are exceptionally long compared to other birds.
  Many procellariids have breeding populations of over several million pairs; others number fewer than 200 birds.
context_section_description: Like most seabirds, the majority of procellariids breed once a year. There are exceptions; many individuals of the larger species, such as the white-headed petrel, will skip a breeding season after successfully fledging a chick, and some of the smaller species, such as the Christmas shearwaters, breed on a nine-month schedule. Among those that breed annually, there is considerable variation as to the timing; some species breed in a fixed season while others breed all year round. Climate and the availability of food resources are important influences on the timing of procellariid breeding; species that breed at higher latitudes always breed in the summer as conditions are too harsh in the winter. At lower latitudes many, but not all, species breed continuously. Some species breed seasonally, to avoid competition with other species for burrows, to avoid predation or to take advantage of seasonally abundant food. Others, such as the tropical wedge-tailed shearwater, breed seasonally for reasons unknown. Among the species that exhibit seasonal breeding there can be high levels of synchronization, both of time of arrival at the colony and of lay date.
  Procellariids begin to attend their nesting colony around one month prior to laying. Males will arrive first and attend the colony more frequently than females, partly in order to protect a site or burrow from potential competitors. Prior to laying there is a period known as the pre-laying exodus in which both the male and female are away from the colony, building up reserves in order to lay and undertake the first incubation stint respectively. This pre-laying exodus can vary in length from 9 days (as in the Cape petrel) to around 50 days in Atlantic petrels. All procellariids lay one egg per pair per breeding season, in common with the rest of the Procellariiformes. The egg is large compared to that of other birds, weighing 6–24% of the female's weight. Immediately after laying the female goes back to sea to feed while the male takes over incubation. Incubation duties are shared by both sexes in shifts that vary in length between species, individuals and even the stage of incubation. The longest recorded shift was 29 days by a Murphy's petrel from Henderson Island; the typical length of a gadfly petrel stint is between 13 and 19 days. Fulmarine petrels, shearwaters and prions tend to have shorter stints, averaging between 3 and 13 days. Incubation takes a long time, from 40 days for the smaller species (such as prions) to around 55 days for the larger species. The incubation period is longer if eggs are abandoned temporarily; procellariid eggs are resistant to chilling and can still hatch after being left unattended for a few days.
  After hatching the chick is brooded by a parent until it is large enough to thermoregulate efficiently, and in some cases defend itself from predation. This guard stage lasts a short while for burrow-nesting species (2–3 days) but longer for surface nesting fulmars (around 16–20 days) and giant petrels (20–30 days). After the guard stage both parents feed the chick. In many species the parent's foraging strategy alternates between short trips lasting 1–3 days and longer trips of 5 days. The shorter trips, which are taken over the continental shelf, benefit the chick with faster growth, but longer trips to more productive pelagic feeding grounds are needed for the parents to maintain their own body condition. The meals are composed of both prey items and stomach oil, an energy-rich food that is lighter to carry than undigested prey items. This oil is created in a stomach organ known as a proventriculus from digested prey items, and gives procellariids and other Procellariifromes their distinctive musty smell. Chick development is quite slow for birds, with fledging taking place at around 2 months after hatching for the smaller species and 4 months for the largest species. The chicks of some species are abandoned by the parents; parents of other species continue to bring food to the nesting site after the chick has left. Chicks put on weight quickly a
caption: The chick of a Bonin petrel (Pterodroma hypoleuca) takes almost three months to fledge. This chick has most of its adult plumage but still retains a considerable amount of down.
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