New York Natural Heritage Program
Common Loon
Gavia immer (Brunnich, 1764)
Birds

Identifying Characteristics [-]
Male and female Common Loons are similar in appearance. Body length ranges from 61 to 91 cm and weight ranges from 2.5 to 6.1 kg, with males being larger and heavier than females (McIntyre and Barr 1997, Evers 2004). Common Loons go through several molt phases per year in which the plumage changes from definitive alternate (breeding) to basic (non-breeding) (McIntyre and Barr 1997, Evers 2004). ADULTS: In definitive alternate (breeding) plumage exhibited during the spring and summer, the head and neck are black with a slight greenish sheen. Around the throat is a prominent band of short, white streaks, with longer streaks on the sides of the neck. The bill is black, and the iris is red. The back is black with white squarish spots on the tip of each feather except for the tail. The spots are small on the back and rump and large on the scapular feathers. The underside is white with the uppermost sides of the breast streaked black and white. The tail is short and black. The wings are black, narrow, and pointed, with the tips of the inner secondaries and coverts possessing white spots, sometimes in pairs. The lining of the wings are white. The legs are black with the webbed feet being whitish above and black below (Palmer 1962, Jackson 1976, Johnsgard 1987, McIntyre 1988, McIntyre and Barr 1997, Schoch 2002, Evers 2004). In basic (non-breeding) plumage exhibited during the fall and winter, the bill is grayish with a little black on the top portion. The entire body plumage becomes grayish-brown. The underbelly remains white and continues up the front of the neck to the chin. The tail feathers are dark brown with white tips (Bent 1919, Johnsgard 1987, McIntyre 1988, McIntyre and Barr 1997, Schoch 2002, Evers 2004). JUVENILES: At the time of hatching, chicks are covered with blackish down with a white underbelly. They gradually molt and acquire their juvenile plumage, which resembles the adult basic non-breeding plumage with a few subtleties: The back and scapular feathers are rounded and have pale edges, the bill is gray, and the tips of the tail feathers are grayish-brown instead of white (McIntyre 1988, McIntyre and Barr 1997, Schoch 2002, Evers 2004). NESTS: Nests are almost always built near the water's edge on lake shores or islands in areas that are sheltered from the wind (McIntyre and Barr 1997, Evers 2004). Floating sphagnum mats and hummocks are also utilized, along with tops of beaver lodges or muskrat dens (Sutcliffe 1980, McIntyre and Barr 1997, Evers 2004). Artificial nesting platforms can be used as well (McIntyre and Barr 1997). Nest materials consist of nearby vegetation and are somewhat bowl shaped. Nests are large with outside diameters ranging from 50-60 cm (Olson and Marshall 1952, McIntyre and Barr 1997). Nests can be reused in following years with new nest material being added (McIntyre and Barr 1997). EGGS: The eggs are oval to subelliptical in shape and the color varies from dark olive to light brown with irregular dark spots (McIntyre and Barr 1997). Average dimensions for New York loon eggs are 91 x 57 mm (McIntyre 1988). VOCALIZATIONS: Common Loons have a variety of vocalizations. The most commonly known are the yodel, given only by the male to indicate territory establishment, the wail (similar to the howling of a wolf), expressing the need for the loons to move closer together, and tremolo or laughing call, which is often produced in times of disturbance. Calling primarily takes place at night and is usually a combination of the above sounds (McIntyre and Barr 1997, Schoch 2002). Daytime tremolo calls are typically given when there is human disturbance nearby (McIntyre and Barr 1997, Schoch 2002).

Characters Most Useful for Identification [-]
Their generally large size, thick, heavy bill and unique black and white plumage distinguishes the Common Loon from other waterbirds.

Best Life Stage for Proper Identification [-]
Adults in breeding plumage.

