Gavia immer - (Brunnich, 1764)
Common Loon
Taxonomic Status: Accepted
Related ITIS Name(s): Gavia immer (Brunnich, 1764) (TSN 174469)
French Common Names: plongeon huard
Spanish Common Names: Colimbo Mayor
Unique Identifier: ELEMENT_GLOBAL.2.100554
Element Code: ABNBA01030
Informal Taxonomy: Animals, Vertebrates - Birds - Other Birds
Image 7563

© Larry Master

 
Kingdom Phylum Class Order Family Genus
Animalia Craniata Aves Gaviiformes Gaviidae Gavia
Genus Size: B - Very small genus (2-5 species)
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Concept Reference
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Concept Reference: American Ornithologists' Union (AOU). 1998. Check-list of North American birds. Seventh edition. American Ornithologists' Union, Washington, D.C. [as modified by subsequent supplements and corrections published in The Auk]. Also available online: http://www.aou.org/.
Concept Reference Code: B98AOU01NAUS
Name Used in Concept Reference: Gavia immer
Taxonomic Comments: Considered conspecific with G. adamsii by some authors (AOU 1983).
Conservation Status
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NatureServe Status

Global Status: G5
Global Status Last Reviewed: 07Apr2016
Global Status Last Changed: 20Nov1996
Ranking Methodology Used: Ranked by inspection
Rounded Global Status: G5 - Secure
Reasons: Still a common species in many portions of its large range but perhaps re-evaluate periodically as monitoring efforts improve.
Nation: United States
National Status: N4B,N5N (05Jan1997)
Nation: Canada
National Status: N5B,N5N,N5M (02Jan2018)

U.S. & Canada State/Province Status
Due to latency between updates made in state, provincial or other NatureServe Network databases and when they appear on NatureServe Explorer, for state or provincial information you may wish to contact the data steward in your jurisdiction to obtain the most current data. Please refer to our Distribution Data Sources to find contact information for your jurisdiction.
United States Alabama (S4N), Alaska (S5B,S4N), Arizona (S2N), Arkansas (S4N), California (S1), Colorado (SNA), Connecticut (S1B), Delaware (SNA), Florida (S5N), Georgia (S4), Idaho (S1B,S2N), Illinois (SXB,S2N), Indiana (SXB), Iowa (SXB,S4N), Kansas (S3N), Kentucky (SNA), Louisiana (S4N), Maine (S4S5B,S4S5N), Maryland (S4N), Massachusetts (S2B,S5N), Michigan (S3), Minnesota (SNRB), Mississippi (SNA), Missouri (SNRN), Montana (S3B), Navajo Nation (S2N), Nebraska (SNRN), Nevada (S2N), New Hampshire (S2B), New Jersey (S4N), New Mexico (S4N), New York (S4), North Carolina (S5N), North Dakota (S4), Ohio (SNA), Oklahoma (S3N), Oregon (SHB,S5N), Pennsylvania (SH), Rhode Island (SNA), South Carolina (SNRN), South Dakota (S1B,S3N), Tennessee (S4N), Texas (S4N), Utah (S3?N), Vermont (S3B), Virginia (SNRN), Washington (S2B,S4N), West Virginia (S1B,S4N), Wisconsin (S3B), Wyoming (S1B,S2N)
Canada Alberta (S5), British Columbia (S5B), Labrador (S5B,S5M), Manitoba (S4S5B), New Brunswick (S4B,S4M,S4N), Newfoundland Island (S5B,S4N), Northwest Territories (S4S5B), Nova Scotia (S4B,S4N), Nunavut (S5B,S5M), Ontario (S5B,S5N), Prince Edward Island (S1B,S4M), Quebec (S5B), Saskatchewan (S5B), Yukon Territory (S4B)

Other Statuses

Committee on the Status of Endangered Wildlife in Canada (COSEWIC): Not at Risk (01Apr1997)
Comments on COSEWIC: This species is widespread and relatively abundant, though subject to threats locally from recreational development, acid rain and other changes to lake conditions.

Designated Not at Risk in April 1997.

IUCN Red List Category: LC - Least concern

NatureServe Global Conservation Status Factors

Range Extent: >2,500,000 square km (greater than 1,000,000 square miles)
Range Extent Comments: Nesting occurs in Iceland, Greenland, and across Canada and the northern United States to Alaska, and south to California, Montana, the Great Lakes region, New York, New England, and Nova Scotia (AOU 1998). In winter, this loon occurs mainly 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 the western Palearctic along the Atlantic coast to northwestern Africa (AOU 1998). In North America, this species is most concentrated in winter 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).

Area of Occupancy: Unknown 4-km2 grid cells
Area of Occupancy Comments: Undetermined; Linear occupancy is unknown.

Number of Occurrences: > 300
Number of Occurrences Comments: This species is represented by a large number of occurrences.

Population Size: 100,000 - 1,000,000 individuals
Population Size Comments: In the late 1980s, there were about 500,000 in Canada, 34,000 in Alaska, 10,000 in Minnesota, and smaller (often remnant) populations in 12 other states (Ehrlich et al. 1992), including 270-300 breeding pairs in Michigan (Evers 1992).

Although no precise continentwide estimate of populations is available, some 500,000-600,000 adults probably inhabit the U.S. and Canada (J. McIntyre, pers. comm.). Several states and provinces have begun annual breeding surveys (summarized in McIntyre 1988). Estimated numbers of adults south of Canada number close to 18,000 and Alaska is thought to support about 34,000 common loons. Canada may be inhabited by half a million or more birds. Estimate of 607,000-635,000 individuals in North America and ca. 5,000 in Europe in 2006 and similar numbers (612,000-640,000) in 2012 (Wetlands International 2014).

Number of Occurrences with Good Viability/Integrity: Many to very many (41 to >125)
Viability/Integrity Comments: Likely high given large population and a breeding range from Alaska across North America to Iceland, although relatively sparse in the western U.S.

Overall Threat Impact Comments: Susceptible to human disturbance at breeding lakes (via development of shoreline areas and aquatic recreational activities), acid rain alterations of lake ecosystems, and mercury poisoning (USFWS 1987, Rimmer 1992; St. John, 1993). Also may be jeopardized in some areas by fluctuating water levels at the nest site and by increasing numbers of predators such as raccoons (Rimmer 1992).

HABITAT LOSS AND DEGRADATION: Direct and indirect effects of shoreline development may reduce the suitability of lakes for nesting. Although radical shoreline alteration and cottage construction appear to only rarely inhibit nest site selection, increased human activity around developments often does (McIntyre 1988, Sutcliffe 1980, Zimmer 1979). Hatching success decreased as the number of cottages within 150 meters of nests increased on lakes in central Ontario (Heimberger et al. 1983). McIntyre (1988) found that the number of lakes with territorial loons decreased with increasing shoreline development and recreational use in Minnesota between 1971-86. Water-level fluctuations resulting from human-made dams can also reduce the suitability of a lake for breeding. Fair (1979) documented nest abandonment and predation following lake drawdowns in New Hampshire. On Stillwater Reservoir in New York, McIntyre (1988) found that nests were lost to inundation when water levels rose more than 20 cm. Breeding loons in an area of regulated water levels in Minnesota had significantly lower productivity than other populations on naturally fluctuating lake systems (Reiser 1988). Nesting may be delayed by water levels that fail to recede after snowmelt (Fair 1979, Strong 1985). Although poorly regulated lake levels can lead to nest losses, creation of reservoirs has increased the availability of suitable nesting habitat in some areas (e.g., McIntyre 1988).

HUMAN DISTURBANCE AND HUNTING: Recreational pressures may have contributed to declines in some populations, but loons generally can acclimate to moderate recreational lake use. While Ream (1976) suggested that disturbance of nest sites by canoeists in the Boundary Waters Canoe Area in Minnesota was the primary factor limiting productivity, Titus and VanDruff (1981) later found few negative impacts from recreational activities in the Boundary Waters Canoe Area. Smith (1981) reported identical productivity on both remote lakes and on lakes with established canoe routes in Alaska. In Maine, no significant difference in breeding success was found for loons on high human-use versus low human-use lakes (Christenson 1981). However, densities may be lower on heavily developed than on relatively undeveloped lakes (McIntyre 1988).

