Buller's Shearwater
Encyclopedia
Buller's Shearwater is a Pacific species
of seabird
in the family
Procellariidae
; it is also known as the Grey-backed Shearwater or New Zealand Shearwater. A member of the black-billed wedge-tailed Thyellodroma group, among the larger shearwater
s of the proposed genus
Ardenna, it forms a superspecies
with the Wedge-tailed Shearwater
("P." pacificus).
Adults bird
s are 46–47 cm in length, with a 97–99 cm wingspan, and have been recorded to weigh 342-425 g. The upperside of Buller's Shearwater is bluish grey. A blackish stripe runs from the tertiary remiges to the primary wing coverts. The primary remiges are blackish also; the two black areas do not meet at the hand however; the area between them is a rather light gray, under bright light it may appear almost white. With the bird facing upwards, the pattern gives the impression of a broken black "M", with light gray interspersing areas.
The underside is bright white; on the head the upperside's grey extends town to eye height and the white cheeks may shine up conspicuously, as in the smaller shearwaters of Puffinus
sensu stricto. The rectrices are blackish and the tail is wedge-shaped; bill and iris are dark. Fledged juveniles already have the adult's coloration; the nestlings are covered in grey down feather
s.
Compared to other shearwater
s, the species is unusually easy to identify at sea by its combination of considerable size and the distinctive M-shaped banding pattern on its upperside while flying, uniquely among its genus
and more akin to some gadfly petrel
s (Pterodroma), the prions
(Pachyptila) and their relative, the Blue Petrel
(Halobaena caerulea). These are all much smaller birds, perhaps two-thirds in length and wingspan and less than half in bulk of Buller's Shearwater.
outside the breeding season. Though it occurs in the subarctic
waters off Kamchatka and the Aleutian Islands, it is not documented from the subantarctic
Pacific; this apparent absence might simply be due to the lack of study opportunities in the vast islandless region south of the Polynesian Triangle
however. It is fairly common well off the west coast of the United States
during late summer and early autumn, and can generally be observed not far from land along the whole temperate
and tropical coastlines of the Americas
. Its general absence from most of Melanesia
and western Micronesia
– where human settlement and sea traffic are considerable – is thus probably genuine; only isolated records, such as from the Marianas, Palau
and Yap
, exist from west and southwest of the Marshall Islands
. A vagrant bird was also recorded in the Atlantic once, offshore New Jersey
(USA).
Buller's Shearwater feeds mainly on fish
, squid
, and crustaceans such as the krill
Nyctiphanes australis. It does occasionally follow ship
s such as fishing trawlers, and may be part of a mixed-species feeding flock
. Food is caught mainly at a head's length below the surface at most, the bird either picking it up with the bill only, often out of flight, or briefly inserting the entire head, usually while swimming. It neither dives out of flight very often, nor in a plunge off the water's surface.
It is a colonial nester, breeding predominantly on Tawhiti Rahi and Aorangi, the main islands of the Poor Knights group
offshore northern New Zealand
. This bird nests in burrow
s, rock crevices or under tree
roots, preferring densely forest
ed slopes. Buller's Shearwater can also be found to breed in cracked-up rock on treeless stack
s or cliffs however, and most of the other colonies – on the smaller Poor Knights islands between the main islands and off the southeast of Aorangi – are of such a nature. A pair was observed to breed on the Simmonds Islands in 1980, but this seems to have been an isolated incident.
The breeding season starts in October and lasts for almost half a year. A single egg is incubated for about 51 days, with the parents changing between incubation and feeding every 4 days or so. Time to fledging is not well known, but by analogy with Buller's Shearwater's relatives assumed to be around 100 days.
In the past, it was heavily used as a food source by the Māori, and on Aorangi it suffered massive predation by feral pigs. Its population had crashed to a low of just 100-200 pairs on Aorangi in the late 1930s. The pigs were removed from the island in 1936, and the shearwater population recovered, numbering 200,000 pairs again in the early 1980s to approach carrying capacity
on the island at the end of the 20th century. At all times however, the colonies at Tawhiti Rahi and on the smaller islets could supply birds for the resettlement of Aorangi, and Buller's Shearwater was never considered threatened with extinction in the foreseeable future. Indeed, it is a very abundant bird, with an estimated world population of 2.5 million birds. But as it is not known to occur on any larger island in the region outside the Poor Knights Islands, it is classified as Vulnerable
by the IUCN: a single localized catastrophe could wipe the species out.
