Demography and Populations

Classic example of a K-selected species; long-lived and relatively low lifetime reproductive performance. Life history strategy indicates evolution in stable habitats and populations that approximate carrying capacity. Concentrated capture, color-marking, and re-observation efforts over the past 20 years by BioDiversity Research Institute (Evers et al. 1998, 2000, 2008, Evers 2001) and collaborators (Piper et al. 1997b, 2006, Meyer et al. 1998) provide strong foundation for quantifying demographic features previously unknown. Spatially-explicit differences in demographic parameters likely exist. New England and upper Great Lakes breeding populations most closely studied.

Measures Of Breeding Activity

Age Of First Breeding; Intervals Between Breeding

Immatures regularly return to breeding areas at age three, even though they molt into their alternate plumage by age two (BRI unpubl. data, W. Piper pers. com., D. Long pers. com.). Annual survivorship for the first three years averages 41% (BRI unpubl. data, M. Mitro, pers. com.). Average age at first-breeding for Common Loons is 6 years (range 4 - 11 yr; Evers et al. 2000, W. Piper, pers. com.). Based on 2,128 adult uniquely banded, color-marked adults known to remain on breeding territory for at least 17 years (DCE), adults often usurped from breeding territory and may take 1 to 3 years or more to reoccupy a breeding territory (BRI unpubl. data).

Clutch

Usually 2 eggs. All 3 or 4 egg clutches reported (JWM and JFB, Nelson 1983, Zicus et al. 1983) are likely from multiple females (see Breeding: eggs, above). Genetic confirmation of >2 eggs in a clutch laid by the same female is still needed. Third egg may be from a second female or represents a second nesting attempt overlaying the first nesting attempt. Clutch replaced if initial clutch lost early in breeding season, but not if chicks lost; too late for repeat breeding at that stage (JFB, JWM). Second nesting attempt contains one egg 53% of the time (LPC unpubl. data). See also Breeding.

Annual And Lifetime Reproductive Success

Annual. Rate of reproductive success has been repeatedly measured across much of range, particularly in the southern periphery (see Appendix 2). Estimated overall productivity is best determined by counting the number of territorial pairs and fledged young within a target area (or number of chicks fledged per number of territorial pairs). Because number of young that actually fledge (independence/first flight) is difficult to substantiate, most monitoring programs use a surrogate of “chicks greater than 6 weeks of age” (or nearly in full basic plumage). Chick mortality after 6 weeks is minimal and serves as a suitable predictor of fledging rate. Multi-year studies based on standardized methodologies have estimated overall productivity for 17 study areas (representing 8 states and 5 provinces) (Appendix 2). The average overall productivity from standardized studies across North America is 0.53 fledged young per territorial pair with a range of 0.28 to 0.96.

Many studies do not collect information for established territorial pairs and loon chicks greater than 6 weeks of age, or had other limitations; such studies are common in Sutcliffe 1979, Strong 1988a, Morse et al. 1993, McIntyre and Evers 2000.

Standardized long-term, statewide monitoring programs, like those in New Hampshire and Vermont, provide invaluable datasets for understanding long-lived species like loons. In New Hampshire, the Loon Preservation Committee (LPC) has collected high-resolution productivity data for 33 years. The Vermont Center for Ecostudies (VCE) has similar data for Vermont for a 26-year period.

In New Hampshire, the long-term LPC data show an overall mean productivity rate of 0.52 +/- 0.09 fledged young per year and a range of 0.30 to 0.73, or 143% difference between the lowest and highest (Taylor and Vogel 2003). The VCE average overall productivity is 0.72 +/- 0.15 with a range of 0.35 to 0.98 (Hanson et al. 2002) – the Vermont breeding population is exhibiting a rapid increase. The long-term variability within these databases is approximately 20%; outlier years with extremely low or high productivity only occur once every decade. Given this high inter-annual variability, single year overall productivity numbers have limited value. Based on LPC data, six or more consecutive years of monitoring data are needed to confidently predict average productivity rates.

The agreement in average overall productivity rates over space and time, as reflected in the North American mean and the long-term dataset in New Hampshire, together with the results from recently developed models (Mitro et al. 2008, Grear et al. 2009), indicate that approximately 0.48 fledged young per territorial pair is needed to support sustainable breeding populations (DCE).