Behavior [-]
The Common Loon is highly adapted to aquatic living. They have thick dense bones that act as ballast when diving; however, this makes taking off from land unattainable. Loons require long runways in open water, usually 30 to 200 m for take off, and may become stranded on ice- covered lakes. The loons' webbed feet are also adapted for life in the water being located towards the posterior of the body to aid in swimming and diving. This tradeoff makes walking on land difficult. While day- old chicks are able to walk upright, they quickly lose this ability and by three weeks of age, juveniles assume the posture of the adults. Adults rarely come to shore except to mate and nest. Loons establish pair bonds for the season. Courtship displays are subtle and quiet and consist of head turns with the bill pointed downward and short simultaneous dives (McIntyre and Barr 1997). The males select the location of the nest site and birds having more years of experience in a particular territory had higher levels of nest success (Piper et al. 2008). Loons are thought to nest on the edge of deep water so they can slip into the water inconspicuously if threatened by a predator (Schoch 2002). Studies have shown that nests on islands, floating vegetation, or floating artificial structures increase reproductive success compared with shoreline locations where potential predators have easier targets (McIntyre and Barr 1997). Nests are constructed of wet, matted vegetation, and successful nesting locations and nests may be reused from year to year. Chicks are semiprecocial at hatching and able to leave the nest the first day. They often catch a ride on their parents' backs although they are active and able to swim. Chicks are brooded and fed by both parents and reared in a sheltered nursery area of the lake (Schoch 2002). Adult loons are territorial for the breeding season and spend the majority of their time alone or in pairs. However, for a brief time at the end of summer loons begin to stage up for migration and may be seen gathered in flocks of 10-20 individuals (Schoch 2002). Upon returning from over-wintering along the coast, loons migrating to breeding grounds in the Adirondacks arrive first on large lakes such as Lake Champlain. They will spend part of the spring there, making excursions to smaller breeding lakes and ponds as the ice melts before generally returning (80% of individuals) to establish breeding territories on the same lake every year (Evers 2001, Schoch 2002). Breeding territories may be very large, approaching 80 ha. Large lakes may support multiple pairs while smaller lakes less than 7 ha may also be used and more than one lake may be defended. Loons frequently defend both a smaller breeding lake and other adjacent lakes which constitutes the entire territory (Piper et al. 1997). Common Loons are highly territorial among conspecifics and also may attack other loons and waterfowl including grebes and Common Mergansers (Schoch 2002). Productivity appears to be density dependent. Lower density loon populations such as New York's (McIntyre 1988) often have higher productivity rates than populations at higher densities. The productivity rate of Adirondack loons in 1984-85 averaged 0.96 fledglings/nesting pair, one of the highest rates in North America with about 53% of the nests fledging young (Trivelpiece et al. 1979, Parker et al. 1986).

Diet [-]
The Common Loon's diet consists almost entirely of fish, but also includes crustaceans (especially crayfish), and aquatic invertebrates. Loons are visual feeders, diving for their food and opportunistically taking prey that are the easiest to catch and most abundant (Schoch 2002). On breeding lakes, one of the primary foods is the Yellow Perch (Perca flavescens), followed by other warm water fish and minnows (Cyprinidae) (McIntyre 1986). Adults feed their chicks small crayfish, sunfish, and minnows. On the Great Lakes, alewives (Alosa pseudoharengus) appear to be the most common prey item. In the winter, loons are reported to eat flounder, herring, and crustaceans (McIntyre 1988). Acid deposition reduces prey abundance for loons and mobilizes heavy metals into the food chain. However, decreasing pH also increases water transparency which likely contributes to higher foraging efficiency (Evers 2004). Studies on breeding lakes in Ontario have documented that fledging success is highly unlikely at a lake pH of 4.0-4.3, and high brood mortality occurs at pH levels of 4.4-5.8 (especially on smaller lakes). About a third of the lakes in the Adirondacks have pH levels below 5.6, mainly in the western part of the park where acid rain is most intense and the neutralizing capacity of the substrate is lowest (Jenkins and Keal 2004). Loons are particularly susceptible to mercury poisoning through food chain biomagnification. The concentration of methylmercury in a large yellow perch may be up to 20 million times the concentration in the water, and the concentration of methylmercury in a loon is about 10 times that of its prey. In sampled Adirondack lakes, the average level of mercury in older Yellow Perch was approximately 1.0 ppm, a level considered to be hazardous (Jenkins and Keal 2004).
Common Loon Images
click to enlarge
The Best Time to See
Summer in the Adirondack Park is the best time to see loons in New York. They can be found on many of the lakes in western Essex, northern Herkimer and Hamilton Counties, and southern Franklin and St. Lawrence Counties during peak nesting season, which is typically June and July (McIntyre and Barr 1997, Evers 2004). The birds arrive from their wintering grounds in late March and April, heading for large lakes with open water, since many of the breeding lakes can still be covered with ice. After ice out, they return to their breeding lakes and remain there until just before the lakes freeze (Schoch 2002). The birds begin their migration back to their wintering grounds in the fall between October and November. The migration routes of Common Loons from more northerly parts of their range in the upper Midwest and Canada take them over Lakes Erie and Ontario and the Finger Lakes region of New York (Schoch 2002, Evers 2004). Common Loons are often spotted overwintering off the coast of Long Island (Evers 2004).
J F M A M J J A S O N D
Present Breeding Eggs present outside adult
The time of year you would expect to find Common Loon present (blue shading), breeding (green shading) and eggs present outside adult (orange shading) in New York.
Similar Species
  • Red-Necked Grebe (Podiceps grisegena)
    Could be confused with wintering loons as plumage is similar, but loons are 2-3 times larger.
  • Double-Crested Cormorant (Phalacrocorax auritus)
    Adult Cormorants are all black, and have a very stiff tail that stands upright when swimming.
  • Common Merganser (Mergus merganser)
    Adult mergansers are only about 1/3 to 1/4 the size of loons and usually swim along the shoreline in groups.
  • Red-Throated Loon (Gavia stellata)
    Could be confused with wintering Common Loons as plumage is somewhat similar, however the Common Loon's bill is much thicker and heavier.
  • Yellow-Billed Loon (Gavia adamsii)
    The Common Loon's closest relative breeds exclusively in the high Arctic and winters along the Pacific coast.