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of seabird
Seabird
Seabirds are birds that have adapted to life within the marine environment. While seabirds vary greatly in lifestyle, behaviour and physiology, they often exhibit striking convergent evolution, as the same environmental problems and feeding niches have resulted in similar adaptations...
in the family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Procellariidae
Procellariidae
The family Procellariidae is a group of seabirds that comprises the fulmarine petrels, the gadfly petrels, the prions, and the shearwaters. This family is part of the bird order Procellariiformes , which also includes the albatrosses, the storm-petrels, and the diving petrels.The procellariids are...
; it is also known as the Grey-backed Shearwater or New Zealand Shearwater. A member of the black-billed wedge-tailed Thyellodroma group, among the larger shearwater
Shearwater
Shearwaters are medium-sized long-winged seabirds. There are more than 30 species of shearwaters, a few larger ones in the genus Calonectris and many smaller species in the genus Puffinus...
s of the proposed genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
Ardenna, it forms a superspecies
Superspecies
A superspecies is a group of at least two more or less distinctive species with approximately parapatric distributions. Not all species complexes, whether cryptices or ring species are superspecies, and vice versa, but many are...
with the Wedge-tailed Shearwater
Wedge-tailed Shearwater
The Wedge-tailed Shearwater, Puffinus pacificus is a medium-large shearwater in the seabird family Procellariidae. It is one of the shearwater species that is sometimes referred to as a Muttonbird, like the Sooty Shearwater of New Zealand and the Short-tailed Shearwater of Australia...
("P." pacificus).
Description
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
s are 46–47 cm in length, with a 97–99 cm wingspan, and have been recorded to weigh 342-425 g. The upperside of Buller's Shearwater is bluish grey. A blackish stripe runs from the tertiary remiges to the primary wing coverts. The primary remiges are blackish also; the two black areas do not meet at the hand however; the area between them is a rather light gray, under bright light it may appear almost white. With the bird facing upwards, the pattern gives the impression of a broken black "M", with light gray interspersing areas.
The underside is bright white; on the head the upperside's grey extends town to eye height and the white cheeks may shine up conspicuously, as in the smaller shearwaters of Puffinus
Puffinus
Puffinus is a genus of seabirds in the order Procellariiformes. It comprises about 20 small to medium-sized shearwaters. There are two other shearwater genera: Calonectris, which comprises three large shearwaters, and Procellaria with another four large species...
sensu stricto. The rectrices are blackish and the tail is wedge-shaped; bill and iris are dark. Fledged juveniles already have the adult's coloration; the nestlings are covered in grey down feather
Down feather
The down of birds is a layer of fine feathers found under the tougher exterior feathers. Very young birds are clad only in down. Powder down is a specialized type of down found only in a few groups of birds. Down is a fine thermal insulator and padding, used in goods such as jackets, bedding,...
s.
Compared to other shearwater
Shearwater
Shearwaters are medium-sized long-winged seabirds. There are more than 30 species of shearwaters, a few larger ones in the genus Calonectris and many smaller species in the genus Puffinus...
s, the species is unusually easy to identify at sea by its combination of considerable size and the distinctive M-shaped banding pattern on its upperside while flying, uniquely among its genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
and more akin to some gadfly petrel
Gadfly petrel
The gadfly petrels are seabirds in the bird order Procellariiformes. These medium to large petrels feed on food items picked from the ocean surface....
s (Pterodroma), the prions
Prion (bird)
The Prions are small petrels in the genera Pachyptila and Halobaena. They form one of the four groups within the Procellariidae , along with the gadfly petrels, shearwaters and fulmarine petrels....
(Pachyptila) and their relative, the Blue Petrel
Blue Petrel
The Blue Petrel is a small seabird in the family Procellariidae. This small petrel is the only member of the genus Halobaena but is closely allied to the prions.-Taxonomy:...
(Halobaena caerulea). These are all much smaller birds, perhaps two-thirds in length and wingspan and less than half in bulk of Buller's Shearwater.