Lifetime. A population model for New England and the Great Lakes, based on 0.48 young fledged per territory per year, indicates a breeding loon with average productivity for 24 years (based on first age breeding of 6 years and an estimated lifespan of 30 years) will produce approximately 12 young. Of these young, approximately 41% will return to their natal breeding area at age three (Piper, pers. com.) and even fewer, based on 8% annual mortality, will survive to breeding age. Therefore, the calculated lifetime reproductive success (LRP) is 12 fledged young of which three or four will likely survive to breeding age.

Number Of Broods Normally Reared Per Season

One.

Proportion Of Total Females That Rear At Least One Brood To Nest-Leaving Or Independence

Based on long-term monitoring of territorial pairs in New Hampshire (n = 5,405 territorial pair years), 43% of females produce at least one hatchling and 38% of females produce at least one fledgling (LPC, unpubl. data).

Life Span And Survivorship

An analysis of nearly 1500 re-observations of New England and Great Lakes breeding loons indicate an adult average annual survivorship rate of 92% (Mitro et al. 2008; BRI unpubl. data). No statistical difference between male and female rate of annual survival found. Since this estimate reflects the average survival of unknown aged adults, it provides the average for a cohort of breeding adults that have been followed for 1-14 yr (Evers 2001), and does not necessarily reflect the probability of survival for the entire life of an individual loon.

Longest recorded lifespan for individuals banded as adults (based on potential earliest breeding at 4 years of age) is 21 yr for two New Hampshire females and 23 yr for a Michigan male (banded as a chick) (DCE).

Disease And Body Parasites

Diseases

Of 222 dead loons examined between 1976 and 1991, 18% were thought to have died of disease; of this diseased proportion, 38% of the deaths were attributed to botulism, 33% to aspergillosis (Franson and Cliplef 1993). Die-offs on the Great Lakes, especially Lake Michigan, by avian botulism Types E and C are erratic but extensive (e.g., hundreds in 1976, 592 in 1983 on Lake Michigan; Brand et al. 1983, 1988). New outbreaks of avian botulism Type E are now regular on Lakes Erie, Michigan, and Ontario and are related to interactions with introduced species (see Conservation and Management). Systemic bacterial infections have been found by M. Pokras (pers. comm.), and aspergillosis is common, especially in captive birds, and in wild birds as secondary infections (Locke and Young 1967, McIntyre 1988a, Franson and Cliplef 1993).

Body Parasites

Various parasite loads have been described in the scientific literature. A number of internal helminthes have been described including digenean trematodes (Trematoda), tapeworms (Cestoda), spiny-headed worms (Acanthocephala) and round worms (Nematoda). Trematodes were 2-3x more prevalent than cestodes; however, the severity of the infestation from cestodes was more severe than from trematodes (Chafel and Pokras 1993). None of the chicks in this study exhibited gross parasites or parasitic lesions (although 80% had internal parasites). Conversely, Kenow et al. (2003a) found that high internal parasite loads likely contributed to the mortality of two chicks in Wisconsin. Microphallid trematodes were the proximate cause of hemorrhatic enteritis in Florida’s Gulf Coast loon die-off in 1980’s (R. Stroud and R. Lange, unpubl. Data). Blood sucking ectoparasites such as mites (Acarina), lice (Phthiraptera) and flies (Diptera), including black flies, are also parasitic on loons (Storer 2002).

Leucocytozoon and Plasmodium are blood parasites found in loons (Cooney et al. 1995, Weinandt 2006). Weinandt (2006) using molecular techniques found Leucocytozoon in 40-65% of the blood samples tested (N= 57 loons), depending on conservative or liberal interpretation of the bands. There was no significant difference in Leucocytozoon intensities between chicks and adults. The presence and intensity of Leucocytozoon in adult loons was significantly explained by loon blood mercury levels (Weinandt 2006).

Causes Of Mortality

Young killed by predation (Yonge 1981, Paruk et al. 1999), starvation of submissive chick (Dulin 1988), trauma (e.g., sibling conflict; JFB, JDP, DCE), infections, and boat and water ski accidents (Pokras et al. 1993). Wounds inflicted by adults of either sex to each other during territorial conflict, or by non-parental adults to chicks, can lead to eventual death and in dense populations, can be a significant factor (M. Meyer and W. Piper, pers. com., DCE). Parasite infestations, e.g., nematodes in proventriculus and cestodes in intestines, cause mortality in all ages and sexes. Chick parasites, if severe, can prevent normal intestinal function by occluding the intestinal lumen. At least one tapeworm (Ligula intestinales) is ingested with prey fish; does not seem to be digested by the loon gut, and chicks cannot always void it in time to prevent trouble (JFB).

