The swallow-tailed gull (''Creagrus furcatus'') is an equatorial
seabird
Seabirds (also known as marine birds) are birds that are 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 enviro ...
in the
gull
Gulls, or colloquially seagulls, are seabirds of the family Laridae in the suborder Lari. They are most closely related to the terns and skimmers and only distantly related to auks, and even more distantly to waders. Until the 21st century, m ...
family
Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...
, Laridae. It is the
only species in the
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
''Creagrus'', which derives from the Latin ''Creagra'' and the Greek ''kreourgos'' which means butcher, also from ''kreas'', meat; according to Jobling it would mean "hook for meat" referring to the hooked
bill
Bill(s) may refer to:
Common meanings
* Banknote, paper cash (especially in the United States)
* Bill (law), a proposed law put before a legislature
* Invoice, commercial document issued by a seller to a buyer
* Bill, a bird or animal's beak
Plac ...
of this species. It was first described by French naturalist and surgeon
Adolphe-Simon Neboux
Adolphe-Simon Neboux (1806–1844) was a French surgeon and naturalist who accompanied the frigate ''Vénus'' under command of Admiral Abel Aubert du Petit-Thouars between the years 1836 and 1839, visiting the Pacific coastline of North America ...
in 1846. Its scientific name is originally derived from the Greek word for gull, "Glaros" and via
Latin
Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...
''Larus'', "gull" and ''furca'' "two-tined fork". It spends most of its life flying and hunting over the open ocean. The main breeding location is in the Galápagos Islands, particularly the rocky shores and cliffs of Hood, Tower and Wolf Islands, with lower numbers on most of the other islands. It is more common on the eastern islands where the water is warmer.
[
It is the only fully ]nocturnal
Nocturnality is an animal behavior characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnal meaning the opposite.
Nocturnal creatures generally have highly developed sens ...
gull and seabird in the world,[ preying on ]squid
True squid are molluscs with an elongated soft body, large eyes, eight arms, and two tentacles in the superorder Decapodiformes, though many other molluscs within the broader Neocoleoidea are also called squid despite not strictly fitting t ...
and small fish which rise to the surface at night to feed on plankton
Plankton are the diverse collection of organisms found in Hydrosphere, water (or atmosphere, air) that are unable to propel themselves against a Ocean current, current (or wind). The individual organisms constituting plankton are called plankt ...
.[
]
Description
The swallow-tailed gull has no structural or plumage
Plumage ( "feather") is a layer of feathers that covers a bird and the pattern, colour, and arrangement of those feathers. The pattern and colours of plumage differ between species and subspecies and may vary with age classes. Within species, ...
differences between the male and female. In the breeding season, the adult has a black plumaged head and a bright red fleshy rim around each eye. Outside the breeding season, the head is white and the eye rim becomes black.[ It has a grayish upper breast, gray mantle, and black wingtips. The mostly black bill has a contrasting white tip.][
]
Night vision
In order to see while hunting for food at night, the swallow-tailed gull's eyes are larger in size and volume than those of any other gull. They also possess a tapetum lucidum
The ''tapetum lucidum'' ( ; ; ) is a layer of tissue in the eye of many vertebrates and some other animals. Lying immediately behind the retina, it is a retroreflector. It reflects visible light back through the retina, increasing the light a ...
in the back of the eye that reflects light back through the retina
The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which then ...
, increasing the amount of light available to the photoreceptor cells
A photoreceptor cell is a specialized type of neuroepithelial cell found in the retina that is capable of visual phototransduction. The great biological importance of photoreceptors is that they convert light (visible electromagnetic radiatio ...
.[
]
Melatonin
A study of melatonin
Melatonin is a natural product found in plants and animals. It is primarily known in animals as a hormone released by the pineal gland in the brain at night, and has long been associated with control of the sleep–wake cycle.
In vertebrates ...
levels of swallow-tailed gulls found them to have no measurable daily melatonin rhythm, whereas a day-feeding gull that was chosen for comparison had the expected higher night time melatonin level for day active birds. High melatonin levels generally make birds sleepy. It is still unknown whether the melatonin levels are a cause or an effect of the swallow-tailed gulls' nocturnal activity.
Distribution and habitat
The swallow-tailed gull is a near-endemic breeding bird of the Galápagos Islands
The Galápagos Islands (Spanish: , , ) are an archipelago of volcanic islands. They are distributed on each side of the equator in the Pacific Ocean, surrounding the centre of the Western Hemisphere, and are part of the Republic of Ecuador ...
, although a few pairs nest on Malpelo Island
Malpelo is a small oceanic island in the eastern Pacific Ocean, located about west of the Colombian mainland with a military post manned by the Colombian Armed Forces. It consists of a sheer and barren rock with three high peaks, the highest ...
off the coast of Colombia
Colombia (, ; ), officially the Republic of Colombia, is a country in South America with insular regions in North America—near Nicaragua's Caribbean coast—as well as in the Pacific Ocean. The Colombian mainland is bordered by the Car ...
