Black-throated loon

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Black-throated loon
Plongeon arctique nid.jpg
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Gaviiformes
Family: Gaviidae
Genus: Gavia
Species: G. arctica
Binomial name
Gavia arctica
(Linnaeus, 1758)
Subspecies
  • G. a. arctica
  • G. a. viridigularis
Gavia arctica distribution map.png
Range of G. arctica      Breeding range     Wintering range

The black-throated loon (Gavia arctica) is a migratory aquatic bird found in the northern hemisphere. The species is known as an Arctic loon in North America and the black-throated diver in Eurasia. Its current name is a compromise proposed by the International Ornithological Committee.[2]

Taxonomy[edit]

The black-throated loon was one of the many species originally described by Linnaeus in his 18th-century work, Systema Naturae.[3] The genus name Gavia comes from the Latin for "sea mew", as used by ancient Roman naturalist Pliny the Elder.[4] The specific arctica is Latin for northern or arctic.[5]

Description[edit]

The adult black-throated loon is 58 to 77 cm (23 to 30 in) in length with a 100 to 130 cm (39 to 51 in) wingspan, shaped like a smaller, sleeker version of the great northern diver.[6] It has a weight of 1.3 to 3.4 kilograms (2.9 to 7.5 lb). The nominate subspecies in its alternate plumage has a grey head and hindneck, with a black throat and a large black patch on the foreneck, both of which have a soft purple gloss. The lower throat has a necklace-shaped patch of short parallel white lines. The sides of the throat have about five long parallel white lines that start at the side of the patch on the lower throat and run down to the chest, which also has a pattern of parallel white and black lines. The rest of the underparts, including the centre of the chest, are a pure white. The upperparts are blackish down to the base of the wing, where there are a few rows of high contrast white squares that cover the mantle and scapulars. There are small white spots on both the lesser and median coverts. The rest of the upperwing is a blackish colour. The underwing is paler than the upperwing, and the underwing coverts are white. The tail is blackish. The bill and legs are black, with a pale grey colour on the inner half of the legs. The toes and the webs are grey, with the latter also being flesh coloured. The irides are a deep brown-red. The sexes are alike, and the subspecies viridigularis is differentiated from the nominate by the former's green throat patch, compared to the latter's black throat patch.[7]

The non-breeding adult of the nominate 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 nominate 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]

Vocalizations[edit]

The calls include a yodelling high-pitched wail and harsh growls, similar but lower pitched than Pacific loon.

Distribution[edit]

It breeds in Eurasia and occasionally in western Alaska. It winters at sea, as well as on large lakes over a much wider range.

Behaviour[edit]

Breeding[edit]

This species can be found to habitate the area around isolated, deep freshwater lakes. It protects this territory. The nest is made on the ground, out of heaped plant material like leaves and sticks on the shores of lakes.[8]

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. The hatched, mobile young are fed by both parents for a period of weeks.[8] The chicks fledge about 60 to 65 days after hatching.[7]

Most of the time, only one chick survives to fledge, with the other dying before seven days after hatching.[9] On average, a single pair will usually fledge a chick about 25% of the time per year.[7]

Feeding[edit]

This species, like all divers, is a specialist fish-eater, catching its prey underwater. It flies with neck outstretched. It feeds on fish, insects, crustaceans and amphibians.

The young of this bird are fed invertebrates that are caught in the lake that the nest is found near or on.[9]

Miscellaneous[edit]

Breeding, top, and non-breeding, bottom, Arctic loons
Eggs, Collection Museum Wiesbaden, Germany

The black-throated diver is one of the species to which the Agreement on the Conservation of African-Eurasian Migratory Waterbirds (AEWA) applies.

Instructions for constructing and deploying artificial floating islands to provide black-throated divers with nesting opportunities are given in Hancock (2000).

In 2007, RSPB Scotland and the Scottish Natural Heritage (SNH) stated that it was surprised by an increase in the last 12 years in the breeding figures in the UK for the red-throated diver and the rarer black-throated diver of 16% and 34% respectively due to the anchoring of 58 man-made rafts in lochs. Both species decreased elsewhere in Europe.

The black-throated diver is the current school emblem of Achfary Primary School.

Dr Mark Eaton, an RSPB scientist, traced the drop in overall numbers to warming of the North Sea which reduced stocks of the fish on which they feed.[10]

References[edit]

Citations[edit]

  1. ^ BirdLife International (2012). "Gavia arctica". IUCN Red List of Threatened Species. Version 2013.2. International Union for Conservation of Nature. Retrieved 26 November 2013. 
  2. ^ Gill, F.; Wright, M.; Donsker, D., eds. (2009). "IOC World Bird List (v 2.2)". Retrieved 3 September 2009. 
  3. ^ (Latin) Linnaeus, Carl (1758). Systema naturae per regna tria naturae, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata. Holmiae [Stockholm]: Laurentii Salvii. 
  4. ^ Johnsgard, Paul A. (1987). Diving Birds of North America. University of Nevada–Lincoln. ISBN 0-8032-2566-0. 
  5. ^ Jobling, James A (2010). The Helm Dictionary of Scientific Bird Names. London: Christopher Helm. p. 53. ISBN 978-1-4081-2501-4. 
  6. ^ "Arctic Loon". enature.com. eNature. 2011. Archived from the original on 2 January 2010. 
  7. ^ a b c d e f Carboneras, C.; Garcia, E. F. J. (2017). del Hoyo, Josep; Elliott, Andrew; Sargatal, Jordi; Christie, David A.; de Juana, Eduardo, eds. "Arctic Loon (Gavia arctica)". Handbook of the Birds of the World Alive. Barcelona: Lynx Edicions. Retrieved 28 May 2017. (Subscription required (help)). 
  8. ^ a b Hauber, Mark E. (1 August 2014). The Book of Eggs: A Life-Size Guide to the Eggs of Six Hundred of the World's Bird Species. Chicago: University of Chicago Press. p. 53. ISBN 978-0-226-05781-1. 
  9. ^ a b Bergman, Robert D.; Derksen, Dirk V. (1977). "Observations on arctic and red-throated loons at Storkersen Point, Alaska". Arctic. 30 (1): 41–51. 
  10. ^ "Rise in divers mystifies experts". BBC NEWS. 7 September 2007. 

Bibliography[edit]

Identification[edit]

  • Appleby, R.H.; Madge, S.C.; Mullarney, Killian (1986). "Identification of divers in immature and winter plumages". British Birds. 79 (8): 365–391. 
  • Birch, A.; Lee, C.T. (1997). "Field identification of Arctic and Pacific Loons". Birding. 29: 106–115. 
  • Birch, A.; Lee, C.T. (1995). "Identification of the Pacific Diver - a potential vagrant to Europe". Birding World. 8: 458–466. 

External links[edit]