Procellariiformes is an order of seabirds that comprises four families: the albatrosses, procellariids, storm-petrels and diving petrels. Formerly called Tubinares and still called tubenoses in English, they are often referred to collectively as the petrels, a term that has been applied to all Procellariiformes or more commonly all the families except the albatrosses. They are almost exclusively pelagic (feeding in the open ocean). They have a cosmopolitan distribution across the world's oceans, with the highest diversity being around New Zealand.
Procellariiformes are colonial, mostly nesting on remote predator-free islands. The larger species nest on the surface, while most smaller species nest in natural cavities and burrows. They exhibit strong philopatry, returning to their natal colony to breed and returning to the same nesting site over many years. Procellariiformes are monogamous and form long-term pair bonds which are formed over several years and may last for the life of the pair. Only a single egg is laid per nesting attempt, and usually only a single nesting attempt is made per year, although the larger albatrosses may only nest once every two years. Both parents participate in incubation and chick rearing. Incubation times are long compared to other birds, as are fledgling periods. Once a chick has fledged there is no further parental care.
Procellariiformes have had a long relationship with humans. They have been important food sources for many people, and continue to be hunted as such in some parts of the world. They have also been the subject of numerous cultural depictions, particularly albatrosses. Procellariiformes are one of the most endangered bird taxa, with many species threatened with extinction due to introduced predators in their breeding colonies, marine pollution and the danger of fisheries by-catch. Scientists, conservationists, fishermen and governments around the world are working to reduce the threats posed to them, and these efforts have led to the signing of the Agreement on the Conservation of Albatrosses and Petrels, a legally binding international treaty signed in 2001.
The storm-petrels are almost as widespread as the procellariids, and fall into two distinct subfamilies; the Oceanitinae have a mostly southern hemisphere distribution and the Hydrobatinae are found mostly in the northern hemisphere. Amongst the albatrosses the majority of the family is restricted to the southern hemisphere, feeding and nesting in cool temperate areas, although one genus, Phoebastria, ranges across the north Pacific. The family is absent from the north Atlantic, although fossil records indicate they bred there once. Finally the diving-petrels are restricted to the southern hemisphere.
The various species within the order have a variety of migration strategies. Some species undertake regular trans-equatorial migrations, such as the Sooty Shearwater which annually migrates from its breeding grounds in New Zealand and Chile to the North Pacific off Japan, Alaska and California, an annual round trip of 64,000 km (40,000 miless), the longest measured annual migration of any bird. A number of otherpetrel species undertake trans-equatorial migrations, including the Wilson's Storm-petrel and the Providence Petrel, but no albatrosses cross do due to their reliance on wind assisted flight. There are other long-distant migrants within the order; Swinhoe's Storm-petrels breed in the western Pacific and migrates to the western Indian Ocean, and Bonin Petrels nesting in Hawaii migrate to the coast of Japan during the non-breeding season.
Procellariiformes range in size from the very large Wandering Albatross, at 10 kg, to the tiny Least Storm-petrel, at 20 g. They have their nostrils enclosed in one or two tubes on their straight, deeply grooved bills with hooked tips. The beaks are made up from several plates. Wings are long and narrow; feet are webbed, and the hind toe is undeveloped or non-existent. Plumage is predominantly black, white and grey.
The order has a characteristic tubular nasal passage which is used for olfaction. This ability to smell helps to locate patchily distributed prey at sea and may also help locate their nests within nesting colonies.
The longer-winged species fly using a switchback technique to minimise active flapping. All eat fish, squid or similar marine prey.
Most are unable to walk well on land, and many species visit their remote breeding islands only at night. The exceptions are the huge albatrosses, several of the gadfly petrels and shearwaters and the fulmar-petrels. The latter can disable even large predatory birds with their obnoxious stomach oil, which they can project some distance. This stomach oil is a digestive residue created in the foregut of all tubenoses except the diving petrels, and is used mainly for storage of energy rich food as well as for defence.
