Loons vary in size across their range. The smallest individuals occur in the upper Great Lakes and central Canada and they increase in size going east and west to the coasts (Evers et al. 2010). This variation in body size is related to how far the individuals must travel to their wintering grounds, with birds that travel farther being smaller than birds that have migrate shorter distances (Gray et al. 2014).
Common Loons are a species of Special Concern in New York State. Their breeding distribution within New York is restricted primarily to deep productive lakes in the Adirondacks, and although they have recovered from a notable decline since the 1970s, they remain vulnerable to persistent and ongoing threats on both their breeding and wintering ranges in the northeastern U.S. The large Adirondack population, increasing population size, and moderate threat levels contribute to the S4 rank.
The abundance of loons in New York has remained relatively stable or has slightly increased over the the past 50 years with the population fluctuating between roughly 200 and 300 breeding pairs. The current population size has rebounded back to the levels of the early 1960s after a marked decline during the 1970s. In the early 1960s, Arbib (1963) reported 120 pairs at 90 locations and estimated the population to be between 240 and 360 breeding pairs. In 1977-1978, a survey of over 300 lakes in the Adirondacks conducted by the New York State Department of Environmental Conservation found 105 territorial pairs on 83 lakes and estimated the population at fewer than 200 pairs. In 1984-1985, the New York State Department of Environmental Conservation surveyed 557 lakes in the Adirondacks and estimated the northern New York loon population at 216-270 breeding pairs (Parker et al. 1986). Since 2001, the Adirondack Center for Loon Conservation has conducted an annual census in the Adirondacks. From 2001 and 2018, between 129 and 227 lakes were surveyed with loons observed on about 75% of them.
Likewise, the distribution of loons in New York has expanded since the early 1980s. A comparison of the first and second Breeding Bird Atlases shows a 42% increase in occupancy. In the first atlas (1980-1985), loons were reported primarily from the central Adirondacks, western Adirondack Foothills, and Adirondack High Peaks. In the second atlas (2000-2005), there were reports of Common Loons in previously unreported lakes in all directions. There was an increase in the number of reports from Lake Champlain, the St. Lawrence River area, and the eastern and southern Adirondacks, extending into the eastern Adirondack Foothills. Particularly noteworthy were records of confirmed breeding in central and western New York on Chautauqua, Keuka, and Skaneateles lakes (McGowan and Corwin 2008).
Information on the historical status of loon populations in New York is lacking. Loons are believed to have been more widely distributed in the early 1800s because, in addition to the core of their range in the Adirondacks, loons most likely bred on most of the Finger Lakes and along the shores of Lake Ontario (Arbib 1963, McIntyre 1979). Shooting of adult birds and harrassment of breeding pairs in the mid- and late-1800s contributed to a severe decline (McIntyre 1979). By the turn of the century, very few Common Loons were reported in the Adirondacks (Eaton 1910). With a change of attitudes and legal protection, loon populations rebounded by the early 1960s. By the second Breeding Bird Atlas in 2000-2005, loons had expanded their range and were once again found breeding on some of the Finger Lakes (McGowan and Corwin 2008).
Although the population of breeding loons in New York is stable or slightly increasing, several threats are acting in combination to negatively affect loons in New York State. Mercury poisoning is one of the most significant threats. Elemental mercury released from sources such as waste incinerators and coal-fired power plants (mostly in the Midwest) is deposited by atmospheric currents and transformed in water bodies into methylmercury, a neurotoxin. Common Loons are particularly affected by this process because they are predators at the top of a long aquatic food chain, with increasing mercury concentration levels as you move up the food chain, a process known as bioaccumulation (Yu et al. 2011). High mercury levels in Common Loons are correlated with behavioral changes that lead to lowered reproductive success and decreased survival (Evers et al. 2008). The Adirondacks are considered a biological mercury hotspot (Evers et al. 2007), and in a long-term study found that birds with high levels of mercury fledged approximately 20% fewer chicks than loons with lower mercury levels (Schoch et al. 2014). In addition, lake acidification increases the availability of methylmercury and also leads to a decrease in the diversity and abundance of prey for loons in affected water bodies (Schoch and Evers 2002).