When incubating loons leave nests because of disturbance, they may not return for an hour or more, leaving the eggs vulnerable to predation and cooling (McIntyre 1975, Titus and VanDruff 1981). Loons exhibit behavioral modifications in response to moderate recreational activity on many lakes. On high human-use lakes, loons flush at shorter distances (Smith 1981, Titus and VanDruff 1981), flush less readily and less vigorously, vocalize less once flushed, and return to the nest more quickly than loons on remote lakes (Titus and VanDruff 1981).

Motorboats may impact loons more negatively than canoes due to differences in peak use and breeding periods. On Boundary Waters Canoe Area lakes, motorboat use is heaviest early in the season, when loons are nesting, while canoe use peaks in August after the nesting season (McIntyre 1988). Loons are more easily able to avoid canoes than motorboats, and chicks are less likely to be separated from their parents by canoes. Motorboat wakes in combination with high water levels may cause nest destruction (Vermeer 1973).

Although the sport shooting that impacted populations around 1900 is now illegal, loons continue to be intentionally killed on occasion, primarily by sport and commercial fishers who consider the birds to be direct competitors (McIntyre 1988). Of 29 dead loons necropsied in New York from 1972-86, three had been shot (Okoniewiski and Stone 1987). Loons are still taken for food by American Indians and Inuits. In northern Quebec, the annual harvest ranges from 2,500-6,500 loons, most of them common loons (Desgranges and Laporte 1979). This harvest is thought to be too high to support the region's current population of 12,000 pairs.

COMPETITION: Intraspecific competition may limit productivity. Sibling aggression can be severe, especially during food shortages, and may result in the death of the subordinate, usually younger, chick (Dulin 1987). Chicks that wander into adjacent territories may be killed by neighboring adult loons (McIntyre 1988). Severe fighting by adults has been documented, presumably over territorial ownership, and can lead to injury or nest abandonment (e.g., Kaveney and Rimmer 1989). Competition with aggressive, non-native mute swans (CYGNUS OLOR) has been documented in Michigan (McPeek and Evers 1989).

ENTANGLEMENT: Mortality is known to occur from entanglement in monofilament sports fishing line and in commercial fishing nets (Vermeer 1973, Okoniewski and Stone 1987). Commercial fish traps and nets in the Great Lakes pose a serious, although unquantified, threat to loons (McIntyre 1986, 1988). Loons are also caught in nets used during coastal fishing operations (McIntyre 1978). Most mortality from these sources goes unreported.

ENVIRONMENTAL POLLUTANTS: Organochlorines and their residues have been detected in eggs and carcasses. DDE levels in tissue from Minnesota in the 1960s may have had adverse, sublethal effects (Ream 1976, McIntyre 1988). Eggs with higher levels of DDE residues tend to have thinner shells than eggs with lower residue levels (Vermeer 1973, McIntyre 1975, Sutcliffe 1978, Fox et al. 1980), although no studies have demonstrated evidence of shell breakage. There appears to be no documentation of lowered productivity as result of elevated pesticide loads (Fox et al. 1980), and organochlorine levels have generally declined in loon tissue in recent years (Frank et al. 1983).

Heavy metal contaminants may pose the most widespread, irreversible and deadly threat (McIntyre 1988). Methylmercury poisoning has been implicated in lowered productivity (Barr 1986) and winter mortality (Stroud and Lange 1983, Alexander 1985). Mercury is released into the environment during the operation of chlor-alkali and wood pulp plants, and through treatments of agricultural seeds (McIntyre 1988). Lake acidification may accelerate the release of mercury into the water column, hastening its uptake through the aquatic food chain (Barr 1986, McIntyre 1988). In Ontario, Barr (1986) found significantly higher mercury residues and lower successful use of territories in loons on lakes within 160 kilometers downstream of a chlor-alkali plant. High mercury levels in many necropsied loons following a large winter die-off along the Gulf Coast of Florida in 1983 (as many as 7,500 birds) (Alexander 1985) may have contributed to the emaciation and subsequent death of these individuals. In New York, Okoniewiski and Stone (1987) tentatively diagnosed mercury intoxication in three of 29 carcasses examined between 1972-86.

Other heavy metals, such as lead, cadmium and selenium, are actual or potential hazards (McIntyre 1988). Lead poisoning from ingestion of lead fishing sinkers is implicated as a cause of mortality (Locke et al. 1982, Okoniewiski and Stone 1987, Pokras and Chafel, 1992.

Acid precipitation may reduce the quality of nesting lakes. Alvo et al. (1988) monitored reproductive success on 68 small lakes (5.3-75 hectares) near Sudbury, Ontario that varied in pH from 4.0-8.4. Nesting success was higher on lakes with high alkalinity, which was negatively correlated with pH, than on low-alkalinity lakes. Unsuccessful breeding resulted primarily from brood mortalities on acidic lakes and appeared to result from lower prey fish densities. On acidified lakes in New York's Adirondack Park, chicks were fed prey much smaller or larger than those typically preferred (Parker 1988).

Oil spills pose a serious, although localized, threat to habitat. Most spills have occurred on marine wintering areas, and reports of mortality from coastal spills are common (McIntyre 1988). Spills on inland waters, particularly on staging grounds, could be disastrous to migrating loons (McIntyre 1988).

PREDATION: The major predators on nests and chicks include scavengers such as American crows (CORVUS BRACHYRHYNCHOS), common ravens (CORVUS CORAX), herring gulls (LARUS ARGENTATUS) and raccoons (PROCYON LOTOR), all of which have increased due to the proliferation of garbage dumps and other human refuse (McIntyre 1988). Raccoons caused 75-80 percent of nest losses on New Hampshire's two largest lakes in 1977 (Sutcliffe 1980). Other predators include snapping turtles (CHELYDRA SERPENTINA), northern pike (ESOX LUCIUS), muskellunge (ESOX MASQUINONGY), walleye (STIZOSTEDION VITREUM), red fox (VULPES FULVA), mink (MUSTELA VISON), skunk (MEPHITIS MEPHITIS), and occasionally other mammalian carnivores (Olson and Marshall 1952; McIntyre 1975, 1988). Otters (LUTRA CANADENSIS) and bald eagles (HALIAETUS LEUCOCEPHALUS) have been reported as possible predators (Titus and VanDruff 1981, McIntyre 1988). Harassment or disturbance by herring gulls, beavers (CASTOR CANADENSIS) and muskrats may lead to nest abandonment (Titus and VanDruff 1981). Predation on adults appears to be rare (Barklow and Chamberlain 1984, Riedman and Estes 1988).

DISEASES AND PARASITES: Susceptible to epidemics of both type C and type E botulism (McIntyre 1988). Type E botulism has killed up to 3,570 loons on Lake Michigan in a single year (Fay 1966, in McIntyre 1988), probably through ingestion of alewives during migration. Also susceptible to aspergillosis from airborne ASPERGILLUS spp. spores, which destroy the functioning of air sacs, particularly in stressed birds (Okoniewski and Stone 1987, McIntyre 1988). An extensive list of internal parasites has been documented (McIntyre 1988). Carcasses in emaciated condition from a massive die-off along the Gulf coast in 1983 had abnormally high numbers of microphallid trematodes (flukes), as well as tapeworms, spiny-headed worms, renal trematodes and renal coccidia (Stroud and Lange 1983). These parasites are believed to have caused hemorrhagic entritis and contributed to the pronounced emaciation of many dead birds. Loons are afflicted by a host-specific black fly (SIMULIUM EURYADMINICULUM), which may act as a vector and transmit a blood parasite (McIntyre 1975, 1988).

Short-term Trend: Relatively Stable (<=10% change)
Short-term Trend Comments: In the heart of their breeding range, populations appear to be stable or increasing. North American Breeding Bird Survey (BBS) data indicate a non-significant 0.98% annual increase occurred in North America from 2002 to 2012 (http://www.mbr-pwrc.usgs.gov/cgi-bin/atlasa12.pl?00070&1&12). Breeding Bird Surveys in Canada indicate a non-significant positive trend of 0.3 per cent annually, 1990-2000 (Downes et al. 2002) and non-significant positive trend of 0.91 per cent annually, 2002-2012 (Sauer et al. 2014, http://www.mbr-pwrc.usgs.gov/cgi-bin/atlasa12.pl?00070&1&12). See Rimmer (1992) for details on status in northeastern U.S., where breeding populations in the early 1990s were stable or slowly increasing and wintering populations were variable but without a significant upward or downward trend.

