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 (or tubenoses), 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 (known as muttonbirds) 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 (as Procellaridæ) 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 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. The storm petrels were therefore split into two families: Hydrobatidae containing the northern storm petrels and Oceanitidae, containing the southern storm petrels. As a result, the diving petrels was merged into Procellariidae. 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.

There are 99 species of procellariid in 16 genera.

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. 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. 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. 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.

Behaviour

Food and feeding

The diet of the procellariids is the most diverse of all the Procellariiformes, as are the methods employed to obtain it. With the exception of the giant petrels, all procellariids are exclusively marine, and the diet of all species is dominated by either fish, squid, crustaceans and carrion, or some combination thereof.

The majority of species are surface feeders, obtaining food that has been pushed to the surface by other predators or currents, or have floated in death. Among the surface feeders some, principally the gadfly petrels, can obtain food by dipping from flight, while most of the rest feed while sitting on the water. These surface feeders are dependent on their prey being close to the surface, and for this reason procellariids are often found in association with other predators or oceanic convergences. Studies have shown strong associations between many different kinds of seabirds, including wedge-tailed shearwaters, and dolphins and tuna, which push shoaling fish up towards the surface.

The fulmarine petrels are generalists, which for the most part take many species of fish and crustacea. The giant petrels, uniquely for Procellariiformes, will feed on land, eating the carrion of other seabirds and seals. They will also attack the chicks of other seabirds. The diet of the giant petrels varies according to sex, with the females taking more krill and the males more carrion.

thumb|The [[broad-billed prion (Pachyptila vittata) filters zooplankton from the water with its wide bill. | alt=Photo of a broad-billed prion on land]]

The three larger prion species have bills filled with lamellae, which act as filters to sift zooplankton from the water. Water is forced through the lamellae and small prey items are collected. This technique is often used in conjunction with a method known as hydroplaning where the bird dips its bill beneath the surface and propels itself forward with wings and feet as if walking on the water. Tropical shearwaters, such as the wedge-tailed shearwater and the Sargasso shearwater, also dive in order to hunt, making the shearwaters the only tropical seabirds capable of exploiting that ecological niche (all other tropical seabirds feed close to the surface). Other exceptions are Barau's petrel (Pterodroma baraui) that breeds at on the island of Réunion in the Indian Ocean, and the snow petrel (Pagodroma nivea) that breeds in Antarctica on mountain ledges up to from the open sea.

Most seabirds are colonial, and the reasons for colonial behaviour are assumed to be similar, if incompletely understood by scientists. Procellariids for the most part have weak legs and are unable to easily take off, making them highly vulnerable to mammalian predators. Most procellariid colonies are located on islands that have historically been free of mammals; for this reason some species cannot help but be colonial as they are limited to a few locations to breed. Even species that breed on continental Antarctica, such as the Antarctic petrel, are forced by habitat preference (snow-free north-facing rock) to breed in just a few locations.

thumb|left|[[Christmas shearwaters (Puffinus nativitatis) are one of the surface-breeding procellariids. Here a pair engages in some mutual preening. | alt=Photo of a pair of Christmas shearwaters on land under vegetation]]

Most procellariids' nests are in burrows or on the surface on open ground, with a smaller number nesting under the cover of vegetation (such as in a forest). All the fulmarine petrels bar the snow petrel nest in the open, the snow petrel instead nesting inside natural crevices. Of the rest of the procellariids the majority nest in burrows or crevices, with a few tropical species nesting in the open. There are several reasons for these differences. The fulmarine petrels are probably precluded from burrowing by their large size (the crevice-nesting snow petrel is the smallest fulmarine petrel) and the high latitudes they breed in, where frozen ground is difficult to burrow into. The smaller size of the other species, and their lack of agility on land, mean that even on islands free from mammal predators they are still vulnerable to skuas,

Breeding season

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 unknown reasons. 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) All procellariid chicks fledge by themselves, and there is no further parental care after fledging. Life expectancy of Procellariidae is between 15 and 20 years; the oldest recorded member was a northern fulmar that was over 50 years.

Threats and conservation

While some species of procellariid have populations that number in the millions, many species are much less common and several are threatened with extinction. Human activities have caused dramatic declines in the numbers of some species, particularly species that were originally restricted to one island. According to the IUCN, 43 species are listed as vulnerable or worse, with 12 critically endangered. Procellariids are threatened by many threats, but introduced species on their breeding grounds, light pollution, marine fisheries particularly bycatch, pollution, exploitation and climate change are the main threats measures as the number of species involved.

The most pressing threat for many species, particularly the smaller ones, comes from species introduced to their colonies. These predators can either directly attack and kill breeding adults, or, more commonly, attack eggs and chicks. Burrowing species that leave their young unattended at a very early stage are particularly vulnerable to attack. Studies on grey-faced petrels breeding on New Zealand's Whale Island (Moutohora) have shown that a population under heavy pressure from Norway rats will produce virtually no young during a breeding season, whereas if the rats are controlled (through the use of poison), breeding success is much higher. Diving species, most especially the shearwaters, are also vulnerable to gillnet fisheries. Studies of gill-net fisheries show that shearwaters (sooty and short-tailed) compose 60% of the seabirds killed by gill-nets in Japanese waters and 40% in Monterey Bay, California in the 1980s, with the total number of shearwaters killed in Japan being between 65,000 and 125,000 per annum over the same study period (1978–1981).

Procellariids are vulnerable to other threats as well. Ingestion of plastic flotsam is a problem for the family as it is for many other seabirds. The Agreement on the Conservation of Albatrosses and Petrels came into force in 2004 and has been ratified by eight countries, Australia, Ecuador, New Zealand, Spain, South Africa, France, Peru and the United Kingdom. The treaty requires these countries to take specific actions to reduce by-catch and pollution and to remove introduced species from nesting islands.

References

Sources

External links

The Agreement for the Conservation of Albatrosses and Petrels (ACAP) Treaty Website
Shearwaters and petrels : Don Roberson's family page