Other threats to loons include lead poisoning, fishing line entanglement, oil spills, human disturbance, shooting, and disease (Evers et al. 2010). Ingestion of lead fishing tackle causes lead poisoning and eventually death, and ingestion of fish hooks and entanglement in fishing line can also cause permanent injury or death. Of 105 Common Loons found dead or debilitated in New York from 1972-1999, 21% of the pathologies were attributed to ingestion of lead fishing weights, while 23% had aspergillosis (Stone and Okoniewski 2001). Oil spills pose a threat for migrating loons and wintering birds along the Atlantic coast (Evers et al. 2010). Loons are also susceptible to human disturbances on breeding lakes. These include effects of shoreline development, which leads to decreased reproductive success (Spilman et al. 2014), and disturbances caused by paddlers, campers, boaters, and jet-skiers, which can interrupt incubation and brooding and result in nest failure or abandonment. Loon nests may be affected by water fluctuations as well, which may flood nests or leave nests more vulnerable to predation. Illegal shooting along the Atlantic coast and elsewhere is a known mortality factor. Increasing numbers of predators such as raccoons, otters, and eagles also pose a threat. Common Loons are susceptible to several diseases including type C and type E botulism. Outbreaks of type E botulism, Clostridium botulinum, have occured on Lake Erie since 2000 and on Lake Ontario since 2002. An estimated 12,000 loons died on Lake Erie from botulism between 2000 and 2006 (Evers et al. 2010).
Common Loons can adapt to moderate levels of lakeshore development and recreational use, but it is important to minimize disturbance to nesting loons (Spilman 2006; Spilman et al. 2014). Disturbed incubating loons may not return to their nests for an hour or more, leaving eggs vulnerable to predation and cooling (McIntyre 1975, Titus and VanDruff 1981). Nesting areas should be located and protected. Small islands (those less than 5 ha) and deadwaters should not be developed at all, and buffer zones of 150 m should be left undisturbed on either side of mainland nest sites and deadwater entrances (Strong and Bissonette 1985). Nursery areas of lakes (shallow areas and coves where adults raise and collect food for their chicks) should also not be disturbed. Jet skis currently are the most threatening disturbance to chicks because they are fast, highly maneuverable, and able to run in shallow water where loon nests and nurseries are often located (McIntyre and Barr 1997). Motorboats may affect loons more negatively than canoes. Boat engine horsepower should be limited and speed limits should be established on smaller breeding lakes or in designated areas of larger lakes. Loons defending their territories through behaviors such as the penguin dance or vocalizations such as the tremolo (laughing call) should be given their space. Non-lead sinkers and jigs should always be used when fishing, and snagged tackle should be recovered. Human-caused water level fluctuations should be minimized, especially during the peak nesting period of mid-May to mid-July, as nests can be lost to inundation or increased exposure to predators from drawdown. Rises in water levels are more detrimental than drawdowns, especially when they occur late in the season when the loons have little possibility of re-nesting (Strong and Bissonette 1985). Artificial rafts may improve nesting success under certain conditions, such as on lakes with a breeding history experiencing fluctuating water levels and recent repeated failed nesting attempts (DeSorbo et al. 2008). In the Adirondacks, excellent natural nesting sites are available, and these are preferred over artificial nest rafts.
Considerable research has been conducted on the Common Loon, as it is an iconic species and excellent indicator of trends in environmental quality. Current research is focused on detecting population trends, effects of mercury pollution on reproductive success, and use of migratory routes and wintering areas. These efforts should be continued in order to gather information on the long-term effects of acidification, environmental pollutants, and human interactions. Population monitoring and contaminant research is being coordinated with other efforts in the Northeast to enable an assessment of the effects of mercury and other factors on northeastern loon populations. Continuing such monitoring efforts will enable the early detection of unusual changes in population levels and the implementation of appropriate management efforts as well as assist in the development of appropriate policies regarding mercury and other contaminants (Schoch and Evers 2002). The mechanism of the type E botulism outbreaks affecting migrating loons on the Great Lakes is still poorly understood; additional research is needed to determine the causes of the outbreaks and how they can be prevented or minimized (Schoch 2002). Further study is also needed on the sensitivity of loons to toxins (McIntyre and Barr 1997), ecology of wintering loons (Rimmer 1992), and life history of juveniles between the time they fledge and return to northern lakes (Holst 2005). Inexperienced juveniles apparently do not migrate with the adults and require suitable stopover waterbodies on their way to the coast. Potential impacts from climate change are poorly understood and may include an increase in the rate of mercury methylation, changes in the availability of near-shore marine fishes in the winter, and storm-induced changes in water levels on breeding lakes (Evers et al. 2010).
