SHEARWATERS AND PETRELS
Short-tailed shearwater Shearwaters and petrels belong to a group called Procellariidae, known in the past as tubenoses. They are the most widely distributed of all bird species, ranging from 250 kilometers inland in the Antarctic to the nearest pieces of land to the North Pole. They also migrate great distances. Shearwaters tagged by the Census of Marine Life’s Tagging of Pacific Predators (TOPP) project off New Zealand made a 262-day, 39,790-mile round-trip journey in a figure-eight pattern, the longest animal migration ever recorded electronically at the time.
Shearwaters and petrels are a large family of birds. They are divided into four groups: 1) fulmars (cold water birds found mostly in the southern hemisphere); 2) prions (southern hemisphere birds, smaller in size than fulmars; 3) gadfly petrels (a group with 30 or species that nest underground in large colonies); 4) true shearwaters (a group with 23 species that have long, thin bills adapted for catching fish and zooplankton underwater).
Many shearwaters and petrels live on remote islands or remote locations where predators are not present. Most lay their eggs in burrows. Many establish huge colonies. True shearwaters mostly visit their burrows at night. Shearwaters and petrels lay their eggs and brood their young in holes. During the day their breeding areas are quiet places as they adults are either at sea feeding or in their holes with their eggs or chicks, which offer some protection from the skuas and gulls that harass them. Shearwater and petrel adults extract oil from the sea creatures they eat and regurgitate in the mouths of their young. They also squirt oil at intruders. The oil often gets all over the place. This combined with the smell of the birds themselves makes their colonies very smelly places.
Websites and Resources: Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Encyclopedia of Life eol.org; Smithsonian Oceans Portal ocean.si.edu/ocean-life-ecosystems ; MarineBio marinebio.org/oceans/creatures; Expert: Paul Scofield, of New Zealand’s Canterbury Museum and co-author of “Albatrosses, Petrels and Shearwaters of the World”.
Shearwater and Petrel Species
Gadfly petrels have short, stout bill with a hook for gripping and a sharp edge for cutting up small squid and fish. Puffins and mutton birds are true shearwaters, which are highly social birds, that sometimes from dense feeding rafts in the middle of the sea.
Storm petrels and diving petrels are separate families birds. They too nest in burrows and form colonies. Some species of storm petrel have long legs they use to bounce or “walk” on the water while feeding. Some species migrate long distances Diving petrels have short, stubby wings that are ideal for flying in the air and in the water. They are known for their ability to dive deep in the water, staying submerged for considerable periods of time, as they pursue fish.
Sooty shearwaters have been recorded flying 40,000 miles around the Pacific Ocean in a year, the longest electronically-recorded animal migration. Scientist have tracked 19 of the birds from breeding colonies New Zealand. These shearwaters fly east from New Zealand then north to wintering areas, some flew to waters off Japan, others to the Alaska and California, places where food such as krill is abundant..
Shearwater and Petrel Behavior and Senses
Audobon's Shearwater Shearwaters and petrels spend much of their time flying over the open sea feeding on whatever they can get their beaks on. Shearwaters get their name from the habit of many species of skimming along the surface of the sea when hunting.
Shearwaters and petrel nostrils are protected by a pair of tubes which extend down the beak and allow them to smell better than other birds. It is not quite clear what they use their sense of smell for. They hunt at sea where smell is not much of an advantage. Maybe smell helps them locate their hole in their crowded colonies.
Shearwaters have extraordinary navigation abilities. In a famous case, a shearwater was taken from the island of Stockholm in west Wales by plane to Boston, 5,100 kilometers way and released. It found its way back to its burrow 12½ days later. It is not known how it found its way back.
Petrels and some other sea birds have nostrils that excrete excess salt. Once thought to be airspeed indicators, the nostrils are a long, horny tubes perched above the beak. Salt fluids from glands above the eyes pass through the nostril and drip off the bill.
