Loon ID in Fall and Winter

by Ron Pittaway and Michael King

Adult Pacific Loon molting from breeding to winter plumage on 1 November 2011 at Oshawa.

Revised February 2014. First published in OFO News 16(3):6-7, October 1998.

Every fall a few confusing small loons are seen whose identity stirs up debate among birders. Are they Pacific, Red-throated or just small Common Loons? In this article, we discuss the fine points of identifying small loons in juvenile and winter plumages.

Ontario Status

The Common Loon is Ontario's provincial bird. It is a common breeder in cottage country and northern Ontario and a common migrant on the Great Lakes.

The Red-throated Loon is a rare breeder along the Hudson Bay coast in northern Ontario. It is a rare to uncommon migrant in southern Ontario, but large numbers are sometimes seen.

The Pacific Loon breeds sparsely in Ontario along the Hudson Bay coast. It is a prized find in southern Ontario. The American Ornithologists' Union split the Pacific Loon from the Arctic Loon in 1985. The Arctic Loon of Eurasia is not treated in this article because there are no records of it close to Ontario.

Figure 1. Common Loon: adult (top left) and small juvenile (top right) Pacific Loon: adult (middle left) and two juveniles (head and middle right), Red-throated Loon: adult (bottom left) and juvenile (bottom right) by Michael King.

Fall Migration

Adult loons generally migrate before the juveniles, but there is considerable overlap. The first adult Common Loons return to Lake Ontario in mid-August, joining the few nonbreeders in various plumages that have summered there. Adult Common Loon migration continues through September and October into November. Juveniles start appearing on Lake Ontario in late September and are common through October into November. Most Common Loons have left Ontario by December, but a few may linger into January.

Red-throated Loons, usually singles but sometimes flocks, can occur anytime but usually later during the migration period of the Common Loon. Up to 1200 Red-throated Loons have been seen on Lake Ontario in October and there were over 2000 along the Ottawa River near Ottawa on 12 November 1984. Big Red-throated Loon movements occur one or two days after strong cold fronts out of Hudson Bay.

The 27 fall records of Pacific Loon accepted to 2012 by the Ontario Bird Records Committee range from 16 October to 26 December. These include 11 in juvenile plumage, 19 in winter plumage, 6 molting from breeding to winter plumage, and two still in breeding plumage. Only four of the 27 fall records were away from the Great Lakes at Lake Simcoe, Niagara Falls, Waterloo, and Woodstock. There are also a small number of spring records of winter plumaged Pacific Loons in southern Ontario.

Molt, Plumage and Sex

When identifying a loon, keep in mind its plumage and molt. There are three main plumage types to consider: juveniles, molting adults and winter adults.

Molts: Most adult loons are in body molt when seen in fall in southern Ontario. A few Common Loons acquire almost full winter plumage by late September, many by mid-October and most by November, but some are still mostly in breeding plumage in late November. After migration to the winter range, adult loons molt all their primary and secondary feathers simultaneously and the birds are flightless for several weeks. Adult Common and Pacific Loons molt flight feathers from mid to late winter. Adult Red-throated Loons molt their flight feathers in late fall, soon after arrival on the wintering grounds, much earlier than other adult loons. Juvenile loons retain their full juvenile plumage until January or later before molting to first winter plumage.

Figure 2. Adult Common Loon in winter plumage with a faintly scaly back. Oshawa on 1 November 2011

Figure 3. Adult Common Loon almost completely molted into winter plumage but retaining some white spots of breeding plumage. Oshawa on 1 November 2011

Figure 4. Juvenile Common Loons have distinctly scaly backs caused by whitish feather edgings. Oshawa on 1 Nov 2011.

Figure 5. Adult Pacific Loon molting from breeding to winter plumage. White squares and spots will be molted and replaced by plain dark feathers. Oshawa on 29 October 2010.

Figure 6. Juvenile Pacific Loon with a distinctly scaly back. Ajax on 1 December 2005.

Figure 7. Adult Red-throated Loon shows a gleaming white neck and white in front of the eye. Niagara-on-the-Lake on 21 December 2005.

Figure 8. Juvenile Red-throated Loon shows gray neck and white speckles on the back forming V marks on the scapulars and wing coverts. Juveniles lack white in front of the eye. Bluffers Park, Toronto, 24 November 2015.

Plumages: Please refer to the drawings and photos. Juvenile Common and Pacific Loons have distinctly scaly backs (figure 4 and 6). Adult winter Commons have faintly scaly backs and adult winter Pacifics have plain blackish backs, but adults of both species usually retain scattered white-spotted breeding scapulars in the autumn (figures 3 and 5).

Both adult winter and juvenile Red-throated Loons have backs finely speckled with white (figures 7 and 8), whereas other loons have scaly or plain backs. In juvenile Red-throated, the white speckles on the back differ from those of winter adults: the juvenile's speckles are grayer (less pure white), longer and narrower, forming V-marks on the scapulars and wing coverts. The juvenile Red-throated's head and neck are washed with a variable amount of gray, sometimes extensively (figure 8).

Contrary to some references, Red-throated Loons in juvenile plumage never have a reddish throat patch. However, some molting juveniles can have a variable smudge on the throat suggesting the throat patch of breeding plumage.

Sexes: Male and female loons are similar in appearance in all plumages with females averaging slightly smaller.

Swimming Appearance

Keep in mind that loons (and other diving birds) can markedly alter their appearance under muscular control by raising or compressing their plumage. Extremes of the same individual often look like different birds. For example, loons swim low by sleeking or compressing their feathers. They also create the forehead bump by raising these feathers.

Common Loons are heavy set and big headed with a straight robust bill. They often have a bump on the forehead figures 2 and 3). Juveniles and winter adults have mostly pale gray bills (figures 2 and 4).

Red-throated Loons are small and paler above than other loons, normally with a sloping head profile (sometimes angular as illustrated) and pale slender uptilted bill. Usually the small head and bill are pointed upwards giving them a snakelike appearance (figures 7 and 8). Winter adults have gleaming white necks.

Pacific Loons are slightly larger than Red-throateds, but their darker coloration, thicker necks and straight bills make them look more like Common Loons. Pacifics often have a puffy rounded (cobra-like) head profile (figures 5 and 6), but some show a flat crown and angular head shape suggesting a Common Loon.

Flight Appearance

Loons fly swiftly and directly with continuous wing beats. They are hunchbacked with the head and neck extended and feet held together sole to sole projecting beyond the tail. Common Loons are heavy with large feet. Red-throated Loons are slim with a snakelike neck/head and small feet. The difference between a Common Loon and a Red-throated Loon in flight is like the difference between a Common Merganser and a Red-breasted Merganser. The flight appearance of a Pacific Loon is somewhat in between.

Pitfalls

Correctly judging a loon's size, especially a solitary loon at a distance, is very difficult without a direct comparison with another bird or object of known size. As well, a few small Common Loons of all ages occur widely throughout its range. However most identification problems arise with those juvenile Common Loons that are small in size with short bills. Caution: Red-throated Loons are sometimes misidentified as Pacifics, particularly juveniles which sometimes don't show the classic upturned head/bill appearance such as in Figure 1 (bottom right) and Figure 8.