Long-term Trend: Decline of <50% to increase of >25%
Long-term Trend Comments: Large declines in breeding populations were recorded in the northeastern U.S. over the past several decades prior to the 1990s (Rimmer 1992). A northward range contraction has been documented within the last 100-150 years, and several states that once supported breeding loons have lost them (McIntyre 1988). See USFWS (1987), Johnsgard (1987), and Hands et al. (1989) for regional status in United States. North American Breeding Bird Survey (BBS) data suggest a non-significant 0.72% annual increase in North America, 1966-2012 (Sauer et al. 2014, http://www.mbr-pwrc.usgs.gov/cgi-bin/atlasa12.pl?00070&1&12 ), although only 31% of the loon's range falls within the BBS survey area (Sauer et al. 2013).

Intrinsic Vulnerability: Moderately vulnerable
Intrinsic Vulnerability Comments: Physiology of the species is not well known and species appears to be vulnerable to environmental toxins, including heavy metals (McIntyre and Barr 1997, Evers et al. 2010).

Environmental Specificity: Narrow to moderate.
Environmental Specificity Comments: None

Other NatureServe Conservation Status Information

Inventory Needs: Further capture and marking that would help answer questions about demography and social interactions (McIntyre and Barr 1997) as well as networking and improvement of monitoring efforts across the range as needed (Evers 2004).

Protection Needs: Coastal wintering areas need protection from the damages of oil spills (Rimmer 1992).

Distribution
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Global Range: (>2,500,000 square km (greater than 1,000,000 square miles)) Nesting occurs in Iceland, Greenland, and across Canada and the northern United States to Alaska, and south to California, Montana, the Great Lakes region, New York, New England, and Nova Scotia (AOU 1998). In winter, this loon occurs mainly 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 the western Palearctic along the Atlantic coast to northwestern Africa (AOU 1998). In North America, this species is most concentrated in winter 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).

U.S. States and Canadian Provinces

Due to latency between updates made in state, provincial or other NatureServe Network databases and when they appear on NatureServe Explorer, for state or provincial information you may wish to contact the data steward in your jurisdiction to obtain the most current data. Please refer to our Distribution Data Sources to find contact information for your jurisdiction.
Color legend for Distribution Map
NOTE: The maps for birds represent the breeding status by state and province. In some jurisdictions, the subnational statuses for common species have not been assessed and the status is shown as not-assessed (SNR). In some jurisdictions, the subnational status refers to the status as a non-breeder; these errors will be corrected in future versions of these maps. A species is not shown in a jurisdiction if it is not known to breed in the jurisdiction or if it occurs only accidentally or casually in the jurisdiction. Thus, the species may occur in a jurisdiction as a seasonal non-breeding resident or as a migratory transient but this will not be indicated on these maps. See other maps on this web site that depict the Western Hemisphere ranges of these species at all seasons of the year.
Endemism: occurs (regularly, as a native taxon) in multiple nations

U.S. & Canada State/Province Distribution
United States AK, AL, AR, AZ, CA, CO, CT, DE, FL, GA, IAextirpated, ID, ILextirpated, INextirpated, KS, KY, LA, MA, MD, ME, MI, MN, MO, MS, MT, NC, ND, NE, NH, NJ, NM, NN, NV, NY, OH, OK, OR, PA, RI, SC, SD, TN, TX, UT, VA, VT, WA, WI, WV, WY
Canada AB, BC, LB, MB, NB, NF, NS, NT, NU, ON, PE, QC, SK, YT

Range Map
Note: Range depicted for New World only. The scale of the maps may cause narrow coastal ranges or ranges on small islands not to appear. Not all vagrant or small disjunct occurrences are depicted. For migratory birds, some individuals occur outside of the passage migrant range depicted. For information on how to obtain shapefiles of species ranges see our Species Mapping pages at www.natureserve.org/conservation-tools/data-maps-tools.