Greater shearwaters (Scientific name:Puffinus gravis) are marine birds distributed throughout the Atlantic ocean region. They as far as the Tristan da Cunha group, the Falkland Islands and Gough Island and migrate to the North Atlantic during the winter to northeast Canada and sometimes as far north as Greenland. Migration to the breeding grounds involves a flight east past Britain and Iberia, than turning south to reach their Southern Hemisphere breeding grounds. Greater shearwaters spend a lot time over the cool open ocean and breed on sloping ground, mainly in grassland or woodland areas. Their average lifespan in the wild is seven years. [Source: Maryanne Spady, Animal Diversity Web (ADW) /=]
Greater shearwaters are a large shearwater species. They range in weight from 715 to 950 grams (25.2 to 33.5ounces) and are 43 to 51 centimeters (1.4 to 1.7 feet) length, with a wingspan of 100 to 118 centimeters. (3.3 to 3.9 feet). According to Animal Diversity Web: Colouring is unique with a combination of pale underparts with a poorly defined dark patch on the belly. White bands of plumage occur across the uppertail-coverts and also across the hindneck, emphasizing the Greater Shearwaters strongly capped appearance. Upperparts are dark gray-brown to black with light feather edgings to give a scaled appearance. Flight feathers have black upper- and undersurfaces. The tubenosed bill is long, thin, and black. The legs are pink to grey with webbed feet, and eyes are brown. Chicks have bluish-grey down and juveniles are similar to adults but greyer with paler fringes to feathers to give less scaled appearance. There is no Sexual Dimorphism (differences between males and females): in terms of size or colour between males and females. /=\
In the past, greater shearwaters provided food and bait for seamen, but this practice was given up long ago. Aside from occasional contacts with fishermen, and Tristan islanders, greater shearwaters have almost no contact with humans. They are not endangered. They are designated as a species of least concern on the International Union for Conservation of Nature (IUCN) Red List and have no special status according to the Convention on International Trade in Endangered Species (CITES).
The great numbers of greater Shearwaters with a minimum of five million breeding pairs on Tristan da Cunha, 600,000 to three million pairs on Gough Island, and small numbers on Falkland Islands. Their breeding range is restricted to only four known sites.Their greatest threat comes from Tristan islanders. Each year, a few thousand adults, and 50,000 chicks are taken. There are demands to establish a quota system there. Sometimes greater shearwaters are snared by commercial fishermen's baited hooks. /=\
Great Shearwater Behavior, Flying and Swimming
Greater shearwaters are graceful flyers and skilled underwater divers but are clumsy and awkward on land. They spend the majority of their lives in the air. Often times the only time they flap their wings is when need a little lift; otherwise the soar using air currents. The name 'shearwater' comes from their ability to fly just above the surface of the ocean, closely following the contour of the waves with their wings outstretched — shearing the water surface with the pointed tips of the wings. These birds are also agile underwater, capable of doing 180 degree turns guided by their wings. They sense using vision, touch, sound and chemicals usually detected with smell. [Source: Maryanne Spady, Animal Diversity Web (ADW) /=]
Greater shearwaters are social birds. They fly, hunt and migrate together in flocks, and can often be seen as flocks following ships for food. They take part in transequatorial migrantions, breeding in the Southern Hemisphere and wintering in the Northern Hemisphere. /=\
According to Animal Diversity Web: Individuals exhibit a harsh raucous call when feeding, much like a gull, and they also exhibit a vocal croak upon returning to a nest at night. Calls are sexually dimorphic, the females with shorter calls, and with a lower frequency inspiratory phrase than the frequency of the first harmonic of the longer expiratory phrase. This is reversed in males. Individuals can discriminate between female and male calls which is potentially useful in mate selection. Greater Shearwaters are sufficiently large to be relatively secure from predation by Great Skuas (Catharacta antarctica), a major predator in this area. As a result of this, Greater Shearwaters have no nocturnal (active at night), habits as they can display during the day. /=\
Great Shearwaters Feeding and Reproduction
According to Animal Diversity Web: Greater Shearwaters feed in groups where aggressive intraspecific feeding competition is evident through lashing with bills and wings. They eat mostly fish and squid, with occasional feeding on crustaceans, fish entrails, and other refuse discarded by fishing vessels. They hunt by plunge-diving from heights of 6-10 meters or taking prey from surface seizing or pursuit diving. /=\
Surface-seizing consists of the 'walking on water' that is usually associated with Storm Petrels. Without entirely folding its wings, a Greater Shearwater lands on the water surface with its feet, balances with its wings, and "walks" forward over the water as it picks up food from near the surface. /=\
