Black-throated loon
Black-throated loon | |
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Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Aves |
Order: | Gaviiformes |
Family: | Gaviidae |
Genus: | Gavia |
Species: | G. arctica
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Binomial name | |
Gavia arctica | |
Subspecies | |
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Range of the black-throated loon Breeding Non-breeding
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Synonyms | |
Colymbus arcticus Linnaeus, 1758 |
The black-throated loon (Gavia arctica), also known as the Arctic loon and the black-throated diver, is a
The black-throated loon measures about 70 cm (28 in) in length and can weigh anywhere from 1.3 to 3.4 kilograms (2.9 to 7.5 lb). In breeding plumage, the adult of the nominate subspecies has mostly black upperparts, with the exception of some of the mantle and scapulars, which have white squares. The head and hindneck are grey, and the sides white and striped black. Most of the throat is also black, giving this bird the name "black-throated loon". The colour of the throat patch can be used to distinguish the two subspecies; the throat patch of the other subspecies, G. a. viridigularis, is green. The underparts are mostly white, including the bottom of the throat. The flanks are also white, a feature which can be used to separate this bird from the Pacific loon. When it is not breeding, the black patch on the throat is absent, replaced with white; most of the black lines on the throat are also missing, except those on the bottom sides, and the upperparts are unpatterned with the exception of a few white spots on the upperwing. The juvenile is similar to the non-breeding adult, except more brown overall.
The timing of the breeding season is variable; in the southern part of its range, this loon starts breeding in April, whereas in the northern portion, it waits until after the spring thaw. It builds an oval-shaped nest that measures about 23 centimetres (9.1 in) across, either near the breeding lake or on vegetation emerging from it. The black-throated loon usually lays a clutch of two, rarely one or three, brown-green eggs with dark splotches. After an incubation period of 27 to 29 days, the chick hatches, and is fed a diet of small fish and invertebrates. This contrasts with the mostly fish diet of the adult. To catch this food, it forages by itself or in pairs, very rarely foraging in groups. It dives from the water, going no deeper than 5 metres (16 ft). Most dives are successful. Whether or not at least one chick will hatch from a nest is variable, ranging from 30% to 90%. Most failures come from predators and flooding. Overall, the population of this loon is declining, although the
Taxonomy and etymology
The black-throated loon, Gavia arctica, was originally described by
There are two subspecies:
- Gavia arctica arctica (Linnaeus, 1758) – This subspecies is found in northern Europe, east to the center of Lena River and Transbaikal. It migrates to the coasts of northwestern Europe and the coasts of the Mediterranean, Black, and Caspian Seas.[7]
- G. a. viridigularis Dwight, 1918 – This subspecies is found in eastern Russia from the Lena River and Transbaikal east to the peninsulas of Chukotka and Kamchatka and the northern portion of Sakhalin. It migrates to the northwestern Pacific coasts.[7]
G. a. viridigularis was considered to be a separate species when described by
Description
The adult black-throated loon is 58 to 73 cm (23 to 29 in) in length with a 100 to 130 cm (39 to 51 in) wingspan and a weight of 1.3 to 3.4 kilograms (2.9 to 7.5 lb). The
The non-breeding adult differs from the breeding adult in that the cap and the back of the neck are more brownish. The non-breeding adult also lacks the patterned upperparts of the breeding adult, although some of the upperwing coverts do not lose their white spots. This results in the upperparts being an almost unpatterned black from above. The sides of the throat are usually darker at the white border separating the sides of the throat and the front of the throat; most of the time a thin dark necklace between these two areas can be seen. There is white on the sides of the head that are below the eye. The bill is a steel-grey with, similar to the breeding adult, a blackish tip.[7]