Range Map Compilers: NatureServe, 2002; WILDSPACETM 2002


U.S. Distribution by County Help
State County Name (FIPS Code)
CT Fairfield (09001)*, Hartford (09003), Litchfield (09005), New Haven (09009)*
ID Ada (16001), Adams (16003), Bear Lake (16007), Benewah (16009), Bingham (16011), Blaine (16013), Boise (16015), Bonner (16017), Bonneville (16019), Boundary (16021), Camas (16025), Canyon (16027), Caribou (16029), Cassia (16031), Clearwater (16035), Custer (16037), Elmore (16039), Franklin (16041), Fremont (16043), Gem (16045), Gooding (16047), Idaho (16049), Jefferson (16051), Jerome (16053), Kootenai (16055), Latah (16057), Lemhi (16059), Lewis (16061), Nez Perce (16069), Oneida (16071), Owyhee (16073), Payette (16075), Power (16077), Shoshone (16079), Twin Falls (16083), Valley (16085), Washington (16087)
IN Posey (18129)*
MA Barnstable (25001)*, Franklin (25011), Hampden (25013), Hampshire (25015), Middlesex (25017), Norfolk (25021)*, Plymouth (25023)*, Suffolk (25025)*, Worcester (25027)
MI Alcona (26001), Alger (26003), Allegan (26005)*, Alpena (26007), Antrim (26009), Baraga (26013), Barry (26015), Benzie (26019), Charlevoix (26029), Cheboygan (26031), Chippewa (26033), Clare (26035), Crawford (26039), Delta (26041), Dickinson (26043), Emmet (26047), Gladwin (26051), Gogebic (26053), Grand Traverse (26055), Houghton (26061), Iosco (26069), Iron (26071), Isabella (26073), Kalkaska (26079), Keweenaw (26083), Lake (26085), Leelanau (26089), Luce (26095), Mackinac (26097), Manistee (26101), Marquette (26103), Mason (26105), Mecosta (26107), Missaukee (26113), Montcalm (26117), Montmorency (26119), Newaygo (26123), Oakland (26125)*, Oceana (26127), Ogemaw (26129), Ontonagon (26131), Osceola (26133), Oscoda (26135), Otsego (26137), Presque Isle (26141), Roscommon (26143), Schoolcraft (26153), Wexford (26165)
MT Flathead (30029), Glacier (30035), Lake (30047), Lewis and Clark (30049), Lincoln (30053), Missoula (30063), Powell (30077), Sanders (30089), Teton (30099)
ND Benson (38005), Bottineau (38009), Grand Forks (38035), Nelson (38063)*, Ramsey (38071), Richland (38077)*, Rolette (38079), Stutsman (38093)*
NH Belknap (33001), Carroll (33003), Cheshire (33005), Coos (33007), Grafton (33009), Hillsborough (33011), Merrimack (33013), Rockingham (33015), Strafford (33017), Sullivan (33019)
NV Mineral (32021)*
NY Chautauqua (36013), Clinton (36019), Cortland (36023), Essex (36031), Franklin (36033), Fulton (36035), Hamilton (36041), Herkimer (36043), Jefferson (36045), Lewis (36049), Oneida (36065), Otsego (36077), Saratoga (36091), St. Lawrence (36089), Warren (36113)
OR Clackamas (41005)*, Hood River (41027)*, Lincoln (41041)*, Multnomah (41051)*
SD Day (46037), Marshall (46091)
UT Davis (49011)*, Duchesne (49013), Salt Lake (49035)*, Uintah (49047)*, Utah (49049)*
VT Addison (50001), Bennington (50003), Caledonia (50005), Essex (50009), Grand Isle (50013), Lamoille (50015), Orange (50017), Orleans (50019), Rutland (50021), Washington (50023), Windham (50025), Windsor (50027)
WA Benton (53005)+, Chelan (53007)+, Clallam (53009)+, Cowlitz (53015)+, Douglas (53017)+, Ferry (53019)+, Grant (53025)+, Grays Harbor (53027)+, Island (53029)+, King (53033)+, Kitsap (53035)+, Kittitas (53037)+, Lewis (53041)+, Lincoln (53043)+, Mason (53045)+, Okanogan (53047)+, Pend Oreille (53051)+, Pierce (53053)+, Skagit (53057)+, Skamania (53059)+, Snohomish (53061)+, Stevens (53065)+, Thurston (53067)+, Whatcom (53073)+, Yakima (53077)+
WY Albany (56001), Big Horn (56003), Campbell (56005), Carbon (56007), Converse (56009), Fremont (56013), Goshen (56015), Hot Springs (56017), Johnson (56019), Laramie (56021), Lincoln (56023), Natrona (56025), Park (56029), Platte (56031), Sheridan (56033), Sublette (56035), Sweetwater (56037), Teton (56039), Uinta (56041), Weston (56045)
* Extirpated/possibly extirpated
U.S. Distribution by Watershed Help
Watershed Region Help Watershed Name (Watershed Code)
01 Upper Androscoggin (01040001)+, Saco (01060002)+, Piscataqua-Salmon Falls (01060003)+, Pemigewasset (01070001)+, Merrimack (01070002)+, Contoocook (01070003)+, Nashua (01070004)+, Merrimack (01070006)+, Upper Connecticut (01080101)+, Passumpsic (01080102)+, Waits (01080103)+, Upper Connecticut-Mascoma (01080104)+, Black-Ottauquechee (01080106)+, Middle Connecticut (01080201)+, Miller (01080202)+, Deerfield (01080203)+, Chicopee (01080204)+, Farmington (01080207)+, Cape Cod (01090002)+*, Quinnipiac (01100004)+*, Housatonic (01100005)+*
02 Upper Hudson (02020001)+, Sacandaga (02020002)+, Hudson-Hoosic (02020003)+, Mohawk (02020004)+, Upper Susquehanna (02050101)+
04 Black-Presque Isle (04020101)+, Ontonagon (04020102)+, Keweenaw Peninsula (04020103)+, Sturgeon (04020104)+, Dead-Kelsey (04020105)+, Betsy-Chocolay (04020201)+, Tahquamenon (04020202)+, Waiska (04020203)+, Lake Superior (04020300)+, Brule (04030106)+, Michigamme (04030107)+, Menominee (04030108)+, Cedar-Ford (04030109)+, Escanaba (04030110)+, Tacoosh-Whitefish (04030111)+, Fishdam-Sturgeon (04030112)+, Kalamazoo (04050003)+, Maple (04050005)+, Lower Grand (04050006)+, Thornapple (04050007)+, Pere Marquette-White (04060101)+, Muskegon (04060102)+, Manistee (04060103)+, Betsie-Platte (04060104)+, Boardman-Charlevoix (04060105)+, Manistique (04060106)+, Brevoort-Millecoquins (04060107)+, Lake Michigan (04060200)+, St. Marys (04070001)+, Carp-Pine (04070002)+, Lone Lake-Ocqueoc (04070003)+, Cheboygan (04070004)+, Black (04070005)+, Thunder Bay (04070006)+, Au Sable (04070007)+, Au Gres-Rifle (04080101)+, Tittabawassee (04080201)+, Pine (04080202)+, Lake Huron (04080300)+, Clinton (04090003)+*, Seneca (04140201)+, Black (04150101)+, Chaumont-Perch (04150102)+, Upper St. Lawrence (04150301)+, Oswegatchie (04150302)+, Indian (04150303)+, Grass (04150304)+, Raquette (04150305)+, St. Regis (04150306)+, English-Salmon (04150307)+, Chateaugay-English (04150308)+, Otter Creek (04150402)+, Winooski River (04150403)+, Ausable River (04150404)+, Lamoille River (04150405)+, Saranac River (04150406)+, Lake Champlain (04150408)+, St. Francois River (04150500)+
05 Conewango (05010002)+, Lower Wabash (05120113)+*, Highland-Pigeon (05140202)+*
07 Upper Wisconsin (07070001)+
09 Lower Souris (09010003)+, Willow (09010004)+, Bois De Sioux (09020101)+*, Western Wild Rice (09020105)+*, Devils Lake (09020201)+, Upper Sheyenne (09020202)+*, Middle Sheyenne (09020203)+*, Lower Sheyenne (09020204)+*, Turtle (09020307)+, Forest (09020308)+, Upper Pembina River (09020315)+, St. Marys (09040001)+, Belly (09040002)+
10 Sun (10030104)+, Two Medicine (10030201)+, Teton (10030205)+, Yellowstone Headwaters (10070001)+, Clarks Fork Yellowstone (10070006)+, Upper Wind (10080001)+, Popo Agie (10080003)+, Lower Wind (10080005)+, Upper Bighorn (10080007)+, Nowood (10080008)+, Greybull (10080009)+, Big Horn Lake (10080010)+, Dry (10080011)+, North Fork Shoshone (10080012)+, South Fork Shoshone (10080013)+, Shoshone (10080014)+, Upper Tongue (10090101)+, Crazy Woman (10090205)+, Clear (10090206)+, Beaver (10120107)+, Upper Belle Fourche (10120201)+, James Headwaters (10160001)+*, Upper James (10160003)+, Middle Big Sioux Coteau (10170201)+, Upper North Platte (10180002)+, Pathfinder-Seminoe Reservoirs (10180003)+, Medicine Bow (10180004)+, Little Medicine Bow (10180005)+, Sweetwater (10180006)+, Middle North Platte-Casper (10180007)+, Glendo Reservoir (10180008)+, Middle North Platte-Scotts Bluff (10180009)+, Upper Laramie (10180010)+, Lower Laramie (10180011)+, Horse (10180012)+, Crow (10190009)+
14 Upper Green (14040101)+, New Fork (14040102)+, Upper Green-Slate (14040103)+, Big Sandy (14040104)+, Bitter (14040105)+, Upper Green-Flaming Gorge Reservoir (14040106)+, Blacks Fork (14040107)+, Muddy (14040108)+, Duchesne (14060003)+
16 Upper Bear (16010101)+, Bear Lake (16010201)+, Middle Bear (16010202)+, Lower Bear-Malad (16010204)+, Utah Lake (16020201)+*, Jordan (16020204)+*, Curlew Valley (16020309)+, Walker Lake (16050304)+*
17 Upper Kootenai (17010101)+, Fisher (17010102)+, Yaak (17010103)+, Lower Kootenai (17010104)+, Moyie (17010105)+, Blackfoot (17010203)+, North Fork Flathead (17010206)+, Middle Fork Flathead (17010207)+, Flathead Lake (17010208)+, South Fork Flathead (17010209)+, Stillwater (17010210)+, Swan (17010211)+, Lower Flathead (17010212)+, Lower Clark Fork (17010213)+, Pend Oreille Lake (17010214)+, Priest (17010215)+, Pend Oreille (17010216), Coeur D'alene Lake (17010303)+, St. Joe (17010304)+, Upper Spokane (17010305)+, Lower Spokane (17010307), Franklin D. Roosevelt Lake (17020001), Kettle (17020002), Colville (17020003), Sanpoil (17020004), Chief Joseph (17020005), Okanogan (17020006), Similkameen (17020007), Methow (17020008), Lake Chelan (17020009), Upper Columbia-Entiat (17020010), Wenatchee (17020011), Banks Lake (17020014), Lower Crab (17020015), Upper Columbia-Priest Rapids (17020016), Upper Yakima (17030001), Naches (17030002), Lower Yakima, Washington (17030003), Snake headwaters (17040101)+, Palisades (17040104)+, Salt (17040105)+, Idaho Falls (17040201)+, Upper Henrys (17040202)+, Lower Henrys (17040203)+, Willow (17040205)+, American Falls (17040206)+, Blackfoot (17040207)+, Portneuf (17040208)+, Lake Walcott (17040209)+, Raft (17040210)+, Goose (17040211)+, Upper Snake-Rock (17040212)+, Salmon Falls (17040213)+, Beaver-Camas (17040214)+, Big Lost (17040218)+, Big Wood (17040219)+, Camas (17040220)+, Little Wood (17040221)+*, C. J. Idaho (17050101)+, Middle Snake-Succor (17050103)+, Boise-Mores (17050112)+, South Fork Boise (17050113)+, Lower Boise (17050114)+, South Fork Payette (17050120)+, Payette (17050122)+, North Fork Payette (17050123)+, Weiser (17050124)+, Brownlee Reservoir (17050201)+, Lower Snake-Asotin (17060103)+, Palouse (17060108), Upper Salmon (17060201)+, Middle Salmon-Panther (17060203)+, South Fork Salmon (17060208)+, Lochsa (17060303)+, Clearwater (17060306)+, Lower North Fork Clearwater (17060308)+, Middle Columbia-Hood (17070105)+, Lower Columbia-Sandy (17080001)+*, Upper Cowlitz (17080004), Lower Cowlitz (17080005), Hoh-Quillayute (17100101), Queets-Quinault (17100102), Lower Chehalis (17100104), Siletz-Yaquina (17100204)+*, Strait of Georgia (17110002), Nooksack (17110004), Upper Skagit (17110005), Lower Skagit (17110007), Stillaguamish (17110008), Skykomish (17110009), Snoqualmie (17110010), Lake Washington (17110012), Duwamish (17110013), Puyallup (17110014), Nisqually (17110015), Skokomish (17110017), Hood Canal (17110018), Puget Sound (17110019), Dungeness-Elwha (17110020), Crescent-Hoko (17110021)
+ Natural heritage record(s) exist for this watershed
* Extirpated/possibly extirpated
Ecology & Life History
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Basic Description: A large aquatic bird (loon).
General Description: SUMMARY: A large-bodied, elongate loon with a heavy bill. Breeding adults have a black head and bill and white checkering on the back. Juveniles and winter adults are rather plain gray on the upper side and white below, with an irregular edge to the gray-white junction on the side of the neck. Wingspan around 46 inches (117 cm).