All Procellariiformes 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 Petrels. For almost all species the need to breed is the only reason that Procellariiformes return to land at all. Within the colonies pairs defend usually small territories (the giant petrels and some albatrosses can have very large territories) which is either the small area around the nest or a burrow. Competition between pairs can be intense, as can 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. Burrows and natural crevices are most commonly used by the smaller species; all the storm-petrels and diving-petrels are cavity nesters, as are many of the procellariids. The fulmarine petrels and some tropical gadfly petrels and shearwaters are surface nesters, as are all the albatrosses. Colonies are often composed of several different species of both petrels and other seabirds.
Procellariiformes 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 ringing studies and mitochondrial DNA studies. In the ringing studies birds ringed as chicks are recapatured close to their original nests, a tendency which can be extreme at times; in Laysan Albatross the average distance between hatching site and the site where a bird established its own territory was 22 metres, and a study of Cory's Shearwaters nesting near Corsica found that of nine out of 61 male chicks that returned to breed at their natal colony actually bred in the burrow they were raised in. Mitochondrial DNA provides evidence of restricted gene flow between different colonies, strongly suggesting philopatry.
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 which returned to the same site for 25 years. The average number of birds returning to the same nesting sites is high in all species studied, with figures of around 91% for Bulwer's Petrels, and 85% of males and 76% of females for Cory's Shearwaters (after a successful breeding attempt).
Procellariiformes are monogamous breeders and form long term pair-bonds. These pair bonds take several years to develop in some species, particularly with the albatrosses. Having formed they will last for many breeding seasons, in some cases for the life of the pair. Petrel courtship can be an elaborate affair. It reaches its extreme with the albatrosses, where pairs of albatrosses spend many years perfecting and elaborate mating dances. These dances are composed of synchronised performances of various actions such as preening, pointing, calling, bill clacking, staring, and combinations of such behaviours (like the sky-call). Each particular pair will develop their own individual version of the dance. The breeding behaviour of other Procellariiformes are less elaborate, although similar bonding behaviours are involved, particularly for the surface nesting procellariids. These can involve synchronised flights, mutual preening and calling. Calls are important for helping birds locate potential mates and distinguish between species and may also serve a function in helping individuals assess the quality of potential mates. After pair formation has occurred calls also serve to help them reunite, the ability of individuals to recognise their own mate has also been demonstrated in several species.
Procellariiformes are k-selected. Breeding is delayed for several years after fledging, sometimes for as long as eight or ten years in the case of larger species. Once they begin breeding they make only a single breeding attempt per nesting season, even if the egg is lost early on in the season they will seldom relay. Large amounts of effort are placed into laying a single (proportionally) large egg and raising a single chick. Procellariiformes are long-lived, the longest living albatross known survived for 51 years but was probably older, even the tiny storm-petrels are known to have survived for 30 years.
The majority of Procellariiformes nest once a year and do so seasonally. Some tropical shearwaters, like the Christmas Shearwater, are able to nest on cycles slightly shorter than a year, and the large great albatrosses (genus Diomedea) nest in consecutive years. Most temperate and polar species nest over the spring-summer, although some albatrosses and procellariids nest over the winter. In the tropics some species breed throughout the year, but most nest in discreet periods. Procellariiformes return to the nesting colonies several months before laying, and attend their nesting sites regularly before copulation. Prior to laying females embark on a pre-laying exodus to build up reserves of energy to lay the comparably large egg.
When the female returns and lays the male takes the first incubation stint and the female returns to sea. Incubation is shared between both sexes. The duration of individual stints varies from just a few days to several weeks, during which the incubating bird can lose a considerable amount of weight. 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 be as long as 70 to 80 days, which is the longest incubation period of any bird.
Upon hatching the chicks are semi-precocial, having open eyes, a dense covering of white or grey down feathers, 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 thermoregulate, usually two or three days. Diving-petrel chicks take longer to thermoregulate and have a longer guard phase than other burrow nesters. However, for surface nesting species, which have to deal with a greater range of weather and also have to content with predators like skuas and frigatebirds, and consequently have longer guard phases, as long as two weeks in procellariids and three weeks in albatrosses.