Plunge-diving involves striking the water surface from heights of 6-10 meters with belly and feet and then instantly lowering the head under the water surface to lead into a smooth submersion. Occasionally, a Greater Shearwater might briefly halt 0.5 meters above the water surface, spread its feet, then plunge headfirst underneath the water. After the dive, the bird bursts out of the water and almost directly into flight. /=\
The breeding season commences in October and often lasts until December. Breeding takes place in the Southern Hemisphere and is restricted to the far south oceanic islands: Tristan da Cunha group, Falkland Island, and Gough Island. Greater shearwaters are colonial nesters, nesting in burrows or crevices among boulders along hilly island shores. The female produces a single, white, oval, and slightly pointed egg. The egg is incubated for 53-57 days, and an altricial offspring is then hatched. Both male and female care for young. Offspring become independent of their parents at about 105 days./=\
Diving petrels (Scientific name: Pelecanoididae) look more like auks than other shearwaters and petrels and known for diving through the crests of waves while in flight! Comprising only one genus and four or five species, these unusual birds are found in the southern hemisphere, in high latitudes. One species is circumpolar in distribution, and several nest on islands south of the Antarctic Convergence. The taxonomy of this family is still debated; some scientists place them within Procellariidae. [Source: Danielle Cholewiak, Animal Diversity Web]
Diving petrels are rather scarce in the fossil record, the first evidence of this family comes from the early Pliocene Period (5.4 million to 2.4 million years ago) in South Africa. /=\ Although there is much debate over the taxonomy within Procellariiformes, diving petrels are usually considered to be most closely related to the typical petrels, family Procellariidae. /=\
Humans generally have had little contact with diving petrels and have not disturbed them very much. However at least one species is considered threatened, and was nearly wiped out during the years of heavy guano exploitation. By removing guano from small islands, humans destroyed much of the habitat that these birds relies on. They have also been killed and harmed by predation from introduced animal. Domestic cats have killed many birds. /=\
Diving Petrel Characteristics and Reproduction
According to Animal Diversity Web: Morphologically, diving petrels resemble northern auks (alcids) much more than they resemble other procellariiform birds, and their similarities have often been noted as a remarkable example of convergent evolution. They have short wings and small, short necks, and a notably compact body. Their bill is short, broad, and hooked, with a complex rhamphotheca, as in other petrels.
They have the characteristic procellariiform external tubular nostrils, which may, at times, be the easiest way to distinguish them from the smaller alcids. In the diving petrel, these nostrils are reduced and open upwards, which is likely an adaptation for diving. These species tend to be rather similar in appearance; distinctions in bill form, shape of the lower jaw arch and small processes in the nostrils can be used to distinguish them. Their front toes are webbed, and their legs are set far back on their bodies, rendering them clumsy on land like many other procellariiform birds. Their plumage is dark grey or brown above and white below. /=\
They approach land mainly for breeding, though individuals may start visiting breeding grounds long beforehand. They are gregarious and strictly nocturnal (active at night), on land. Each pair burrows into the soil, excavating their nest holes using their claws and bill; they will even nest on snow covered islands after the land thaws. As in all Procellariiformes, females lay a single egg, and both sexes take turns incubating. The male and female switch shifts nightly, so that the diving petrels have the shortest incubation stints within Procellariiformes (in stark contrast to the great albatrosses, who may incubate an egg for several weeks before being relieved by a partner). Many individuals do seem to visit the breeding colony outside of the breeding season; in general, they are considered to be dispersive, rather than migratory (make seasonal movements between regions, such as between breeding and wintering grounds),, but in truth their movements are not well known. /=\
Diving Petrel Flying, Diving and Swimming Abilities
Diving Petrels birds are highly adapted to aquatic life. They dive to catch most of their prey (crustaceans, small fish, and cephalopods), and have a gular pouch in which they can carry food. When diving they use their feet and tail as rudders; experiments have shown that the Common diving petrel can dive up to 64 meters, with approximately 30 meters being the average depth. They will dive to evade danger as well. /=\
Their general mode of flight (referred to as 'whirring' flight) is more similar to alcids than to other petrels. Diving petrels are excellent swimmers and fast in flight; they have the unique ability to 'fly' through waves, plunging through the crest of one wave and coming out on the other side still flying. Unlike other petrels, the flight feathers of diving petrels are moulted simultaneously, leaving the birds flightless while they grow back. They are still quite adept at feeding, however; without feathers, their wings resemble penguin flippers. Their natural body weight is near the limit that their wings can support, so an increase in body weight can also leave them flightless for a time!
