Procellariidae


The family Procellariidae is a group of seabirds that comprises the fulmarine petrels, the gadfly petrels, the diving petrels, the prions, and the shearwaters. This family is part of the bird order Procellariiformes, which also includes the albatrosses and the storm petrels.
The procellariids are the most numerous family of tubenoses, and the most diverse. They range in size from the giant petrels with a wingspan of around, that are almost as large as the albatrosses, to the diving petrels with a wingspan of around that are similar in size to the little auks or dovekies in the family Alcidae. Male and female birds are identical in appearance. The plumage colour is generally dull, with blacks, whites, browns and greys. The birds feed on fish, squid and crustacea, with many also taking fisheries discards and carrion. Whilst agile swimmers and excellent in water, petrels have weak legs and can only shuffle on land, with the giant petrels of the genus Macronectes being the only two species that are capable of proper terrestrial locomotion. 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, a single white egg is laid each breeding season. The parents take it in turns to incubate the egg and to forage for food. The feeding area can be at a great distance from the nest site. The 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. Humans have traditionally exploited several species of fulmar and shearwater for food, fuel, and bait, a practice that continues in a controlled fashion today. Several species are threatened by introduced species attacking adults and chicks in breeding colonies and by long-line fisheries.

Taxonomy and evolution

The family Procellariidae was introduced by the English zoologist William Elford Leach in a guide to the contents of the British Museum published in 1820. The name is derived from the type genus Procellaria which in turn is derived from the Latin word procella meaning "storm" or "gale". The type genus was named in 1758 by the Swedish naturalist Carl Linnaeus in the tenth edition of his Systema Naturae.
Procellariidae is one of families that make up the order Procellariiformes. Before the introduction of molecular phylogenetics, the traditional arrangement was to divide the Procellariiformes into a set of four families: Diomedeidae containing the albatrosses, Hydrobatidae containing all the storm petrels, Pelecanoididae containing the diving petrels and Procellariidae containing the petrels, shearwaters and fulmars. The family Hydrobatidae was further divided into two subfamilies, the northern storm petrels in Hydrobatinae and the southern or austral storm petrels in Oceanitinae. A 1998 analysis of mitochondrial cytochrome b sequences found there was deep genetic divergence between the two subfamilies. Subsequent large-scale multigene studies found that the two subfamilies were not sister taxa. The storm petrels were therefore split into two families: Hydrobatidae containing the northern storm petrels and Oceanitidae, containing the southern storm petrels. The multigene genetic studies found that the diving petrels in the family Pelecanoididae were nested within the family Procellariidae. As a result, the diving petrels was merged into Procellariidae.
The molecular evidence suggests that the albatrosses were the first to diverge from the ancestral stock, and the austral storm petrels next, with the procellariids and northern storm petrels splitting most recently.
Within the procellariid family, a genetic analysis based on the cytochrome b gene published in 2004 indicated that the genus Puffinus contained two distinct clades and was polyphyletic. The genus was therefore split and a group of species moved into the resurrected genus Ardenna. The other genera within the family were found to be monotypic but the relationships between the genera remained unclear. This changed when a multigene genetic study published in 2021 provided a genus-level phylogeny of the family.
There are 99 species of procellariid in 16 genera. The family has usually been broken up into four fairly distinct groups; the fulmarine petrels, the gadfly petrels, the prions, and the shearwaters. With the inclusion of the diving petrels there are now five main groups.
  • The fulmarine petrels include the largest procellariids, the giant petrels, as well as the two fulmar species, the snow petrel, the Antarctic petrel, and the Cape petrel. The fulmarine petrels are a diverse group with differing habits and appearances, but are linked morphologically by their skull features, particularly the long prominent nasal tubes.
  • The four diving petrels are the smallest procellariids with lengths of around and wingspans of. They are compact birds with short wings that are adapted for use under water. They have a characteristic whirring flight and dive into the water without settling. They probably remain all year in the seas near their breeding sites.
  • The gadfly petrels, so named due to their helter-skelter flight, are the 35 species in the genus Pterodroma. The species vary from small to medium sizes, in length, and are long winged with short hooked bills. They are most closely related to Kerguelen petrel which is placed in its own genus Aphrodroma.
  • The prions comprise seven species of true prion in the genus Pachyptila and the closely related blue petrel. Often known in the past as whalebirds, three species have large bills filled with lamellae that they use to filter plankton somewhat as baleen whales do, though the old name derives from their association with whales, not their bills. They are small procellariids, in length, with a prominent dark M-shaped mark across the upperwing of their grey plumage. All are restricted to the southern hemisphere.
  • The shearwaters are adapted for diving after prey instead of foraging on the ocean's surface; several species have been recorded diving deeper than. They are known for the long trans-equatorial migrations undertaken by many species. The shearwaters include the 20 or so species of the genus Puffinus, seven species in the genus Ardenna, as well as the five large Procellaria species and the four Calonectris species. While all these four genera are often known collectively as shearwaters, the Procellaria are called petrels in their common names.

