The identification of Red-throated Loons is relatively straightforward compared to other loon species given the differences in size, structure, and plumage between this species and the four other loons occurring in B.C. Adult Red-throated Loons in breeding plumage are very distinctive and are unlikely to cause any identification difficulties during normal observation. The identification of non-breeding and immature plumages, however, is somewhat more difficult. All Red-throated Loons tend to lack the distinctive chest bulge that is shown by other loons when swimming, and are smaller and slimmer (especially the head and neck) than the other four loon species.
Non-breeding and immature Red-throated Loons are most similar to similarly-plumaged Pacific and Arctic Loons. Red-throated Loon is paler grey or grey-brown than these species, which are very dark blackish-brown or slate-grey on the upperparts, sides, flanks, and on the head and neck, although the back of the head and neck are often paler silvery-grey in Pacific Loon. Furthermore, these two species show much more limited white on the throat, lower face, and throat than non-breeding Red-throated Loon, with Pacific Loon often showing a narrow dark grey band across the upper throat (“chin strap”) that is lacking in Red-throated Loon. Immature Red-throated Loon shows more extensive grey on the face and neck than the non-breeding adult, but this is a paler and more diffuse grey that is very different from the sharply-defined dark grey of Pacific and Arctic Loons. The typical habit of Red-throated Loon in swimming with the head and bill angled slightly upward is also distinctive and is not usually matched by Pacific or Arctic Loons. Flying Red-throated Loons can be distinguished from flying Pacific Loons by their habit of drooping the head and neck when in flight, often briefly raising and then lowering it, as well as their more slender wings that are angled slightly back (wings held straighter in Pacific and Arctic Loons). Additionally, non-breeding Red-throated Loons appear much more extensively white than non-breeding Pacific and Arctis Loons when in flight, particularly on the head, neck, and underparts.
The two other species of loon in coastal B.C., Common Loon and Yellow-billed Loon, are both significantly larger and bulkier species, with heavier heads, necks, and bills than Red-throated Loon. Size and structure aside, the Common Loon is easily distinguished from Red-throated Loon during the winter months by the irregular, jagged border between the dark grey hindneck and whitish throat. Although the Yellow-billed Loon also tends to hold its head and bill angled upwards, similar to Red-throated Loon, the two species should be easily distinguished by the size and colouration of the bill (slender and dark grey in Red-throated Loon, heavy and pale yellow in Yellow-billed Loon).
| This species is silent during the winter but produces several distinct vocalizations during the breeding season. On the breeding grounds, the most commonly heard call is a drawn-out, far-carrying, hideous, wailing or shrieking gayorrwork or aarOOoa, usually given as a duet between members of a pair, that is similar in function to the commonly-heard yodels of other loon species. Other calls include a short, quack-like kark or bek that is given in flight by both sexes (sometimes building to a cackling kark kark kark karkarak karkarak), as well as several low cooing calls that are given almost exclusively by males and higher, shriller calls given by females. Source: Barr et al. (2000); Sibley (2000) |
Courtship
Courtship behaviour is poorly documented in this species and it is speculated that the pair bond may be established prior to arrival on the breeding grounds. Although this species is a monogamous breeder, a mate is sometimes replaced if one member of the pair dies early in the breeding season. Copulation occurs on land along the water’s edge.
Nest
Nest-building activities are brief (sometimes as little as 0.5 days), and this species generally prefers to reuse nest sites from previous years, sometimes waiting up to 2 weeks for spring flooding to subside and expose the previous year’s nest site. Both sexes contribute to building the nest, which averages 40-60 cm in diameter (20-30 cm inside diameter) and 2.5-5.5 cm in depth. There are two basic nest types in this species, and all nests are constructed from materials collected from the immediate vicinity of the nest (this species does not carry materials to the nest site). Some nests are little more than a ring of moss and grass that is built up around a shallow depression or scrape on the shoreline. These nests are very quick to construct. Other nests are constructed in shallow water consist of a mound of decaying vegetation, sedges, and mosses. These nests require more time to construct (up to several days) because they require the build-up of material to heights above the water’s surface (up to 20 cm above the surface). Rarely, nests are placed on man-made structures or anchored to submerged logs. Some nests are sparsely lined with dry grasses or decaying vegetation, and material is sometimes added to the nest during incubation.
Eggs
Clutches of (1) 2 (3) eggs are laid between early May and late June (primarily in May), and the incubation period is 24-31 days. Only one clutch of eggs is produced per season, although the female will sometimes lay a replacement clutch if the first clutch is lost. Eggs have been recorded in British Columbia as late as late July, but most have hatched by the end of June. Both adults incubate the eggs, but the female tends to spend more time incubating than the male. The colour of the fine- to coarse-grained, somewhat glossy eggs is variable and ranges from olive-buff or yellowish-brown to darker olive-brown or olive-green, usually with fine paler speckles and sparse larger, darker blackish or dark brown splotches and specks (larger in size at the larger end of the egg).
Young
The young are semiprecocial at hatching, but still rely on the parents for food. They leave the nest shortly after hatching and are tended by at least one parent at all times for the first 2 weeks; both parents attend to the chicks during this period, often alternating duties. Unlike other loons, the young are not carried on the back of the adult when swimming. The young occasionally return to shore during the first month of life, but this ceases at ~28 days of age. The hatchlings acquire two distinct sets of down after hatching. The youngest birds are covered in short, thick, dark dusky-grey to blackish-brown down, slightly paler on the lower cheeks, throat, foreneck, and lower throat and gradually shading to lighter grey on the belly; the iris is dark and the bill and feet are grey. Older chicks are overall paler brownish-grey with longer down, giving them a fuzzier appearance than younger birds. The young are capable of short flights at ~6 weeks and fledge at ~2 months of age, at which time they depart the natal territory and fly to the ocean. They are tended by both parents on the ocean during the day of fledging, but afterwards are completely independent. Dates for chicks and dependent young in B.C. range from late May to mid-September, with most observed in July.
Source: Douglas and Reimchen (1988); Campbell et al. (1990a); Baicich and Harrison (1997); Barr et al. (2000)
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The Red-throated Loon forages almost exclusively on marine waters throughout the year, and even breeding birds, which nest on lakes and ponds, fly to the ocean for foraging (except for some populations in northwestern B.C. which breed in alpine areas far from the ocean and forage on nearby large lakes and rivers). Most foraging occurs within 0.5 km of the shoreline in waters that are <1 m in depth, although it will occasionally forage in deeper and more exposed waters farther from shore. It forages primarily on small marine fish throughout the year, although it also consumes small amounts of marine invertebrates such as worms, leeches, and molluscs. Birds that forage in freshwater environments also consume some small aquatic insects and their larvae in addition to small freshwater fish. When hunting, this species often swims with its head submerged so that it can visually search for prey in the water. Once spotted, the loon dives and pursues the prey underwater, propelling itself with its feet. With the exception of particularly large fish, which are brought to the surface, most prey is consumed underwater.
Source: Douglas and Reimchen (1988); Barr et al. (2000)
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