DETAILS: Plumage differences between the sexes are indistinguishable. In alternate (breeding) plumage, the head and neck are velvety black with a slight greenish gloss. Across the throat is a prominent transverse bar of short, vertical white streaks; on either side of the neck is a collar of similar, longer white streaks, not quite meeting in the center of the throat or the back of the neck. The bill is black, and the iris is brownish ruby. The upperparts are black with a greenish gloss, heavily spotted with white, each feather (except the unmarked upper tail coverts) with a pair of white, squarish subterminal spots, smallest on the upper mantle, back and rump, and largest on the scapulars. The underparts are mainly white, the sides of the breast are streaked black and white, and the flanks are black with small white spots. The tail is short, with 16-20 feathers, and entirely black. The wings are narrow and pointed, about 35 cm long (unflattened), with 11 primaries and 22-23 secondaries. The remiges are blackish with dark shafts, and the tips of the inner secondaries have single or paired white spots. The coverts are similar to the upperparts but have more circular subterminal spots. The wing lining is mostly white. The legs are black on the outer side paling to grayish or white inside; the webs of the feet are mostly white above, and black with white centers below (Palmer 1962, Jackson 1976, Johnsgard 1987, McIntyre 1988).

Although some overlap exists between the sexes, within pairs, males are consistently larger than females (Barr 1973, McIntyre 1988). Adults measure about 1 m in length outstretched (Palmer 1962, McIntyre 1988). Weight varies geographically and within populations, with adults ranging from 2.7 kg to more than 6.3 kg (McIntyre 1988). Sexual dimorphism is most pronounced in bill length and depth (McIntyre 1975, Storer 1988). Some structures of the digestive tract are larger in males, suggesting possible food partitioning by pair members (Barr 1973).

The definitive alternate plumage is acquired by a complete molt between January and March, which renders birds flightless for nearly a month (Woolfenden 1972, McIntyre 1988). This plumage is not acquired until the third or fourth summer (McIntyre 1986).

The basic (winter) plumage is acquired by a partial molt of contour feathers beginning in late summer and lasting through fall (although earlier in unsuccessful breeders and immatures). In this plumage the forehead, crown and back are grayish-brown, and the chin, throat and foreneck are white. The bill is brownish-gray to pale bluish-gray or horn colored. The iris is brown. The upperparts are brownish-gray, the feathers margined with paler gray, with a few black and white feathers occasionally retained in adults. The underparts are mainly white, with a brownish, streaked appearance on the sides of the breast and flanks. The tail is dark brown, tipped with white (Bent 1919; Johnsgard 1987; McIntyre 1986, 1988).

The juvenal plumage begins to emerge at about one month. This plumage is similar to the adult basic plumage, although the upperparts have paler and more conspicuous feather margins than those of adults, and the throat and sides of the neck are more finely streaked with brown. Flight feather growth is completed at 12-13 weeks of age, and this entire plumage is worn until the following summer when a complete molt produces another, more adult- like basic plumage (Palmer 1962, McIntyre 1988).

Newly-hatched chicks undergo two successive changes of downy plumage. The first down is blackish, paler on the throat, upper breast and flanks, and white on the lower breast and belly. This is replaced at 10-14 days of age by the second downy plumage of primarily brownish-gray feathers, which are replaced by the juvenal contour feathers at four weeks (Palmer 1962, McIntyre 1988).

NESTS: Nests are nearly always built at the water's edge. Substrates range from masses of aquatic and terrestrial vegetation, to moss, to bare soil, sand or rock, to depressions in old muskrat (ONDATRA ZIBETHICUS) houses (McIntyre 1988). Nests are typically large, bulky structures composed of vegetation, if available, but may consist simply of scrapes in the bare soil or duff, or may be placed directly on rocky substrate (Bent 1919, McIntyre 1988). Some are built on sedge or ericaceous bog mats, and occasionally partially rotted, semi-submerged logs are used (McIntyre 1988). Nest materials often include clumps of partially decayed aquatic vegetation, roots and rhizomes (McIntyre 1975, 1988). Nest diameters average 56-66 centimeters outside, 24.5-33 centimeters inside, and 3-7.6 centimeters deep (Olson and Marshall 1952, McIntyre 1975, Sutcliffe 1980).

EGGS: Subelliptical to ovoid in shape and vary from deep-olive to light-brown in color, most being deep-olive brown with irregular dark brown or black spots. Dimensions average 86.5-91.5 mm by 54-57 mm, and weights average 140-160 g.

VOCALIZATIONS: See Barklow (1979), Klein (1985), McIntyre (1988), Miller (1988), Palmer (1962), Rummel and Goetzinger (1975), Sjolander and Agren (1972) for descriptions of vocalizations.

Diagnostic Characteristics: See Stallcup (1994) for information on identification of North American loons.
Reproduction Comments: BRIEF SUMMARY: Egg-laying begins one to several weeks after spring arrival, usually during mid-May in the south, and well into June farther north. Replacement clutches may be initiated as late as early July. Incubation lasts around 4 weeks. Chicks leave the nest within 24 hours of hatching and are soon moved to nursery areas. Chicks may be carried on their parents' backs until they reach three weeks of age. Most juveniles are capable of flight at 11-12 weeks, and some leave their small, natal lakes or parental territories shortly afterward.

ARRIVAL AND TERRITORY ESTABLISHMENT: Timing of spring arrival is correlated with latitude and dictated primarily by ice-out phenology (McIntyre 1988). In southern portions of the breeding range, pairs may reoccupy territories in March, while at northern latitudes arrival may be delayed until mid or late May (McIntyre 1988). In Minnesota, an average of eight days elapsed between ice break-up and loon arrival in an early ice-out year, five days in an average year, and three days in a late year (McIntyre 1975). 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 chicks hatch and shrinking for failed pairs (McIntyre 1988).

COURTSHIP: It is believed that pairs remate each spring and that courtship serves primarily to renew the pair bond (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).

NESTING PERIOD: 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, usually during mid-May in the south, and well into June farther north (Palmer 1962, McIntyre 1975). Eggs are typically laid at two-day intervals (McIntyre 1975). Replacement clutches following failures of first nests are common (McIntyre 1975, 1988). Renests have been reported to occur within five days of a nest loss (Olson and Marshall 1952), but intervals of 10-14 days appear to be most common (Olson and Marshall 1952, McIntyre 1975, Sutcliffe 1980). Up to three laying cycles have been recorded in a season (Olson and Marshall 1952, McIntyre 1975). Nests lost early in the season are more likely to be replaced than those lost later (McIntyre 1988). Replacement clutches have been initiated as late as early July in Vermont (Kaveney and Rimmer 1989). If waters rise during incubation, loons continue adding to the nest's height to prevent flooding (McIntyre 1988). Replacement nests tend to have smaller outside dimensions (McIntyre 1975). Nest bowls are often reused in subsequent years, and occasionally within years for replacement clutches (Strong et al. 1987).