The juvenile is similar to the non-breeding adult, but has a browner appearance. It has a buffy scaling on the upperparts that is especially pronounced on the scapulars. The lower face and front of the neck has a diffused brownish tinge. The juvenile does not have the white spots on the wing coverts, and its irides are darker and more dull in colour. The chick hatches with down feathers that range in colour from sooty-brown to brownish-grey, usually with a slightly paler head. The abdomen is pale.[7]
The black-throated loon can be distinguished from the Pacific loon by the white on the flanks of the former.[13]
Vocalizations
The male, when breeding, vocalizes a loud and rhythmic "oooéé-cu-cloooéé-cu-cloooéé-cu-cluuéé" whistling song. A "áááh-oo" wail can also be heard, and a growling or croaking "knarr-knor", a sound given especially at night. The alarm call at the nest is a rising "uweek".[7]
Distribution and habitat
The black-throated loon has a large range, breeding taking place across northern Europe, Asia,[1] and the Seward Peninsula in Alaska.[13] When breeding, it is found in the area around isolated, deep freshwater lakes[14] larger than 0.1 square kilometres (0.039 sq mi),[15] especially those with inlets,[7] as it prefers to face only small stretches of open water.[16] When it is not breeding, this loon moves in a general southward direction and towards ice-free sea,[7] usually wintering in coasts on north-east Atlantic Ocean and those on the eastern and western Pacific Ocean, such as the coasts of Japan.[1] During this time, its habitat is usually inshore waters along sheltered coasts, although it will sometimes be found inland, in places such as the Mediterranean and Black seas.[7]
Behaviour
Like other loons, this bird takes off by pattering on a "runway" of water.[17] While flying, it makes a barking "kwow" flight call.[18]
Breeding
This species usually nests on the ground[19] within about 1 metre (3.3 ft) of the lake it breeds at.[15] This loon also sometimes nests on vegetation, like Arctophila fulva, that have emerged from lakes. The nest site is often reused the next year.[20] The nest itself is oval-shaped[19] and built mostly by the female[21] out of heaped plant material like leaves and sticks.[14] The nest measures about 23 centimetres (9.1 in) across. Families of black-throated loons often move their nest site from the original nest ponds they inhabited to wetlands nearby after the chicks reach two weeks of age. The journey is generally less than 150 metres (490 ft).[20]
In the southern portion of its range, this loon starts to breed in April, whereas in the northern parts of its range, it waits until the spring thaw,[7] when there is adequate water for it to take off in.[19] It usually arrives before the lake thaws, in the latter case.[21]
Before copulation, the female hunches its neck and swims close to the shore until it finds a suitable place and then lies down on the shore. The male sometimes adopts the same posture as the female. During this time, the only vocalization made is a one note "hum". During copulation, the male, coming ashore, mounts the female and occasionally flaps its wings loudly. After this, the male returns to the water and preens itself. The female stays ashore for a maximum of about 23 minutes and usually starts to build the nest.[21]
The black-throated loon lays a clutch of two, very rarely one or three,[7] 76 by 47 millimetres (3.0 by 1.9 in) eggs that are brown-green with darker speckles. These eggs are incubated by both parents for a period of 27 to 29 days,[14] with the female spending the most time out of the sexes incubating. During incubation, this bird turns its eggs. The interval between when they are turned is very irregular, ranging from one minute to about six hours.[21] After they hatch, the mobile young are fed by both parents for a period of weeks.[14] The chicks fledge about 60 to 65 days after hatching, and achieve sexual maturity after two to three years.[7]