Common Diving Petrels
Common diving petrels (Scientific name: Pelecanoides urinatrix) are found in the Southern Ocean between 35̊ and 55̊ degrees South, in an area between the subtropical convergence and subantarctic waters. They are found mostly around the islands they use for breeding. There are six recognized subspecies, each corresponding, to a population around a set of breeding islands. They are: 1) P. u. coppingeri on offshore islands off southern Chile, 2) P. u. berard, which breeds on the Falkland Islands, 3) P. u. dacunhae, found on the Tristan da Cunha island group and Gough Island, 4) P. u. chathamensis, found on the Solander, Stewart, Snares, and Chatham islands, 5) P. u. excsul, found in the southern Indian ocean near South Georgia, Auckland, the Antipodes, and Campbell Islands, and 6) P. u. urinatrix, on islands off the southern coast of Australia, Tasmania, and New Zealand. [Source: Tanya Dewey, Animal Diversity Web (ADW) /=]
Common diving petrels live in temperate, polar, saltwater and marine environments and are typically found in coastal areas. They spend 10 months of the year on or near oceanic islands on which they breed. Not much is known about what they do and where they are during the two months of the year that they are not at the breeding colonies. Islands are usually predator free, but non-native predators have been introduced in some areas.
Diving petrels are similar physically and ecologically to the northern hemisphere puffins, murres, and auklets (Alcidae), especially little auks (Alle alle). The species name urinatrix comes from the Latin "urinator," which means diver. Their lifespan in the wild is typically 6.5 (high) years. Average annual survival of adults is estimated at 75 percent. Young have a high survival rate to fledging, of about 87 percent, but post-fleding mortality can be high.
Common diving petrels have a wide range and large population sizes, They are not endangered. They are designated as a species of least concern on the International Union for Conservation of Nature (IUCN) Red List and have no special status according to the Convention on International Trade in Endangered Species (CITES). Their residence time on breeding colonies makes them particularly vulnerable to non-native predators, such as weasels. As of 2004, worldwide populations were estimated to number 14 million birds. /=\
Common Diving Petrel Characteristics and Behavior
Common diving petrels range in weight from 86 to 185 grams (3 to 6.5 ounces) and range in length from 20 to 25 centimeters (7.9 to 10 inches). Sexual dimorphism (differences between males and females) is minimal: Both sexes are roughly equal in size and look similar. [Source: Tanya Dewey, Animal Diversity Web (ADW) /=]
According to Animal Diversity Web: Like other diving petrels,common diving petrels are smaller, stoutly built seabirds with robust bills, black plumage dorsally, and white plumage on the chin, breast, and belly. The scapulars have white tips, forming a faint stripe on the wing. The face and sides of the neck are more brown than black and the black plumage fades gradually to the whiter plumage of the ventral surfaces. The bill is black and the legs and feet are blue. They are indistinguishable from South Georgia diving petrels (Pelecanoides georgicus), except in the hand, where they may be distinguished by the brown inner webs of their outer primary feathers (light colored in South Georgia diving petrels). They are also distinguished by the dimensions and configuration of their bills and nostrils from other Pelecanoides species. The six recognized subspecies differ slightly in body measurements and bill size, but no comprehensive study has been conducted. Sexual Dimorphism (differences between males and females): is not reported. Like other diving petrels, they are able to store and transport prey items in a gular pouch, formed by a distensible portion of skin in the throat. This characteristic is hinted at by their generic name Pelecanoides, referring to its similarity to the gular sac of pelicans (Pelecanidae).
Common diving petrels are diurnal (active during the daytime), nocturnal (active at night), motile (move around as opposed to being stationary), sedentary (remain in the same area), social colonial (living together in groups or in close proximity to each other). Home range sizes have not been reported. They are thought to be fairly sedentary, remaining more or less in the area of their breeding colony year-round, although they may venture into the open ocean to forage outside of the breeding season and some studies suggest seasonal movements. Like other diving petrels, these birds fly with characteristic fast wing beats close to the water. They seem to molt all of their flight feathers at once, leaving them flightless for several weeks. However, the loss of their primary feathers doesn't impact their ability to dive and capture prey.