CLUTCH SIZE AND INCUBATION: Most clutches contain two eggs, and most one-egg clutches result from loss of the first egg (McIntyre 1975, Titus and VanDruff 1981). Three-egg clutches are very rare (Bent 1919, McIntyre 1988), and only two four-egg clutches have been reported (Nelson 1983, Zicus et al. 1983). Second eggs are smaller than first eggs, and eggs in replacement clutches are smaller than those in original clutches (McIntyre 1988). Both pair members incubate, beginning with the laying of the first egg, for an average period of 28-29 days, ranging from 26-31 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).

CHICK REARING: Chicks leave the nest within 24 hours of hatching and are soon moved to nursery areas (McIntyre 1988). In Saskatchewan, nurseries were located an average of 500 m from nest sites and occupied about 15 percent of territory size (McIntyre 1983). Both adults tend the young by feeding, carrying and defending them for several weeks. Chicks are carried on their parents' backs until they reach three weeks of age (McIntyre 1975). Although 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), they are fed largely by their parents until eight weeks of age (McIntyre 1988). Adults aggressively defend chicks underwater and on the surface (McIntyre 1988). Most juveniles are capable of flight at 11-12 weeks (Barr 1973, McIntyre 1975), and some leave their small, natal lakes or parental territories shortly afterwards (McIntyre 1975).

NESTING SUCCESS: Breeding success varies considerably among populations. Most failures occur during incubation, from factors such as predation, flooding or stranding due to water level fluctuations, and human intrusion (Olson and Marshall 1952, McIntyre 1975, Wood 1979, Titus and VanDruff 1981, Rimmer and Kaveney 1988). In Ontario, lack of attempted breeding was associated with small, brown, low-alkalinity lakes; successful breeding associated with large, clear, high-alkalinity lakes; unsuccessful breeding resulted primarily from brood mortalities on acidic lakes, most likely due to shotage of suitable food for young (Alvo et al. 1988).

Chick survival is relatively high, especially after chicks reach two to three weeks of age (McIntyre 1988). However, Alvo et al. (1988) recently found higher mortality of older chicks on highly acidified lakes in Ontario, due to presumed starvation from an inadequate food base. Fledging success (percent of hatched chicks fledged) from a sample of 1,500 pairs across the breeding range averaged 80 percent (range = 67-94 percent ) (McIntyre 1988). Productivity (number of fledglings per pair) of this sample averaged 0.60 and varied widely between 0.22 for nine pairs in Minnesota (McIntyre 1975) and 0.97 for 132 pairs in New York (Parker and Miller 1988).

SITE FIDELITY: Appear to be faithful to breeding territories. Banded adults have been recaptured on the same breeding territory in subsequent years (McIntyre 1974, Yonge 1981, Eberhardt 1984). 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.

Ecology Comments: Hectares of water area per territorial pair: 503 (New Hampshire); 44, 73 (Minnesota); 39 (Saskatchewan); 351 (New York) (Johnsgard 1987). Lakes smaller than 80 ha generally support only one breeding pair. Typically, territory size is larger on large lakes than on small lakes. Generally, loss of eggs to predators is not a primary cause of breeding failure (Johnsgard 1987). Wintering birds may defend feeding territories during the day, gather into rafts at night.

Ecology of wintering 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).

Non-Migrant: N
Locally Migrant: N
Long Distance Migrant: Y
Mobility and Migration Comments: Northward migration occurs mainly in April-May, southward return begins late August-early September in the interior, continues until freeze-up (Johnsgard 1987). Migrants arrive in the far north (northern Alaska) in late May or early June. In the southern part of the nesting range, breeding territories may be occupied as early as March.

Migrants move singly or in small groups, mostly by day. They move offshore, along continental shelf, inshore, and inland; loons breeding at Great Lakes migrate eastward to Atlantic coast and then southward to wintering areas along the southeastern U.S. coast. Typically they congregate on staging areas on large lakes following the breeding season and during fall migration.

Atlantic pathways are offshore, along the continental shelf from Nova Scotia to the Carolinas, and farther inshore, following the coast across Cape Cod (Powers and Cherry 1983). Band recovery data document inland pathways along a broad southeast/northwest front between the Atlantic Coast and central Canada, funneling primarily through Lake Michigan and Georgian Bay on Lake Huron (McIntyre 1988). Some birds migrate along a north/south line through the central U.S. to and from the Gulf of Mexico (McIntyre 1988). Loons breeding in Alaska and western Canada appear to move along the western edge of the Rocky Mountains en route to and from the Pacific Coast (McIntyre 1988).

Both adults and juveniles typically congregate on staging areas on large lakes following the breeding season (e.g., Bull 1974, McIntyre and Barr 1983, McIntyre 1988). Large concentrations also build on the Great Lakes and other inland lakes during the fall migration. Loons may linger on freshwater lakes until freeze-up before moving to maritime wintering sites (McIntyre 1988). The spring migration is direct and closely follows the northward retreat of ice (McIntyre 1988). Loons are diurnal migrants, and most flights, whether coastal or overland, appear to be initiated in the early morning (Williams 1973, Kerlinger 1982, Powers and Cherry 1983). The movements of juveniles during their three to four years as nonbreeders are not well understood. Most appear to remain on the coast, but some may move hundreds of miles northward, possibly tracking fish movements (McIntyre 1988).

Marine Habitat(s): Near shore
Estuarine Habitat(s): Bay/sound, Lagoon, River mouth/tidal river
Riverine Habitat(s): BIG RIVER
Lacustrine Habitat(s): Deep water, Shallow water
Palustrine Habitat(s): Bog/fen, HERBACEOUS WETLAND, Riparian
Habitat Comments: Breeding habitat includes usually clear lakes (McIntyre 1988) containing both shallow and deep water areas (McIntyre 1975, 1988; Strong 1985). In studies comparing lakes with and without loons, higher turbidity was suggested as a factor influencing lack of occupancy (Barr 1973, McIntyre 1988). Nest sites are on small islands(Olson and Marshall 1952, Vermeer 1973, McIntyre 1975, Titus and VanDruff 1981, Strong 1985), quiet backwaters (Strong 1985), or mainland shores. Loons have been found nesting in marshy portions of lakes in water depths no greater than 0.5 m (Alvo 1981). Optimal nest sites, as measured by degree of success, include overhead cover to conceal eggs from predators, protection from wind and waves, good visibility by incubating adults, and a steep slope adjacent to the nest for adequate underwater approaches and exits (McIntyre 1975, 1983, 1988). Brood-rearing areas are typically located in shallow coves of fairly uniform depth, sheltered from prevailing winds and wave action, and are independent of nest site location (McIntyre 1983, Strong 1985). Adults tending chicks prefer shallow water areas (< 2 m) close to land (< 150 m) (Strong 1985, Strong and Bissonette 1989). Deepwater areas (> 4 m) distant from land (> 250 m) are avoided by feeding adults and adults tending chicks, but are often used for social interactions (Strong 1985). Breeding adults usually feed outside of nursery areas (Strong 1985), occasionally outside of their territories (McIntyre 1983), and may visit nearby lakes for feeding (Miller and Dring 1988).

In winter and during migration, common loons use inland lakes and rivers and marine and estuarine coastal waters. Most nonbreeding subadults apparently remain in coastal areas during breeding season. Winter primarily in coastal marine habitats, including bays, coves, channels, inlets and other shallow areas (Bent 1919, McIntyre 1988, Palmer 1962). Some individuals overwinter on inland lakes and rivers, although this appears to be largely weather influenced (McIntyre 1988). While shallow, inshore waters appear to be utilized more frequently than deeper, offshore waters (McIntyre 1978, Daub 1989), some use continental shelf waters up to 100 m in depth and 100 km from land (Haney 1990). In the southeastern U.S. (between 29 degrees and 35 degrees North latitude), wintering loons were most common in waters up to 19 m deep but were rare or absent in highly turbid waters five to 15 km from shore. Loon distribution shifted farther offshore during midwinter to avoid increases in these turbid water areas (Haney 1990). Feeding typically occurs in water depths less than five meters, while maintenance activities (e.g., preening and drifting) take place in deeper water (McIntyre 1978, Daub 1989).