Nesting success, whether or not at least one chick will hatch from any given nest, is variable year to year, the rate of success ranging from just under 30% to just more than 90%.[20] For clutches of two eggs, the average nesting success is about 50%, whereas in clutches with only one egg, this rate is about 60%.[16] The nesting success is influenced most by first, predation,[19] and second, flooding.[16] Some of the adults that lose their clutch early in the incubation period renest. Most of the time, only one chick survives to fledge, the other dying within seven days of hatching.[20] In Scotland, a study concluded that a single pair usually fledges a chick, on average, 25% of the time per year.[7] This can be increased, although, by artificial means, such as constructing rafts for loons to nest on.[22] Whether or not there is at least one chick fledged is influenced by the density of fish in the breeding lake; a lake with a higher density of fish usually reduces the chance that a pair will fledge a chick, even though this loon feeds mainly on fish. There are two factors that might contribute to this; the first being that aquatic insects, an alternative food source for chicks, are more dense when there are less fish, and the second being that a higher density of fish means more northern pike, a predator of small chicks.[23]
Feeding
A top predator in the
When it is breeding, the adult usually feeds away from the nest, foraging either at the opposite end of the breeding or at lakes near the breeding lake. When foraging for newly hatched chicks, the adult forages in the lake where the nest is or in nearby lakes, returning after a prey item has been caught. When the chicks are older, they usually accompany both of the parents, swimming a few metres behind them. The strategy that predominates immediately after hatching is generally still employed when the chicks are older, but at a reduced rate.[29] The chicks are fed only one item of prey at a time. The young are also able to capture food themselves at least 36 days after hatching, although they are still fed daily up until about 70 days of age.[21]
The diet of black-throated loon chicks varies, the prey in the breeding lake being a major factor. For the first eight days, chicks are usually fed
Predators and parasites
The black-throated loon is sometimes parasitized by
Status
Conservation
Despite the fact that its population is declining, the black-throated loon is listed as a species of
Threats
References
Citations
- ^ . Retrieved 13 November 2021.
- ^ Linnaeus, Carl (1758). Systema naturae per regna tria naturae, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata (in Latin). Holmiae [Stockholm]: Laurentii Salvii.
- JSTOR 4068646.
- ISBN 978-0-8032-2566-4.
- ISBN 978-1-4081-2501-4.
- ^ Jobling, James A. del Hoyo, Josep; Elliott, Andrew; Sargatal, Jordi; Christie, David A.; de Juana, Eduardo (eds.). "Key to Scientific Names in Ornithology". Handbook of the Birds of the World Alive. Barcelona: Lynx Edicions. Retrieved 2 August 2017.
- ^ . Retrieved 28 May 2017.
- JSTOR 4072850.
- ^ JSTOR 4073044.
- ^ .
- ^ a b Sprengelmeyer, Quentin D. (2014). A phylogenetic reevaluation of the genus Gavia (Aves: Gaviiformes) using next-generation sequencing (Master of Science). Northern Michigan University.
- .
- ^ ISBN 978-0-06-112040-4.
- ^ ISBN 978-0-226-05781-1.
- ^ ISSN 0030-5685.
- ^ ISSN 0019-1019.
- ISBN 978-0-226-14867-0.
- ISBN 978-0-618-16675-6.
- ^ a b c d Petersen, Margaret R. (1979). "Nesting ecology of arctic loons". The Wilson Bulletin. 91 (4): 608–617.
- ^ .
- ^ JSTOR 3676139.
- .
- JSTOR 3676833.
- PMID 19175443.
- The Auk. 94 (3): 526–543.
- S2CID 85418857.
- ^ ISSN 0006-3657.
- . Retrieved 11 July 2017.
- ^ ISSN 0019-1019.
- PMID 886407.
- ^ "Migratory Bird Treaty Act Protected Species (10.13 List)". US Fish & Wildlife Service. Retrieved 13 July 2017.
- ^ "Species". aewa.org. Agreement on the Conservation of African-Eurasian Migratory Waterbirds.
Bibliography
- Peter (1988). Seabirds (2nd ed.). London: ISBN 978-0-7470-1410-2.
- Field Guide to the Birds of North America. Washington, DC: ISBN 978-0-7922-6877-2.
External links
- Flicker Field Guide Birds of the World Photographs
- Black-throated Diver Gavia arctica at BTO BirdFacts
- Profile Arctic Loon at avibirds.com
- Arctic Loon – A Field Guide to Birds of Armenia
- BirdLife species factsheet for Gavia arctica
- "Gavia arctica". Avibase.
- "Black-throated Diver media". Internet Bird Collection.
- Arctic Loon photo gallery at VIREO (Drexel University)
- Audio recordings of Black-throated loon on Xeno-canto.