Montana Field Guide

The Common Loon is a large and mainly aquatic bird. Males are generally larger than females. Adult body length ranges from 71 to 92 cm (28 to 36 inches) with wingspans to 147 cm (58 inches). Weight varies ranging from 1.6 to 8 kg (3.5 to 17.6 lb.) with an average of about 3 to 4 kg (6.6 to 8.8 lb.) (McIntyre 1988, McIntyre and Barr 1997). The feet are located far back on the body and are large, webbed, and sweep to the side rather than forward under the belly. This trait makes it difficult for Common Loons to walk on land but allows more efficient swimming underwater.

Sexes are indistinguishable based on plumage. The head and neck of breeding adults are black with a green gloss. The back, wings and sides are also black. Scapulars and wing-coverts have large white markings, which is a distinctive field mark. The eye is red. Common Loons have a broad patch of vertical white stripes on the side of the neck and a smaller patch on the upper foreneck. The breast and belly are white and the bill is straight, heavy and black (McIntyre and Barr 1997). In the non-breeding plumage, the head, neck and upper parts are dark gray to dark brown. The cheeks, throat, and underparts are white. The bill is brownish-gray to pale bluish-gray or horn colored. The iris is brown. The tail is dark brown, tipped with white (Bent 1919, Johnsgard 1987, McIntyre 1986, 1988). Juvenile plumage is similar to the adult non-breeding plumage, although the upperparts have the most pale and more conspicuous feather margins than those of adults, and the throat and sides of the neck are more finely streaked with brown. This plumage is worn until the following summer when the birds molt into more adult-like basic plumage (Palmer 1962, McIntyre 1988).

Common Loons are known for their distinctive calls, three of which are heard on summer breeding lakes. The wail, a long almost mournful cry, the tremolo, a high pitched, rapid, five-beat call, and probably the best known is the yodel which is given only by males during territorial confrontations. Common Loons generally lay 2 subelliptical to ovoid shaped eggs which vary from deep olive to light brown in color, with irregular dark brown or black spots.

For a comprehensive review of the conservation status, habitat use, and ecology of this and other Montana bird species, please see Marks et al. 2016, Birds of Montana.

The Common Loon is a large loon with a heavy, black bill and an easily recognizable breeding plumage. The large size of the Common Loon distinguishes it from the Pacific Loon (G. pacifica) and the Red-throated Loon (G. stellata), as well as the Arctic Loon (G. arctica), which has never occurred in Montana. Only the Yellow-billed Loon (G. adamsii) is comparable in size. It, however, has a distinctive yellow bill as well as subtle differences in plumage (McIntyre and Barr 1997).

In Montana, spring migration begins in early to mid-March. Fall migration starts in late August and may continue through October in Montana. Transient sightings occur throughout the state during spring migration, especially between April and June, and fall migration, between September and November (Montana Bird Distribution Committee 2012). The species is not known to remain on breeding lakes throughout the year, although there are observations of Common Loons remaining in Montana throughout the winter.

In Montana, Common Loons will not generally nest on lakes less than about 13 acres in size or over 5000 feet in elevation (Skaar 1990). Successful nesting requires both nesting sites and nursery areas. Small islands are preferred for nesting, but herbaceous shoreline areas, especially promontories, are also selected. Nursery areas are very often sheltered, shallow coves with abundant small fish and insects (Skaar 1990). Most Montana lakes inhabited by Common Loons are relatively oligotrophic and have not experienced significant siltation or other hydrological changes.

The quantity and quality of nesting habitat limits the Common Loon population of northwest Montana. Skaar (1990) estimated the state's "carrying capacity" at 185 potential nesting territories, based on the size and number of lakes within the species' breeding distribution. He assumed 100 ha of surface area per pair. Kelly (1992) documented a density of 72.2 surface ha of water per adult Common Loon for the Tobacco, Stillwater, Clearwater, and Swan River drainages.