Adult Food Habits: Piscivore
Immature Food Habits: Piscivore
Food Comments: Common loons dive from the water's surface, feed mainly on fishes; also amphibians and various invertebrates (Terres 1980). If nesting on a small lake, they may use an adjacent lake for supplementary foraging (Johnsgard 1987). In Ontario, loons attempting to raise young on a fishless acidic lake fed chick benthic algae and possibly benthic invertebrates but flew to other lakes to feed themselves (Alvo et al. 1988). Feeding occurs usually in waters less than 5 meters deep.

These loons are primarily piscivorous but are opportunistic and will eat any suitable prey they can readily see and capture (McIntyre 1988). 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, loons have been reported feeding on molluscs, insects, amphipods and amphibians (Munro 1945, Parker 1985). Young 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.

Adult Phenology: Circadian
Immature Phenology: Circadian
Length: 81 centimeters
Weight: 4134 grams
Economic Attributes Not yet assessed
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Management Summary
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Stewardship Overview: Nest on islands or backwater areas on lakes with adequate fish prey. Pairs typically raise one or two chicks, but failure is common and compensated sometimes by renesting. On the northern breeding grounds in Canada, populations appear to be stable or increasing. However, at the southern edge of their range in the Northeast, breeding loons have gradually drawn northward in the past century. Many types of disturbances threaten loons at their breeding sites, including lakeshore development, human recreational disturbance, predation, fluctuating water levels at nest sites, entanglement in fishing gear, environmental pollutants, and loss of prey due to acidic rain. Identification, monitoring and protection of nest sites in areas of human use are essential to the continued nesting success. Wintering areas along the Pacific and Atlantic coasts also require protection from the damages of oil spills. More information is needed about wintering areas, distribution, and numbers (Rimmer 1992).
Restoration Potential: The ability to habituate to moderate levels of lakeshore and recreational use indicates that populations may continue to survive if suitable breeding, staging, stopover and wintering habitats are available. Loons are currently increasing in Vermont, New Hampshire and Massachusetts, and populations appear to be stable in New York and Maine. Just as human-induced habitat changes and recreational pressures probably caused the widespread declines noted prior to the 1970s, integrated management programs have contributed to the recovery in much of their northeastern U.S. breeding range. The potential for continued recovery is favorable (Rimmer 1992).
Preserve Selection & Design Considerations: Because of vulnerability to habitat loss or degradation, lakes that support breeding loons or serve as important migratory stopover sites need protection (Rimmer 1992). Identification and protection of known nesting areas is an important strategy because loons exhibit strong year-to-year fidelity to old nest sites (Strong and Bissonette 1985). When possible, two or three alternate sites with characteristics of preferred nesting areas (e.g., islands, deadwaters, marshes, protected coves) should be protected on each breeding lake. Small islands (< 5 ha) and deadwaters should receive complete protection from development. Undeveloped buffer zones of at least 150 m should be left on either side of mainland nest sites or deadwater entrances (Strong and Bissonette 1985). Shoreline areas adjacent to known traditional nursery areas should also be protected, with minimum undeveloped buffer zones of 150 m from both ends of the nursery (Strong and Bissonette 1985). Purchase of known nesting areas or suitable lakeshore breeding habitat by state or private conservation organizations, or acquisition of options to protect such lands from development (e.g., easements and zoning ordinances), may preserve loon nesting habitat (McPeek and Evers 1989).
Management Requirements: Protection techniques have focused on the breeding season and have involved primarily management of both habitat and people (Rimmer 1992). Loons have responded successfully to management by private conservation groups and state agencies. Most of the organizations that conduct statewide monitoring programs also coordinate management efforts.

CONTROL OF WATER LEVELS: Nest losses caused by flooding can be reduced by maintaining constant water levels during the peak nesting period (Fair 1979, Wood 1979), usually mid- May to mid-July in New York and New England. Rises in water level are more detrimental than drawdowns, and small drawdowns may be acceptable if distances between nests and the water's edge are not greatly increased (Strong and Bissonette 1985). In areas of recent flooding, all flooded timber should be cut and removed to minimize the amount of driftwood on shorelines (Strong and Bissonette 1985).

NESTING PLATFORMS: Artificial nesting platforms may improve nesting success on lakes that lack natural islands and have poor shoreline nesting habitat, fluctuating water levels, or a history of low productivity. Platforms rise and fall with water levels and can counteract extreme fluctuations on lakes where loons are not considered in water management plans (Wood 1979). Platforms have increased nesting success in Minnesota (McIntyre and Mathisen 1977), New Hampshire (Sutcliffe 1979, Fair 1989), Vermont (Rimmer and Kaveney 1988), and Massachusetts (Lyons 1987). Platforms alone are unlikely to induce nesting on unoccupied lakes or territories (McIntyre and Mathisen 1977, Sutcliffe 1979) and should not be used as mitigation to development or water level manipulation (Strong and Bissonette 1985). Plans for the construction of loon platforms are available from the North American Loon Fund.

PREDATOR MANAGEMENT: Predators can be the major cause of breeding failure in some areas. Removal of raccoons by hunting or trapping has met with some success in New Hampshire, but is labor-intensive and expensive (Wood 1979), and probably of only temporary benefit. Nesting platforms may reduce mammalian predation, which often increases after water levels drop (Fair 1979, Sutcliffe 1979). Improved methods of garbage disposal could reduce nest predation by crows, gulls, and raccoons, which are often attracted to human refuse (Hands et al. 1989).

FISH TRAPS: Mortality on the Great Lakes from commercial fishing operations could be reduced by using traps that open at the top to allow loons to escape and also by more frequently checking traps for captured loons. A cooperative program must be developed between commercial fishers and government agencies (McIntyre 1986).

PUBLIC EDUCATION: Human disturbance during the nesting and chick-rearing periods can be controlled in many ways. Activities such as boating, fishing, swimming, camping and picnicking should be prohibited near nest sites and in nursery areas. Closures of nest and brood-rearing sites through posting are recommended only in situations of heavy boat traffic where the closure can be reinforced through steady monitoring by law enforcement officials or volunteers (Wood 1979; J. Fair, pers. comm.). Interpretive signs posted at boat ramps, beaches, campgrounds and other public access points should inform recreationists about the natural history and conservation needs of loons. The number of visitors to wilderness areas could be restricted and specific travel routes established. Visitors could be required to attend an educational program before entering a recreational area with breeding loons (Titus and VanDruff 1981). No camping should be allowed on small islands, and other uses should be discouraged (Titus and VanDruff 1981) or, if necessary, prohibited. Boat engine horsepower limitations or speed limits should be established on smaller breeding lakes or in designated areas of large lakes.

Informational brochures, posters, press releases and other educational paraphernalia should be produced and distributed (Strong and Bissonette 1985, McIntyre 1986). Educational programs, including filmstrips and slide lectures, should be presented to schools, lake associations and other groups. Personal contacts with lakeshore residents should be established and maintained. Monitoring by volunteers may be especially important on lakes with relatively low human use where the presence of law enforcement officials may not be feasible. Involvement of volunteers in lake patrols and population surveys may stimulate public interest and reduce levels of human disturbance.