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 lipids 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 calorific value is around 9.6 kcal per gram, which is only slightly lower than the value for diesel oil. This can be a real advantage for species that range over huge distances to provide food for hungry chicks. The oil is also used in defence. All Procellariiformes create stomach oil except the diving-petrels.
The durations between feedings vary between species and during the stages of development. Small feeds are frequent during the guard phase, but afterwards become less frequent.
The albatrosses and petrels are "amongst the most severely threatened taxa worldwide". They face a variety of threats, the severity of which varies greatly from species to species. Several species are amongst the most common of seabirds, including the Wilson's Storm Petrel (an estimated 20 million individuals) and the Short-tailed Shearwater (an estimated 30 million individuals); while the total population of some other species barely reaches more than two hundred individuals. There are less than 200 Magenta Petrels breeding on the Chatham Islands, only 400 Zino's Petrels and only 80 Amsterdam Albatrosses. Only one species is thought to have gone extinct since 1600, the Guadalupe Storm-petrel of Mexico, although a number of species went extinct prior to this. Numerous species are very poorly known, the Fiji Petrel has only been seen a handful of times since its discovery and the breeding colonies of the New Zealand Storm-petrel, Hornby's Storm-petrel and Heinroth's Shearwater have never been located. So little is known about the New Zealand Storm-petrel that is was thought to be extinct for 150 years until its rediscovery in 2003, although this record is dwarfed by that of the Bermuda Petrel which was considered extinct for 330 years.
The principal threat to the albatrosses and larger species of procellariids is long-line fishing. Bait set on hooks is attractive to foraging birds and many are hooked by the lines as they are set. As many as 100,000 albatrosses are hooked and drown each year on tuna lines set out by long-line fisheries. This has led to spectacular declines in some species, as Procellariiformes are slow breeders and cannot replace their numbers fast enough.
Exotic species introduced to the remote breeding colonies is also a threat to all types of Procellariiformes. These principally take the form of predators; most albatross and petrel species are clumsy on land and are unable to defend themselves from mammals such as rats, feral cats and pigs. This phenomenon, known as ecological naivete, has resulted in numerous declines in many species and has been strongly implicated in the extinction of the Guadalupe Storm-petrel. Introduced herbivores can also cause problems if they unbalance the ecology of the island; introduced rabbits destroyed the forest understory on Cabbage Tree Island off New South Wales; this both increased the vulnerability of the Gould's Petrels nesting on the island to natural predators and left them vulnerable to the sticky fruits of the birdlime tree (Pisonia umbellifera), a native plant. In the natural state these fruits lodge in the understory of the forest, but with the understory removed the fruits fall to the ground where the petrels move about, sticking to their feathers and making flight impossible.
In the past exploitation was a threat (see above), although this is less of a threat now. Other threats the ingestion of plastic flotsam. Once swallowed, this plastic can cause a general decline in the fitness of the bird, or in some cases lodge in the gut and cause a blockage, leading to death by starvation. This can also be picked up by foraging adults and fed to chicks, stunting their development and reducing the chances of successfully fledging. Procellariids are also vulnerable to general marine pollution, as well as oil spills. Some species, such as the Barau's Petrel and the Newell's Shearwater, which nest high up on large developed islands are victims of light pollution. Chicks that are fledging are attracted to streetlights and are unable to reach the sea. An estimated 20–40% of fledging Barau's Petrels are attracted to the streetlights on Réunion.
The Hydrobatidae's two subfamilies, Oceanitinadae and Hydrobatinae, are probably better treated as distinct families.
Procellariiformes are very closely related to Sphenisciformes (Penguins).
In the Sibley-Ahlquist taxonomy, the tubenoses are included in a greatly enlarged order "Ciconiiformes". This taxonomic treatment is almost certainly erroneous, but the assumption of a close evolutionary relationship may be correct.
At one point (until the beginning of the 20th century), the family Hydrobatidae was named Procellariidae, and the family now called Procellariidae was rendered "Puffinidae." The order itself was called Tubinares. A major early work on this group is F. DuCane Godman's Monograph of the Petrels, five fascicles, 1907—1910., with portraits of figures by John Gerrard Keulemans.