    Morphology and flight

The procellariids are small- to medium-sized seabirds. The largest, the southern giant petrel with a wingspan of, is almost as large as albatrosses; the smallest, the diving petrels have a wingspan of and are similar in size to little auks or dovekies in the family Alcidae. There are no obvious differences between the sexes, although females tend to be slighter. Like all Procellariiformes, the procellariids have a characteristic tubular nasal passage used for olfaction. This ability to smell helps to locate patchily distributed prey at sea and may help locate nesting colonies. The plumage of the procellariids is usually dull, with greys, bluish greys, blacks and browns being the usual colours, although some species have striking patterns such as the Cape petrel.
The technique of flight among procellariids depends on foraging methods. Compared to an average bird, all procellariids have a high aspect ratio and a heavy wing loading. Therefore, they must maintain a high speed in order to remain in the air. Most procellariids use two techniques to do this, namely, dynamic soaring and slope soaring. Dynamic soaring involves gliding across wave fronts, thus taking advantage of the vertical wind gradient and minimising the effort required to stay in the air. Slope soaring is more straightforward: the procellariid turns to the wind, gaining height, from where it can then glide back down to the sea. Most procellariids aid their flight by means of flap-glides, where bursts of flapping are followed by a period of gliding; the amount of flapping dependent on the strength of the wind and the choppiness of the water. Because of the high speeds required for flight, procellariids need to either run or face into a strong wind in order to take off.
The giant petrels share with the albatrosses an adaptation known as a shoulder-lock, a sheet of tendon that locks the wing when fully extended, allowing the wing to be kept up and out without any muscle effort. Gadfly petrels often feed on the wing, snapping prey without landing on the water. The flight of the smaller prions is similar to that of the storm petrels, being highly erratic and involving weaving and even looping the loop. The wings of all species are long and stiff. In some species of shearwater the wings are used to power the birds underwater while diving for prey. Their heavier wing loadings, in comparison with surface-feeding procellariids, allow these shearwaters to achieve considerable depths.
Procellariids generally have weak legs that are set back, and many species move around on land by resting on the breast and pushing themselves forward, often with the help of their wings. The exceptions to this are the two species of giant petrel, which have strong legs used when they feed on land.

Distribution and migration

The procellariids are present in all the world's oceans and most of the seas. They are absent from the Bay of Bengal and Hudson Bay, but are present year round or seasonally in the rest. The seas north of New Zealand are the centre of procellariid biodiversity, with the most species. Among the groups, the fulmarine petrels have a mostly polar distribution, with most species living around Antarctica and one, the northern fulmar ranging in the Northern Atlantic and Pacific Oceans. Of the four species of diving petrel, two are found along the coasts of South America, while the remaining two have circumpolar distributions in the Southern Ocean. The prions are restricted to the Southern Ocean, and the gadfly petrels are found mostly in the tropics with some temperate species. The shearwaters are the most widespread group and breed in most temperate and tropical seas.
Many procellariids undertake long annual migrations in the non-breeding season. Southern species of shearwater such as the sooty shearwater and short-tailed shearwater, breeding on islands off Australia, New Zealand and Chile, undertake transequatorial migrations of millions of birds up to the waters off Alaska and back each year during the austral winter. Manx shearwaters from the North Atlantic also undertake transequatorial migrations from Western Europe and North America to the waters off Brazil and Argentina in the South Atlantic. The mechanisms of navigation are poorly understood, but displacement experiments where individuals were removed from colonies and flown to far-flung release sites have shown that they are able to home in on their colonies with remarkable precision. A Manx shearwater released in Boston returned to its colony in Skomer, Wales within 13 days, a distance of 5,150 kilometres. The gadfly petrels in the genus Pterodroma, breeding in warm temperate locations, also move immense distances to feed; Bermuda petrels nesting on Bermuda regularly travel as far as the seas off Newfoundland, western Ireland and the Bay of Biscay, with individuals covering in a year.