No food habit data is available for Montana. Generally, Common Loons dive from the surface and feed mainly on fishes but are opportunistic and will eat any suitable prey they can readily see and capture (McIntyre 1988) including amphibians and various invertebrates (Terres 1980). Their primary food on breeding lakes is yellow perch (Perca flavescens), followed by other shallow, warmwater fish and minnows (Cyprinidae) (Olson and Marshall 1952, Palmer 1962, Barr 1973, McIntyre 1986). Salmonids are taken on lakes that have low populations of other fish species (McIntyre 1988). On the Great Lakes, alewives (Alosa pseudoharengus) appear to be the most common prey item (McIntyre 1988). Crustaceans, especially crayfish (Decapoda), are commonly taken, and plant material is occasionally eaten (Palmer 1962, McIntyre 1988). On lakes without fish, Common Loons have been reported feeding on molluscs, insects, amphipods and amphibians (Munro 1945, Parker 1985). Young birds have a diversified diet consisting primarily of small fish and minnows, aquatic insects and crayfish (McIntyre 1988).

Winter foods are reported to include flounder (Pleuronectoidei), rock cod (Gadus morhua), herring (Clupea spp.), menhaden (Brevoortia patronus), sea trout (Salmo spp.), sculpin (Leptocottus armatus), and crabs (Palmer 1962, McIntyre 1988). A detailed study of winter-feeding patterns and preferences has not been conducted.

If nesting on a small lake, they may use an adjacent lake for supplementary foraging (Johnsgard 1987). In Ontario, Common Loons attempting to raise a chick on a fishless, acidic lake fed the chick benthic algae and possibly benthic invertebrates, but flew to other lakes to feed themselves (Alvo et al. 1988). They feed usually in waters less than 5 m deep.

In 1985, Montana's population was estimated at at least 105 birds (Skaar 1986). No other information is available for the state. Other ecological data, from different areas in the species' range, indicate lakes smaller than 80 ha generally support only one breeding pair. Typically, territory size is larger on large lakes than on small lakes. Wintering birds may defend feeding territories during the day, and gather into rafts at night. The ecology of wintering Common Loons is not well studied. McIntyre (1978) found that loons off the Virginia coast maintained individual feeding territories of four to eight ha during the day and rafted together at night. Activity patterns were significantly correlated with tidal changes. Maintenance behavior was greatest during the mid-period of tidal rise. Feeding activities peaked late in the flood tide and during the first half of the ebb tide.

In Rhode Island, no winter-feeding territories, feeding assemblages, or tide-correlated activity patterns were noted by Daub (1989).

Up to 86 lakes in Montana have had at least one pair of Common Loons present during the breeding season and up to 33 lakes have had Common Loon chicks present. On an annual basis, about 160 to 180 Common Loons can be found on Montana lakes. Between 1999 and 2001, 60% to 80% of these adults formed territorial pairs, but less than half produced chicks (Bissell 2002). Chick production in Montana has ranged between 33 and 51 chicks, with an average of 39.5 chicks produced per year. Average clutch size is 1.87 and the average chicks per successful nest (1982 to 1985) was 1.39 (Skaar 1986).

Most other reproductive data collected on Common Loons comes from studies in other areas of the species' range. These studies indicate the timing of spring arrival is correlated with latitude and dictated primarily by ice-out phenology (McIntyre 1988). Males typically return first, especially in southern breeding areas (McIntyre 1975, 1988; Sutcliffe 1980). However, pairs often arrive together at northern lakes (McIntyre 1988). Territories are established immediately after arrival and may change in size as the breeding season progresses, expanding after the chicks hatch and shrinking for failed pairs (McIntyre 1988).