Range and ecology
This species is pelagic like the other Ardenna shearwaters; it is a transequatorial migrant ranging across most of the Pacific OceanPacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
outside the breeding season. Though it occurs in the subarctic
Subarctic
The Subarctic is a region in the Northern Hemisphere immediately south of the true Arctic and covering much of Alaska, Canada, the north of Scandinavia, Siberia, and northern Mongolia...
waters off Kamchatka and the Aleutian Islands, it is not documented from the subantarctic
Subantarctic
The Subantarctic is a region in the southern hemisphere, located immediately north of the Antarctic region. This translates roughly to a latitude of between 46° – 60° south of the Equator. The subantarctic region includes many islands in the southern parts of the Indian Ocean, Atlantic Ocean and...
Pacific; this apparent absence might simply be due to the lack of study opportunities in the vast islandless region south of the Polynesian Triangle
Polynesian Triangle
The Polynesian Triangle is a region of the Pacific Ocean with three island groups at its corners: Hawaii, Easter Island and New Zealand. It is often used as a simple way to define Polynesia....
however. It is fairly common well off the west coast of the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
during late summer and early autumn, and can generally be observed not far from land along the whole temperate
Temperate
In geography, temperate or tepid latitudes of the globe lie between the tropics and the polar circles. The changes in these regions between summer and winter are generally relatively moderate, rather than extreme hot or cold...
and tropical coastlines of the Americas
Americas
The Americas, or America , are lands in the Western hemisphere, also known as the New World. In English, the plural form the Americas is often used to refer to the landmasses of North America and South America with their associated islands and regions, while the singular form America is primarily...
. Its general absence from most of Melanesia
Melanesia
Melanesia is a subregion of Oceania extending from the western end of the Pacific Ocean to the Arafura Sea, and eastward to Fiji. The region comprises most of the islands immediately north and northeast of Australia...
and western Micronesia
Micronesia
Micronesia is a subregion of Oceania, comprising thousands of small islands in the western Pacific Ocean. It is distinct from Melanesia to the south, and Polynesia to the east. The Philippines lie to the west, and Indonesia to the southwest....
– where human settlement and sea traffic are considerable – is thus probably genuine; only isolated records, such as from the Marianas, Palau
Palau
Palau , officially the Republic of Palau , is an island nation in the Pacific Ocean, east of the Philippines and south of Tokyo. In 1978, after three decades as being part of the United Nations trusteeship, Palau chose independence instead of becoming part of the Federated States of Micronesia, a...
and Yap
Yap
Yap, also known as Wa'ab by locals, is an island in the Caroline Islands of the western Pacific Ocean. It is a state of the Federated States of Micronesia. Yap's indigenous cultures and traditions are still strong compared to other neighboring islands. The island of Yap actually consists of four...
, exist from west and southwest of the Marshall Islands
Marshall Islands
The Republic of the Marshall Islands , , is a Micronesian nation of atolls and islands in the middle of the Pacific Ocean, just west of the International Date Line and just north of the Equator. As of July 2011 the population was 67,182...
. A vagrant bird was also recorded in the Atlantic once, offshore New Jersey
New Jersey
New Jersey is a state in the Northeastern and Middle Atlantic regions of the United States. , its population was 8,791,894. It is bordered on the north and east by the state of New York, on the southeast and south by the Atlantic Ocean, on the west by Pennsylvania and on the southwest by Delaware...
(USA).
Buller's Shearwater feeds mainly on fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
, squid
Squid
Squid are cephalopods of the order Teuthida, which comprises around 300 species. Like all other cephalopods, squid have a distinct head, bilateral symmetry, a mantle, and arms. Squid, like cuttlefish, have eight arms arranged in pairs and two, usually longer, tentacles...
, and crustaceans such as the krill
Krill
Krill is the common name given to the order Euphausiacea of shrimp-like marine crustaceans. Also known as euphausiids, these small invertebrates are found in all oceans of the world...