Monitoring Requirements: It is important to continue monitoring population trends and productivity in all states where loons nest (Rimmer 1992). Censusing of adult populations can begin shortly after arrival on the breeding grounds, although such counts may also include northbound transients. Populations of breeding and nonbreeding adults are most accurately estimated by repeated, standardized surveys after territory establishment in mid-May. In states such as Vermont, New Hampshire and Massachusetts, it may be possible to census all or nearly all suitable breeding habitat and to accurately determine population levels and productivity totals. In the larger states of New York and Maine, a specified sample of lakes should be surveyed annually, or every few years, to document population trends. Strong and Bissonette (1985) suggested that aerial counts of loons on 50-100 randomly selected lakes in Maine should be conducted every three to five years. To monitor breeding status and productivity, they recommended the establishment of a more regularly surveyed network of lakes. In New York, presence, reproductive success, and density were compared on a subsample of 384 "core lakes" from a larger sample during 1977-79 and 1984-85 surveys (Parker et al. 1986, Parker and Miller 1988)

Breeding can be verified by the presence of a recently used nest or of flightless young. Lake and island perimeters, bog mats, and floating vegetation can be carefully checked to find nests. Precautions should be taken not to flush incubating birds, since it is not necessary to view nest contents to confirm nesting. Nest searches should not be conducted during cold or wet weather. Follow-up visits can be made to determine breeding chronology and outcome. Chicks should not be considered fledged until at least one month old (McIntyre 1988).

Volunteer assistance can often be enlisted on a regular basis for surveys and monitoring of known breeding pairs, especially in more developed areas. Coordinated censuses, in which volunteer observers are assigned a lake or portion thereof to monitor during a specified time period on a specified date, provide an additional means to estimate populations. These simultaneous counts provide an index of lake occupancy and productivity and can be used to refine statewide population totals. They are typically conducted in midsummer, just after the peak period of chick hatching.

Christmas Bird Counts should be continued to monitor trends in distribution and abundance in early winter. These data should ideally be complemented by those from more standardized, repeated surveys at specific concentration points throughout the winter (e.g., Lee and Arbuckle 1988). A coastwide winter loon watch would provide important information on wintering patterns (McIntyre 1986). Data on wintering loons could also be collected during aerial midwinter waterfowl surveys conducted by the U.S. Fish and Wildlife Service (D. Pence, pers. comm.).

Management Research Needs: The North American Loon Fund annually provides small grants to researchers studying a diversity of topics on loon biology, behavior and conservation. A list of current and past projects that have received funding, as well as grant application guidelines, can be obtained by contacting the fund.

Wintering Distribution and Ecology. Detailed information on the precise wintering distribution and abundance is lacking. Little is known about the distribution of discrete breeding populations, the ecological requirements and social structure of wintering loons, the relationship between adults and juveniles, causes and rates of mortality, the impacts of environmental contaminants or oil spills, the effects of weather, the impacts of commercial fishing, the site preferences of individual loons or different age and sex classes, and the mobility of loons during winter. In addition to research addressing these topics, monitoring programs such as a coordinated coastal winter watch or midwinter aerial survey should be initiated.

More information is needed on migration routes and staging areas in spring and fall. Little is known about the habitat and feeding requirement during migration, the residence times of individuals on staging areas, the effects of weather or human disturbance on migrating loons, and age and sex differences in the timing, route selection and ecology of migrant loons. Coordinated migration watches should be conducted at strategic coastal and inland sites.

Studies are needed on the life history of juveniles between fledging and their return to northern lakes. Little is known about their ecological needs and habitat use, diet, migration routes, wintering distribution, movements during their two or more years as nonbreeders, causes and rates of mortality, social relationships and behavior, age at which the definitive alternate plumage is acquired, age at first breeding, and degree of philopatry to natal lakes.

Research is needed on the energetic requirements of adults and young, recruitment patterns of young and nonbreeders into breeding populations, effects of intraspecific competition on breeding status and success, site fidelity and territory turnover patterns, duration of pair bonds, and patterns of lake colonization or recolonization.

Levels of chemical contaminants in adults and eggs should be monitored on a regular basis. Studies should attempt to determine the biological consequences of chemical and heavy metal toxification so that discharge practices can be modified if necessary. Monitoring should be continued on the effects of lake acidification on breeding loons.

Studies should be undertaken to quantify and assess the impacts of entrapment in commercial fishing nets and traps.

Research is needed on the causes of type E botulism and how outbreaks can be prevented or minimized.

The answers to many important questions on loon movements, behavioral ecology and demography require the banding and marking of individual birds. The development of improved capture methods is essential. Protocols must be designed for individually marking discrete populations on both the breeding and wintering grounds. Feasibility studies should be initiated to design and test radio transmitters that can be used on loons (Rimmer 1992).

Biological Research Needs: Research on the physiology and metabolic routes of the Common Loon is needed in light of its apparent suseptability to environmental toxins; also expanded public education would further accomplishments already seen from intensive education programs that has resulted in reversal of population declines (McIntyre and Barr 1997, Evers et al. 2010).
Population/Occurrence Delineation
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Group Name: Loons

Use Class: Breeding
Subtype(s): Foraging Area, Nest Site
Minimum Criteria for an Occurrence: Evidence of historical breeding , or current and likely recurring breeding, at a given location, minimally a reliable observation of one or more breeding pairs in appropriate habitat. Be cautious about creating EOs for observations that may represent single breeding events outside the normal breeding distribution.
Mapping Guidance: Map multiple nesting territories on the same lake by enclosing them in a single polygon, using the shoreline of the lake as the boundary. The occurrence should include the parts of the lake used for courtship, nesting, brood rearing and feeding. Map nesting territories or foraging areas on multiple lakes or other water bodies with multiple polygons using the shorelines as the polygon boundaries. For one pair on a lake of less than 80 hectares, the boundary will usually be the entire lake shore.
Separation Barriers: None.
Separation Distance for Unsuitable Habitat: 10 km
Separation Distance for Suitable Habitat: 10 km
Separation Justification: Loons are large birds that often fly between lakes or, in many cases, to marine environments to feed. Red-throated Loons fly up to 14-20 kilometers from the nest to feed (summarized by Barr et al. 2000). Thus a large separation distance is appropriate; the distance is a compromise between the high mobility of loons and the need for occurrences of practical size for conservation purposes. Occurrences do not necessarily reflect discrete populations or metapopulations.

Inferred Minimum Extent of Habitat Use (when actual extent is unknown): 1 km
Inferred Minimum Extent Justification: Home range sizes generally not available. This distance based conservatively on a breeding territory size of 80 hectares; i.e. does not include foraging lakes or salt water separate from nesting lake.
Date: 28Oct2004
Author: Cannings, S., and G. Hammerson

Use Class: Nonbreeding
Minimum Criteria for an Occurrence: Evidence of recurring presence of wintering flocks (including historical); and potential recurring presence at a given location, minimally reliable observations of 25 birds in appropriate habitat for at least 20 days annually. Be cautious about creating EOs for observations that may represent single events.
Separation Barriers: None.
Separation Distance for Unsuitable Habitat: 10 km
Separation Distance for Suitable Habitat: 10 km
Separation Justification: Separation distance somewhat arbitrary. Ecology of wintering loons not well known. Apparently have territories of 4-8 hectares under some circumstances, but raft together at night (McIntyre 1978); in other studies gathered in feeding assemblages (Daub 1989).
Date: 11Apr2001
Author: Cannings, S.
Population/Occurrence Viability
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U.S. Invasive Species Impact Rank (I-Rank) Not yet assessed
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Authors/Contributors
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NatureServe Conservation Status Factors Edition Date: 30Jun2014
NatureServe Conservation Status Factors Author: Hammerson, G. (2010-01-29); partially modified by C. C. NeSmith (2014).
Management Information Edition Date: 01Jun1992
Management Information Edition Author: RIMMER, C.C.; REVISIONS BY M. KOENEN AND D.W. MEHLMAN
Management Information Acknowledgments: Parts of this abstract were originally published by the U.S. Fish and Wildlife Service in Schneider and Pence (1992). Funding for the preparation of the original document was made possible by the U.S. Fish and Wildlife Service, Newton Corner, Massachusetts. State-specific information regarding distribution and population trends was received from the following individuals: L. Bevier, B. Blodget, J. Fair, J. W. McIntyre, D. Monette, B. M. Poirier, and S. Stockwell. Special thanks are extended to J. W. McIntyre and K. E. Parker whose critical reviews of an earlier draft greatly improved this report.
Element Ecology & Life History Edition Date: 29Jan2010
Element Ecology & Life History Author(s): Hammerson, G.

Zoological data developed by NatureServe and its network of natural heritage programs (see Local Programs) and other contributors and cooperators (see Sources).

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