White-billed Diver, Yellow-billed loon (Gavia adamsii)
Tory Island 13-05-2018
[order] Gaviiformes | [family] Gaviidae | [latin] Gavia adamsii | [UK] White-billed Diver / Yellow-Billed Loon | [FR] Plongeon à bec blanc | [DE] Gelbschnabeltaucher | [ES] Colimbo de Adams | [IT] Strolaga beccogiallo | [NL] Geelsnavelduiker
spanwidth min.: 135 cm
spanwidth max.: 150 cm
size min.: 77 cm
size max.: 90 cm
incubation min.: 24 days
incubation max.: 25 days
fledging min.: 70 days
fledging max.: 77 days
eggs min.: 1
eggs max.: 3
Distinguished from other four loon species by the color of its bill, which is yellow in breeding plumage and pale yellow to ivory in wintering plumage. Breeding plumage has black upper parts with striking white spots, black head and neck with purple and green gloss, and white chest and abdomen; non-breeding plumage is gray-brown. In all plumages, top part of culmen (ridge of upper mandible) is yellow and distinguishable from other species of loon. Like other loons, this species has a highly modified leg and pelvis structure well-adapted for swimming and diving but allowing almost no ability to walk; therefore, loons place nests at the water's edge and must take flight from wate
Nests in low-lying treeless tundra regions, usually coastal, at around 62-74 degrees latitude on larger, clear, low-rimmed lakes. Breeding sites may also be on inland lakes or large river deltas with untapped lakes. Requires nesting and brood-rearing lakes that are large enough to allow easy take-off from open water; form an icefree moat around shore in early spring; have clear water supporting a substantial overwintering population of small fishes; have segments of gently sloping shoreline in which nesting and brooding occurs; and have sheltered, vegetated areas, where young chicks rest and take refuge during disturbances. Nests placed at the water's edge, typically in a low, gently sloping area. Deep open water with islands is a preferred habitat for nesting relative to its availability. Most nests are placed on the leeward lake or island shore.
Gavia arctica is a widespread breeder across much of northern Europe, which accounts for less than a quarter of its global breeding range. Its European breeding population is relatively small (30%) overall. Consequently, it is provisionally evaluated as Vulnerable.
This bird is breeding in the arctic and boreal regions of Eurasia. The breeding population of the European Union, entirely restricted to Scotland, amounts to 150-160 breeding pairs and seems stable (Tucker & Heath). Elsewhere this species is decreasing due to habitat changes, increasing disturbance by humans, predation, decreasing fish populations following over-fishing and acid rains and oil pollution at sea.
Breeds in northern Scotland and the Hebrides, over much of Scandinvia and the Baltic States and across Russia to Sakhalin and Kamchatka, probably also northern China. Breeds in western Alaska but range unclear due to similarity of this species and recently split Pacific Diver G. pacifica. In winter ranges from the Baltic south to Biscay, the northern Adriatic and Black and Caspian Seas and a vagrant on the North African coast and the Canary Islands. In the far east winters off Japan, China and Taiwan. May also occur on Atlantic coast of North America.
Forages in deep open water by repeated, lengthy dives. An opportunistic forager, takes prey in relation to availability and ease of capture, and consumes underwater. Chicks are fed small, minnow-sized fish. Important prey species include ninespine stickleback, least cisco, Alaska blackfish, fourhorn sculpin, isopods and amphipods
Pair formation occurs upon arrival on breeding territory; nests are constructed early to mid-June. Nests comprised of peat, pendant grass, sedges and sometimes lined with other vegetation. Nests from previous years frequently reused. Eggs are laid in June-July (some July nests represent renestings after loss of eggs). First nests generally are in mid-June in arctic Alaska, but peak nesting may be delayed by late ice melt on lakes. Clutch size: 2. Incubation, by both sexes, lasts 27-28 days. Chicks are dry and active within hours of hatching; brooding by both parents occurs in nest for about 3 days, then little on-shore brooding after about 9 days. In some areas, chicks 9-16 days old observed riding on parents back. Adults forage to feed young for up to 45 days. Reproductive maturity probably reached at or after 4 years.
Migratory. Like Great Northern Diver, breeds on high latitude fresh waters but winters on salt water. Freshwater arrivals and departures linked to thawing and freezing; at sea mainly October-May; when late thaw breeding lakes not re-occupied until late June.