Courtship begins shortly after territory reoccupation and involves quiet, shared displays including simultaneous swimming, head posturing, and short dives. Vocalizations are not extensive. Copulation sequences are stereotyped, typically last from three to ten minutes, and take place on land (McIntyre 1988). Some copulation sites become nest sites (McIntyre 1975). It is believed that pairs re-mate each spring and that courtship serves primarily to renew the pair bond (McIntyre 1988). Nest-building is conducted by both members of the pair and may immediately follow copulation, sometimes lasting over four days (McIntyre 1975, 1988). Egg laying begins one to 4.5 weeks after spring arrival and eggs are typically laid at two-day intervals (McIntyre 1975). Most clutches contain two eggs, and most one-egg clutches result from loss of the first egg (McIntyre 1975, Titus and VanDruff 1981). Both pair members incubate, beginning with the laying of the first egg, for an average period of 28 to 29 days, ranging from 26 to 31 days (Bent 1919, Olson and Marshall 1952, Palmer 1962, McIntyre 1975). An adult is present at the nest 99 percent of the time, and the eggs hatch within a day of one another (McIntyre 1975).

Chicks leave the nest within 24 hours of hatching and are soon moved to nursery areas (McIntyre 1988). Chicks are fed largely by their parents until eight weeks of age (McIntyre 1988) even though chicks are capable of short dives at the time of nest departure and may capture some fish by the second or third week (McIntyre 1975). Adults aggressively defend chicks underwater and on the surface (McIntyre 1988). Most juveniles are capable of flight at 11 to 12 weeks (Barr 1973, McIntyre 1975), and some leave their small, natal lakes or parental territories shortly afterwards (McIntyre 1975).

Common Loons appear to be faithful to breeding territories. Banded adults have been recaptured on the same breeding territory in subsequent years (McIntyre 1974, Yonge 1981). Yearly reuse of nest sites and nursery areas has been documented (Strong et al. 1987, Jung 1991), but it is not known whether the same individuals were involved. Sonograms of yodel calls suggest that individual males return to the same territory each year (McIntyre 1988, Miller 1989). Little is known about mate fidelity of breeding pairs.

You can access a variety of detailed information on Common Loons and their management in Montana in the Conservation Plan for the Common Loon in Montana (Hammond 2009).

Management of Common Loons and their habitat in Montana should include multiple methods and techniques based on the management intensity level necessary on a particular lake or area. These techniques include, but are not limited to, monitoring, protection from disturbance by people, and protection of nesting and nursery habitat.

The Montana Loon Society monitors Common Loon reproduction each year in Montana. Potential breeding lakes are visited throughout the state and observations are made of adults and chicks. Observing Common Loons on lakes throughout Montana is a productive and valuable method of monitoring, but only reveals limited information; use of the lake and the production of chicks. More intensive monitoring should be implemented in areas where Common Loons are known to occur but have low nest success. This increased monitoring activity would reveal valuable information regarding nesting attempts and the timing and causes of nest failure or chick loss (Dolan 1994). Lakes where no evidence of breeding exists, but Common Loons are present, should be monitored in the spring for any sign of nesting. This added measure would assist in determining the cause of failure at these locations and would also provide a better estimate of total breeding pairs in Montana and rates of success in the population (Dolan 1994). Additional monitoring efforts should be focused on effectiveness of signs in nesting areas and nurseries. Posting floating signs is an effective management method to protect Common Loon nesting sites and nursery areas from disturbance by people. Placing informative signs in key public areas, such as boat ramps, detailing the function and reason for floating signs, and issuing press releases about Common Loons and chick sensitivity during the breeding season, are both important aspects of floating sign success or failure (Dolan 1994).

Management methods that would protect nesting and nursery habitat are varied in scope depending on the location within the state and the particular situation. Primary to the continued use of Montana lakes by Common Loons is the protection of nesting and nursery habitat from destruction resulting from construction, dredging, or filling. Avoiding artificial water level fluctuations is another technique in protecting nest site habitat. Keep water levels consistent and only allow flooding or drawdown practices to occur after the breeding cycle has been completed.

Other ways of protecting Common Loon habitat include implementing no-wake zones to prevent erosion of nesting habitat and working with homeowner associations and other owners, thereby allowing the public to become active in the protection of Common Loons and loon habitat on their lake (Dolan 1994). Common Loons are listed as a sensitive species by the U.S. Fish and Wildlife Service, Region 1 and they are a Species of Management Concern in Region 6 (USFWS 1995).