Common diving petrels sense using vision, touch, sound and chemicals usually detected with smell and communicate with sound. They are noisy birds, often calling while flying, approaching or leaving colonies, and while on the ground or on their nests. Males and females use different calls. Males sound a bit like a rising "kooo-ah," whereas females give a longer "kuaka-did-a-did" call. Common diving petrels are found most of the year on islands where they form dense breeding colonies. They forage in the offshore and continental shelf regions around their breeding islands. They spend the night in burrows during the breeding season and seem to forage mainly during the day, although they also forage at night on vertically migrating plankton. Outside of the breeding season they are seen alone or in small rafts and generally don't associate with other bird species while foraging.
Common Diving Petrel Feeding and Predators
Common diving petrels feed primarily on aquatic crustaceans, mainly copepods, amphipods (especially Hyperiella antarctica and Hyperoche medusarum), euphasiid krill, and some isopods. They use their wings to propel them underwater and catch most of their prey in underwater pursuit. They use their legs to steer. They can dive to depths of 60 meters. (197 feet) [Source: Tanya Dewey, Animal Diversity Web (ADW) /=]
Common diving petrels mainly feed in near shore areas around their breeding colonies but have also been observed in pelagic (open ocean) waters outside of the breeding season. South Georgia diving petrels specialize on euphasiid krill, whereas common diving petrels dive deeper for prey, primarily going after copepods and amphipods in the breeding season, although they commonly take euphasiid krill outside of the breeding season.
Common diving petrels have few natural predators other than gulls and skuas but they are preyed on by non-native predators in their breeding colonies, such as domestic cats, ship rats, stoats, and least weasels. Like other diving petrels, they seem to dive in response to threats rather than fly. They escape predation by gulls and skuas by visiting their nesting colonies mainly at night, landing briefly outside of their burrows and making a quick retreat to the safety of the burrow upon arrival. If they are forced to walk any distance on land to their burrow, there is a high probability that they will fall prey to larger birds.
Common Diving Petrel Reproduction, Nesting and Young
Common diving petrels engage in seasonal breeding. They breed once a year. Breeding season varies across their range, from April to December, earlier in the north and later in the south. The number of eggs laid each season is one. The time to hatching ranges from 53 to 55 days, with the fledging age ranging from 45 to 59 days. Females and males reach sexual maturity at two to three years.
Common diving petrels nest for much of the year in large breeding colonies. Nests are placed in burrows, rock crevices, or under the protection of thick vegetation. Nesting colonies are found in vegetated slopes of islands, occasionally on flat ground.Burrows are dug in soft substrates, usually with vegetation or rocks obscuring the burrow entrance. Burrows are from 25 to 150 centimeters long. Some colonies have a density of one nest per square meter. These birds congregate at breeding colonies about five months before breeding commences. Colonies are busy with birds in the pre-laying period. Females go to sea to feed before returning to the colony to lay a single, white egg. Egg laying may occur in July in the northernmost part of their range and as late as December in the southernmost portions of their range. Egg laying can be extended, with egg laying occurring for seven weeks in the Crozet Islands.
Common diving petrels are monogamous (have one mate at a time). Males and females begin to visit nesting colonies well before egg-laying. Individuals occupy small nesting territories and dig a burrow up to 1.5 meters long in soft soil, sand, or scree. Individuals call to indicate that their territory is inhabited and perhaps to advertise for a mate. Males and females help to raise their single offspring together. During the pre-fertilization stage provisioning and protecting is done by females. During the pre-birth stage provisioning is done by females and protecting is done by males and females. During the pre-weaning stage provisioning and protecting are done by females and males.
Common diving petrel parents both incubate, brood, and feed their young. Young are altricial. This means that young are born relatively underdeveloped and are unable to feed or care for themselves or move independently for a period of time after birth. Young hatch with a covering of gray down. After the brooding period, parents visit their young an average of 1.88 times per day to deliver regurgitated meals of around 26 grams.
Young are brooded for 10 to 15 days, and are then visited for feedings until they are about 35 days old, at 115 to 125 percent of adult body weights. Fledging occurs at 45 to 59 days. Young common diving petrels begin to visit breeding colonies in the year after their hatching and will reproduce for the first time in their 2nd or 3rd year. /=\
Image Sources: Wikimedia Commons, NOAA
Text Sources: Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Wikipedia, National Geographic, Live Science, BBC, Smithsonian, New York Times, Washington Post, Los Angeles Times, The New Yorker, Reuters, Associated Press, Lonely Planet Guides and various books and other publications.
Last Updated May 2023