. When not breeding, it is totally pelagic
The pelagic zone consists of the water column of the open ocean, and can be further divided into regions by depth (as illustrated on the right). The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or wa ...
, flying and hunting over the open oceans, and migrating eastward to the coasts of Ecuador
Ecuador ( ; ; Quechua: ''Ikwayur''; Shuar: ''Ecuador'' or ''Ekuatur''), officially the Republic of Ecuador ( es, República del Ecuador, which literally translates as "Republic of the Equator"; Quechua: ''Ikwadur Ripuwlika''; Shuar: ''Eku ...
and Peru
, image_flag = Flag of Peru.svg
, image_coat = Escudo nacional del Perú.svg
, other_symbol = Great Seal of the State
, other_symbol_type = Seal (emblem), National seal
, national_motto = "Fi ...
.
Behaviour
Food and feeding
The swallow-tailed gull is unique among the gulls in feeding exclusively nocturnally,[ mostly on ]fish
Fish are aquatic, craniate, gill-bearing 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. Approximately 95% of li ...
and squid
True squid are molluscs with an elongated soft body, large eyes, eight arms, and two tentacles in the superorder Decapodiformes, though many other molluscs within the broader Neocoleoidea are also called squid despite not strictly fitting t ...
which rise to the surface at night to feed on plankton. It leaves the colony as a flock at dusk, with a great deal of screaming and display.[
]
Calls
Calls and displays are quite different from other gulls, most resembling the vocalisations of the black-legged kittiwake
The black-legged kittiwake (''Rissa tridactyla'') is a seabird species in the gull family Laridae.
This species was first described by Carl Linnaeus in his landmark 1758 10th edition of ''Systema Naturae'' as ''Larus tridactylus''. The English ...
and Sabine's gull
Sabine's gull ( ) (''Xema sabini'') also known as the fork-tailed gull or xeme, is a small gull. It is the only species placed in the genus ''Xema''. It breeds in colonies on coasts and tundra, laying two or three spotted olive-brown eggs in a gr ...
. The loudest and most commonly heard call is an alarm referred to as "rattle-and-whistle", a gurgling scream made with the head moving side to side. This call is contagious, with other birds joining in without seeing the cause. A loud and rapid ''kweek, kweek, kweek'' is the greeting call between mates, made with the head and neck curved forward to the ground.
Breeding
The swallow-tailed gull breeds from about 5 years old,[ with pairs frequently staying together from year to year.][ Most breed throughout the year in mixed ]colonies
In modern parlance, a colony is a territory subject to a form of foreign rule. Though dominated by the foreign colonizers, colonies remain separate from the administration of the original country of the colonizers, the '' metropolitan state'' ...
on the cliffs of the Galápagos Islands sometimes on flat areas, and food for the young is hunted from the seas near to the nesting colonies.[ The nest is made on a small platform on a cliff, usually less than 10 m above sea level,][ by covering the rocky ground with small pieces of lava, white coral, and sea urchin spines, which prevent the egg from rolling.][ Nesting birds tend to face the cliff, a habit common among exclusively cliff nesting gulls, such as the black-legged kittiwake.][ The female usually lays one speckled egg per breeding attempt.][ They are asynchronous breeders (can breed any time of the year), and follow a nine-month cycle, or less if an egg or chick is unsuccessful.][ The egg is generally incubated for 31–34 days.][ A chick takes its first flight at about 60–70 days old, and is fed by the adults until about 90 days, when it leaves the land, possibly with the adults, to live over the open seas.][
]
Status
Population trends have not been estimated, but it is not thought to be threatened. The population was estimated to be about 35,000 individuals when it was last considered in 2004.
References
Further reading
*Snow, D.W. & Snow, B.K. (1967). "The breeding cycle of the Swallow-tailed Gull (''Creagrus furcatus'')." ''Ibis'' 109(1):14–24
*Snow, B.K. & Snow, D.W. (1968). "Behavior of the Swallow-tailed Gull of the Galapagos." ''Condor'' 70(3):
External links
*
*
{{Taxonbar, from1=Q1052818, from2=Q10750768
swallow-tailed gull
The swallow-tailed gull (''Creagrus furcatus'') is an equatorial seabird in the gull family, Laridae. It is the only species in the genus ''Creagrus'', which derives from the Latin ''Creagra'' and the Greek ''kreourgos'' which means butcher, al ...
Galápagos Islands coastal fauna
swallow-tailed gull
The swallow-tailed gull (''Creagrus furcatus'') is an equatorial seabird in the gull family, Laridae. It is the only species in the genus ''Creagrus'', which derives from the Latin ''Creagra'' and the Greek ''kreourgos'' which means butcher, al ...
Taxa named by Adolphe-Simon Neboux