Stomach oil is the light oil composed of neutral dietary lipids found in the proventriculus (fore-gut) of birds in the order Procellariiformes. All albatrosses, procellarids (gadfly petrels and shearwaters) and northern and austral storm petrels use the oil. The only Procellariiformes that do not are the diving petrels.
The chemical make up of stomach oil varies from species to species and between individuals, but almost always contains both wax esters and triglycerides. Other compounds found in stomach oil include glycerol ethers, pristane and squalene. Stomach oil has low viscosity and will solidify into a hard wax if allowed to cool.
It was once thought that stomach oil was a secretion of the proventriculus, but it is now known to be a residue of the diet created by digestion of the prey items such as krill, squid, copepods and fish. It is thought to serve several functions for Procellariiformes, primarily as an energy store; its calorific value is around 40 MJ/kg (9.6 kcal per gram), which is only slightly lower than the value for diesel oil. For this reason a great deal more energy can be stored in oil form as opposed to undigested prey. This can be a real advantage for species that range over huge distances to provide food for hungry chicks, or as a store for lean times when ranging across the sea looking for patchy areas of prey.
Surface nesting petrels and albatross can eject this oil out of their mouths (not nostrils, as has sometimes been suggested) towards attacking predators or conspecific rivals. This oil can be deadly to birds, as it can cause matting of the feathers leading to the loss of flight or water repellency. Against threatening mammals (including humans) it is not outright dangerous, but due to its extremely offensive smell it is usually highly repulsive and liable to spoil a predator's hunting success for quite some time. The smell of the hydrophobic oil cannot be removed with water, and can persist (e.g. on clothing) for months or even years.
Procellariiformes is an order of seabirds that comprises four families: the albatrosses, the petrels and shearwaters, and two families of storm petrels. Formerly called Tubinares and still called tubenoses in English, procellariiforms are often referred to collectively as the petrels, a term that has been applied to all members of the order, or more commonly all the families except the albatrosses. They are almost exclusively pelagic, and have a cosmopolitan distribution across the world's oceans, with the highest diversity being around New Zealand.
Pachyptila is a genus of seabirds in the family Procellariidae and the order Procellariiformes. The members of this genus and the blue petrel form a sub-group called prions. They range throughout the southern hemisphere, often in the much cooler higher latitudes. Three species, the broad-billed prion, the Antarctic prion and the fairy prion, range into the subtropics.
Northern storm petrels are seabirds in the genus Hydrobates in the family Hydrobatidae, part of the order Procellariiformes. The family was once lumped with the similar austral storm petrels in the combined storm petrels, but have been split, as they were not closely related. These smallest of seabirds feed on planktonic crustaceans and small fish picked from the surface, typically while hovering. Their flight is fluttering and sometimes bat-like.
The waved albatross, also known as Galapagos albatross, is one of three species of the family Diomedeidae that occur in the tropics. When they forage, they follow a straight path to a single site off the coast of Peru, about 1,000 km (620 mi) to the east. During the non-breeding season, these birds reside primarily on the Ecuadorian and Peruvian coasts.
The black-footed albatross is a large seabird of the albatross family Diomedeidae from the North Pacific. All but 2.5% of the population is found among the Northwestern Hawaiian Islands. It is one of three species of albatross that range in the northern hemisphere, nesting on isolated tropical islands. Unlike many albatrosses, it is dark plumaged.
The mollymawks are a group of medium-sized albatrosses that form the genus Thalassarche. The name has sometimes been used for the genus Phoebetria as well, but these are usually called sooty albatrosses. They are restricted to the Southern Hemisphere, where they are the most common of the albatrosses. They were long considered to be in the same genus as the great albatrosses, Diomedea, but a study of their mitochondrial DNA showed that they are a monophyletic taxon related to the sooty albatrosses, and they were placed in their own genus.
The northern giant petrel, also known as Hall's giant petrel, is a large, predatory seabird of the southern oceans. Its range overlaps broadly with the range of the related southern giant petrel, albeit slightly further to the north.
The spectacled petrel is a rare seabird that nests only on the high western plateau of Inaccessible Island in the South Atlantic Tristan da Cunha group. It is one of the largest petrels that nests in burrows. This species was formerly considered to be a subspecies of the white-chinned petrel.
The North Pacific albatrosses are large seabirds from the genus Phoebastria in the albatross family. They are the most tropical of the albatrosses, with two species nesting in the Northwestern Hawaiian Islands, one on sub-tropical islands south of Japan, and one nesting on the equator.
Procellaria is a genus of Southern Ocean long-winged seabirds related to prions, and within the order Procellariiformes. The black petrel ranges in the Pacific Ocean, and as far north as Central America. The spectacled petrel is confined to the Atlantic Ocean, and the Westland petrel to the Pacific Ocean. The white-chinned and grey petrel range throughout the higher latitudes of the Southern Ocean.
The northern royal albatross or toroa, is a large seabird in the albatross family. It was split from the closely related southern royal albatross as recently as 1998, though not all scientists support that conclusion and some consider both of them to be subspecies of the royal albatross.
The blue petrel is a small seabird in the shearwater and petrel family, Procellariidae. This small petrel is the only member of the genus Halobaena, but is closely allied to the prions. It is distributed across the Southern Ocean but breeds at a few island sites, all close to the Antarctic Convergence zone.
The Cape petrel, also called the Cape pigeon, pintado petrel, or Cape fulmar, is a common seabird of the Southern Ocean from the family Procellariidae. It is the only member of the genus Daption, and is allied to the fulmarine petrels, and the giant petrels. They are extremely common seabirds with an estimated population of around 2 million.
The Tristan albatross is a large seabird from the albatross family. One of the great albatrosses of the genus Diomedea, it was only widely recognised as a full species in 1998.
Albatrosses, of the biological family Diomedeidae, are large seabirds related to the procellariids, storm petrels, and diving petrels in the order Procellariiformes. They range widely in the Southern Ocean and the North Pacific. They are absent from the North Atlantic, although fossil remains show they once occurred there and occasional vagrants are found. Albatrosses are among the largest of flying birds, and species of the genus Diomedea have the longest wingspans of any extant birds, reaching up to 3.7 m (12 ft). The albatrosses are usually regarded as falling into four genera, but disagreement exists over the number of species.
The fairy prion is a small seabird with the standard prion plumage of blue-grey upperparts with a prominent dark "M" marking and white underneath. The sexes are alike. It is a small prion which frequents the low subantarctic and subtropic seas.
The slender-billed prion or thin-billed prion, is a species of petrel, a seabird in the family Procellariidae. It is found in the southern oceans.
Salvin's prion, also known as the medium-billed prion, is a species of seabird in the petrel family Procellariidae.
The grey petrel, also called the brown petrel, pediunker or grey shearwater is a species of seabird in the Procellariidae, or petrel family. It is pelagic and occurs in the open seas of the Southern Hemisphere, mainly between 32°S and 58°S.
Austral storm petrels, or southern storm petrels, are seabirds in the family Oceanitidae, part of the order Procellariiformes. These smallest of seabirds feed on planktonic crustaceans and small fish picked from the surface, typically while hovering. Their flight is fluttering and sometimes bat-like.