The red-throated diver is the smallest of the world’s four species of divers. It is easily recognized in flight by its long neck, which is kept outstretched and slightly arched downwards; the head is held with a slight upward curve. The red-throated diver’s breeding distribution is circumpolar in the Arctic, but it also lives in the northern parts of the coniferous forest region.
The red-throated diver is the smallest and most slender of the four species of divers in the world. It is 53–69 cm in length and weighs 1400–1900 g.
This species is easily recognized in flight by its long neck, which is kept outstretched and slightly arched downwards, while the head is held with a slight upward curve. The sexes are virtually identical in their outward appearance. The bill is dark and slightly upturned. In breeding plumage the neck and head are grey and the back of the neck has distinct black and white lengthwise stripes, the throat is red-brown, the back and the wings are dark grey-brown with small white speckles and the under-parts are white. At a distance the red-brown throat may look black. The winter plumage is lighter with grey-brown upper-parts while the throat, sides of the neck and under-parts are white. The young resemble the adult birds in winter plumage.
In flight, the red-throated diver emits a loud and monotonous cackling, ”kah kah kah…”, and when sitting on the water it emits a high wailing ”eeaaooh”.
The red-throated diver’s breeding distribution is circumpolar in the Arctic; it also lives in the northern parts of the coniferous forest region. It is found in North-America, Greenland, Iceland, Scandinavia and northern Russia.
The species breeds over most of Svalbard, but nest densities are highest in the western parts of Spitsbergen, on Bjørnøya and within Tusenøyane. It nests on small islands in freshwater lakes, ponds and lagoons as well as along their shorelines. Red-throated divers prefer open, flat tundra areas, and this habitat is mainly found along the coast in Svalbard. While waiting for the ice to break up on the lakes in spring, the divers remain at sea.
Red-throated divers arrive in Svalbard in May-June and leave in September–October. They winter in more southerly areas along coasts, in bays, and sometimes on lakes, at times in large, loosely scattered gatherings, but more often they are seen singly or in small groups.
Red-throated divers are solitary breeders, but may form loose colonies.
The nest is usually built on a small island, on a narrow point of land or on the edge of a pond. It is often situated less than half a metre from the water, so that the incubating bird can easily glide into the water if disturbed. The red-throated diver moves relatively clumsily on land because its legs are very far back on its body. It is somewhat more gregarious than the other divers, but still shows strong territorial behaviour both in flight over its territory and on the water. Although they breed in freshwater, the adults often spend considerable amounts of time at sea during the breeding season.
The red-throated diver feeds mainly on fish; the details of its feeding ecology have not been well studied in Svalbard. To catch food they dive with a smooth, neat ‘bow’, often remaining submerged for a minute or more. They can travel significant distances under water. They eat plant material and invertebrates on land in addition to fish. Parent birds feed their young with small crustaceans and aquatic insects immediately after hatching, and later switch over to feeding them fish.
Life history and reproduction
The red-throated diver’s nest is a shallow cup lined casually with plant material. They require a stable water level to nest successfully.
The olive-green eggs (clutch size ranges from one to three) are laid towards the end of June or during the first part of July, because the ice usually does not come off Arctic lakes until this time. The eggs are incubated alternately by both parents for 26–28 days, and both parents take part in caring for the chicks.
The young, which have a uniform dark grey-brown colour, are cared for by the parents until they fledge at an age of six to seven weeks.
Management status and monitoring
The number of red-throated divers in Svalbard is not known with certainty, but there are probably between 500–1000 breeding pairs. The European breeding population declined sharply in the 1970s and 80s, but has subsequently shown recovery and is now estimated to be 92000 pairs.
This species is very shy during the breeding season and is vulnerable to disturbance. Photographers and other intruders approaching too closely can easily disrupt nesting. Unattended eggs are quickly preyed upon by arctic foxes, glaucous gulls or great skuas.