Common Loons breed on a wide variety of lakes and reservoirs in the Adirondacks ranging from oligotrophic (low-nutrient) to eutrophic (high-nutrient), small to large, shallow to deep, clear to turbid, and remote to heavily developed (Rimmer 1992). Breeding has been documented on lakes as small as 4 ha, but loons typically nest on lakes 20 ha or larger (McIntyre 1975). Lakes smaller than 80 ha often support only a single pair (McIntyre 1988). Common Loons often breed on lakes that contain both shallow and deep water areas. Shallow areas are important for feeding and brood rearing, and deeper areas provide escape cover for incubating adults. Nests are often located as close as possible to deep water, on the edge of an island or low hummock, or on rocks, logs, or pieces of bog mat (McIntyre 1988). Since loons are visual feeders, water clarity is also an important component of breeding habitat selection (McIntyre 1975, McIntyre 1988). Nonbreeding habitat is primarily seacoasts, bays, inlets, and estuaries, less frequently along lakes and rivers, and occasionally up to 100 km off the coast (AOU 1998).
Breeding loons are mostly restricted to the Adirondack Mountains, St. Lawrence Valley, and Lake Champlain. There are a few scattered records in the Tug Hill Plateau and in central New York. An apparent range expansion has occurred since the mid 1980s (McGowan and Corwin 2008). Especially noteworthy are the newly confirmed breeding records on Chautauqua, Keuka, and Skaneateles lakes in central and western New York. During the summer months nonbreeding loons can be found outside of the typical breeding range on large inland waterbodies and off the coast of Long Island. Migratory birds can be found throughout the state with an important flyway over the Finger Lakes and Lake Champlain. Wintering birds are typically found along the Atlantic Coast, and rarely on the Great Lakes (Levine 1998).
The breeding range of the Common Loon extends from Iceland and Greenland across Canada and the northern United States to Alaska, south to California, Montana, North Dakota, Iowa, Illinois, Indiana, Ohio, Pennsylvania, New York, southern New England, and Nova Scotia (AOU 1983). Non-breeding loons are mainly found along the Pacific coast from Aleutians to Baja California and Sonora, along the Atlantic and Gulf coasts from Newfoundland to Florida and west to Texas, and in western Palearctic along the Atlantic coast to northwestern Africa (AOU 1983). In North America, wintering Common Loons are most concentrated along the South Carolina coast, around Vancouver Island, in northern California, along the Gulf Coast adjacent to the Florida panhandle, and along the Atlantic seaboard from Massachusetts to Maine (Root 1988).
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 the 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).
Their generally large size, thick, heavy bill and unique black and white plumage distinguishes the Common Loon from other waterbirds.
Adults in breeding plumage.
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 trade-off makes walking on land difficult. While day-old chicks are able to walk upright, they quickly lose this ability; 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 have 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 stage 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 will support one pair. More than one lake may be defended by a pair. 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. Low 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 1998-2007 averaged 0.746 fledglings/nesting pair (Schoch et al. 2014).
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 on a lake with 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).
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 nesting in the Adirondacks winter along the Atlantic Coast from Massachusetts to New York (Kenow et al. 2009).
The time of year you would expect to find Common Loon active, reproducing, and eggs present outside adult in New York.
Gavia immer (Brunnich, 1764)
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Information for this guide was last updated on: July 8, 2019
Please cite this page as:
New York Natural Heritage Program. 2020. Online Conservation Guide for Gavia immer. Available from: https://guides.nynhp.org/common-loon/. Accessed September 21, 2020.