Black-throated Diver
The Black-throated Diver, known as the Black-throated Loon or Arctic Loon in north America, is an aquatic bird of the diver family found in the Northern Hemisphere.
The adult Black-throated Diver is 23 to 30 inches in length with a 39 to 51 inches wingspan and it is shaped like a smaller, sleeker version of the Great Northern Diver.
The breeding adult 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 5 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. The sexes are alike.
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 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.
The Black-throated Diver breeds in Eurasia and occasionally in western Alaska. It winters at sea as well as on large lakes over a much wider range. In the UK, the Black-throated Diver can be found on lochs in the Scottish Highlands in summer and around sheltered coasts in winter, especially the Moray Firth in north east Scotland, the west coast of Scotland and the north east and south west coasts of England. In addition, it is sometimes seen on inland reservoirs and lakes.
In the breeding season, the Black-throated Diver can be found on isolated, deep freshwater lakes especially those with inlets since it prefers to face small stretches of open water. It protects this territory and will often return to the site to nest near it. The oval-shaped nest is usually located within 3 feet of the body of water it nests near and is made out of heaped plant material, leaves and sticks. It also sometimes nests on vegetation that has emerged from lakes.
In the southern part of its range, the Black-throated Diver starts to breed in April whereas in the northern part of its range, it waits until the spring thaw. It will usually arrive before the lake thaws in the latter case. The Black-throated Diver lays a clutch of 2, very rarely 1 or 3, eggs which are incubated by both parents for a period of 27 to 29 days, with the female spending the most time out of the sexes incubating. The hatched, mobile chicks are fed by both parents for a period of several weeks and fledge about 60 to 65 days after hatching. Nesting success (i.e. whether or not at least a single chick will hatch from any given nest) is variable with the rate of success ranging from just under 30% to just over 90%. The nesting success is influenced primarily by predation and flooding as well as disturbance and this makes the Black-throated Diver a vulnerable as well as a rare breeding species.
The Black-throated Diver feeds on fish and sometimes insects, molluscs, crustaceans and plant matter. It usually forages by itself or in pairs but sometimes in small groups. It dives with consummate ease from the surface into the water at depths of no more than about 15 feet. These dives are frequent and most are successful. Those that are successful are usually shorter than those that are unsuccessful with an average of 17 seconds for each successful dive and 27 seconds for each unsuccessful dive. These dives usually result in only small food items being caught and those that are more profitable are usually more than 40 seconds where the bird catches quick-swimming fish. When they are breeding, the adults will usually feed away from the nest, either at the end of the breeding lake away from the nest or at lakes near the breeding lake. When foraging for newly hatched chicks, one of the adults will forage in the lake that the nest is at or in nearby lakes, returning to the nest after a prey item has been caught. When the chicks are older, they will usually accompany both of the parents, and swim a short distance behind them.
Date: 21st June 2017
Location: Loch Shin, Lairg, Highland
The adult Black-throated Diver is 23 to 30 inches in length with a 39 to 51 inches wingspan and it is shaped like a smaller, sleeker version of the Great Northern Diver.
The breeding adult 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 5 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. The sexes are alike.
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 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.
The Black-throated Diver breeds in Eurasia and occasionally in western Alaska. It winters at sea as well as on large lakes over a much wider range. In the UK, the Black-throated Diver can be found on lochs in the Scottish Highlands in summer and around sheltered coasts in winter, especially the Moray Firth in north east Scotland, the west coast of Scotland and the north east and south west coasts of England. In addition, it is sometimes seen on inland reservoirs and lakes.
In the breeding season, the Black-throated Diver can be found on isolated, deep freshwater lakes especially those with inlets since it prefers to face small stretches of open water. It protects this territory and will often return to the site to nest near it. The oval-shaped nest is usually located within 3 feet of the body of water it nests near and is made out of heaped plant material, leaves and sticks. It also sometimes nests on vegetation that has emerged from lakes.
In the southern part of its range, the Black-throated Diver starts to breed in April whereas in the northern part of its range, it waits until the spring thaw. It will usually arrive before the lake thaws in the latter case. The Black-throated Diver lays a clutch of 2, very rarely 1 or 3, eggs which are incubated by both parents for a period of 27 to 29 days, with the female spending the most time out of the sexes incubating. The hatched, mobile chicks are fed by both parents for a period of several weeks and fledge about 60 to 65 days after hatching. Nesting success (i.e. whether or not at least a single chick will hatch from any given nest) is variable with the rate of success ranging from just under 30% to just over 90%. The nesting success is influenced primarily by predation and flooding as well as disturbance and this makes the Black-throated Diver a vulnerable as well as a rare breeding species.
The Black-throated Diver feeds on fish and sometimes insects, molluscs, crustaceans and plant matter. It usually forages by itself or in pairs but sometimes in small groups. It dives with consummate ease from the surface into the water at depths of no more than about 15 feet. These dives are frequent and most are successful. Those that are successful are usually shorter than those that are unsuccessful with an average of 17 seconds for each successful dive and 27 seconds for each unsuccessful dive. These dives usually result in only small food items being caught and those that are more profitable are usually more than 40 seconds where the bird catches quick-swimming fish. When they are breeding, the adults will usually feed away from the nest, either at the end of the breeding lake away from the nest or at lakes near the breeding lake. When foraging for newly hatched chicks, one of the adults will forage in the lake that the nest is at or in nearby lakes, returning to the nest after a prey item has been caught. When the chicks are older, they will usually accompany both of the parents, and swim a short distance behind them.
Date: 21st June 2017
Location: Loch Shin, Lairg, Highland
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