Nyctiphanes australis. It does occasionally follow ship
Ship
Since the end of the age of sail a ship has been any large buoyant marine vessel. Ships are generally distinguished from boats based on size and cargo or passenger capacity. Ships are used on lakes, seas, and rivers for a variety of activities, such as the transport of people or goods, fishing,...
s such as fishing trawlers, and may be part of a mixed-species feeding flock
Mixed-species feeding flock
A mixed-species feeding flock, also termed a mixed-species foraging flock, mixed hunting party or informally bird wave, is a flock of usually insectivorous birds of different species, that join each other and move together while foraging...
. Food is caught mainly at a head's length below the surface at most, the bird either picking it up with the bill only, often out of flight, or briefly inserting the entire head, usually while swimming. It neither dives out of flight very often, nor in a plunge off the water's surface.
It is a colonial nester, breeding predominantly on Tawhiti Rahi and Aorangi, the main islands of the Poor Knights group
Poor Knights Islands
The Poor Knights Islands are a group of islands off the east coast of the Northland Region of the North Island of New Zealand. They are located to the northeast of Whangarei, and lie offshore half way between Bream Head and Cape Brett. Uninhabited since the 1820s, they are a nature reserve and...
offshore northern New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
. This bird nests in burrow
Burrow
A burrow is a hole or tunnel dug into the ground by an animal to create a space suitable for habitation, temporary refuge, or as a byproduct of locomotion. Burrows provide a form of shelter against predation and exposure to the elements, so the burrowing way of life is quite popular among the...
s, rock crevices or under tree
Tree
A tree is a perennial woody plant. It is most often defined as a woody plant that has many secondary branches supported clear of the ground on a single main stem or trunk with clear apical dominance. A minimum height specification at maturity is cited by some authors, varying from 3 m to...
roots, preferring densely forest
Forest
A forest, also referred to as a wood or the woods, is an area with a high density of trees. As with cities, depending where you are in the world, what is considered a forest may vary significantly in size and have various classification according to how and what of the forest is composed...
ed slopes. Buller's Shearwater can also be found to breed in cracked-up rock on treeless stack
Stack (geology)
A stack is a geological landform consisting of a steep and often vertical column or columns of rock in the sea near a coast, isolated by erosion. Stacks are formed through processes of coastal geomorphology, which are entirely natural. Time, wind and water are the only factors involved in the...
s or cliffs however, and most of the other colonies – on the smaller Poor Knights islands between the main islands and off the southeast of Aorangi – are of such a nature. A pair was observed to breed on the Simmonds Islands in 1980, but this seems to have been an isolated incident.
The breeding season starts in October and lasts for almost half a year. A single egg is incubated for about 51 days, with the parents changing between incubation and feeding every 4 days or so. Time to fledging is not well known, but by analogy with Buller's Shearwater's relatives assumed to be around 100 days.
In the past, it was heavily used as a food source by the Māori, and on Aorangi it suffered massive predation by feral pigs. Its population had crashed to a low of just 100-200 pairs on Aorangi in the late 1930s. The pigs were removed from the island in 1936, and the shearwater population recovered, numbering 200,000 pairs again in the early 1980s to approach carrying capacity
Carrying capacity
The carrying capacity of a biological species in an environment is the maximum population size of the species that the environment can sustain indefinitely, given the food, habitat, water and other necessities available in the environment...
on the island at the end of the 20th century. At all times however, the colonies at Tawhiti Rahi and on the smaller islets could supply birds for the resettlement of Aorangi, and Buller's Shearwater was never considered threatened with extinction in the foreseeable future. Indeed, it is a very abundant bird, with an estimated world population of 2.5 million birds. But as it is not known to occur on any larger island in the region outside the Poor Knights Islands, it is classified as Vulnerable
Vulnerable species
On 30 January 2010, the IUCN Red List of Threatened Species identified 9694 Vulnerable species, subspecies and varieties, stocks and sub-populations.-References:...
by the IUCN: a single localized catastrophe could wipe the species out.
Further reading
- Harrison, Peter (1983): Seabirds: An Identification Guide. Croon Helm, Beckenham. ISBN 0-7099-1207-2
- National Geographic SocietyNational Geographic SocietyThe National Geographic Society , headquartered in Washington, D.C. in the United States, is one of the largest non-profit scientific and educational institutions in the world. Its interests include geography, archaeology and natural science, the promotion of environmental and historical...
(2002): Field Guide to the Birds of North America. National Geographic, Washington DC. ISBN 0-792-26877-6