Multiple causes include die-offs from botulism (Brand et al. 1983, 1988), mercury poisoning in areas highly contaminated by point sources (DCE), aspergillosis (Franson and Cliplef 1993), fish nets and traps (Carey 1993), oil spills (Sperduto et al. 2003), and shooting (McIntyre 1988), and ingestion of lead fishing jigs and sinkers (Locke et al. 1982, Pokras and Chafel 1992, JFB). Lead is considered to be leading cause of recent adult mortality (Pokras et al. 1993; see also Conservation and Management: contaminants).

Young chicks susceptible to underwater predators (e.g., snapping turtles, bass, muskellunge) and avian predators (e.g., Bald Eagle; Paruk et al. 1999). Adults have few known natural predators on breeding grounds although they are vulnerable to eagle predation while incubating (Vliestra and Paruk 1997); marine predators largely unknown (see Behavior: predation).

Human/Research Impacts

Direct and indirect human impacts are many and include shooting, trapping, contaminants (particularly mercury and lead, but problems with synthetic compounds such as poly-brominated diphenyl ethers (PBDEs) and perflorinated chemicals (PFCs) are potentially problematic and poorly quantified), acid rain, fishing nets and traps, unmanaged changes in water levels on reservoirs, oil spills, shoreline development, recreational activities, climate change, disease, and emaciation syndrome (see Conservation and Management; also Evers 2007).

Rigorous research involving capture, sampling, and banding of > 4,000 adults and > 2,000 juveniles > 4 wk of age has had no short- or long-term impacts on individuals or populations (DCE, M. Meyer pers. com., W. Piper pers. com.). Marking of juveniles < 2 wk of age requires careful consideration. Toe-banding of chicks (McIntyre 1977) led to predation of chicks by Herring Gulls during interval between being released after banding and rejoining parents.

Range

Initial Dispersal From Natal Site

Slow to colonize new areas. Observations of initial returns of banded juveniles to breeding areas > 3 yr later showed an average return distance of 13 +/- 16 km and up to 92 km from their natal lake in Michigan and Minnesota (Evers et al. 2000, DCE). In Wisconsin, a similar dispersal pattern of >3 yr olds was found averaging 16 +/- 21 km, with females tending to disperse farther than males (N=38, W. Piper, pers. com.). Returning young represent the primary population component to colonize new areas. Breeding adults generally do not move beyond 4 km from their previous-year’s breeding territory and have not been recorded dispersing beyond 21 km (Evers 2001).

Females tend to move farther (average 4 km, range 0.5-20.3 km) than males (average 3 km, range 0.4-20.5 km) among a group of 103 usurped established territory holders that were located one year later (Evers 2001). Males from this group were more likely to remain within their neighborhood (an area defined by the carrying distance of a yodel call). Established territories were more likely to occur near former territories than in areas where territories were not successfully established in the past (i.e., non-territorial outcomes) (Evers 2001). Usurped territory holders were less likely to breed the following year, indicating at least a temporary cost of dispersal.

Fidelity To Breeding Site And Winter Home Range

Fidelity in breeding territories. Between-year territory fidelity of breeders best explained in a spatially-explicit context, examined by sex and territory. Territories may be divided into three types: multiple, whole, or partial territories. From 1989 to 2009, > 2,000 breeding adult loons (52% males and 48% females) from 505 territories on 313 lakes in New England and the Upper Great Lakes were color marked and followed for one to 17 subsequent years (Evers 2001, DCE). Between-year fidelity increased from multiple-lake to partial-lake to whole-lake territories in New England; and breeding adult loon territory fidelity was highest in whole-lake territories in the Upper Great Lakes. No significant differences exist in overall territory fidelity between sexes (80% in males, 82% in females). Between-year territory fidelity may indicate habitat quality and even predict declining population trends, therefore useful as a high resolution, long-term population monitoring tool for early detection of acute and chronic stressor events (Evers 2001).

Fidelity in winter territories. Between-year winter site fidelity is relatively unknown, but may be high for adults. Morro Bay, California is the only annually monitored site; 75 individuals banded from 2004 to 2009 (D. Long, pers. com.). Of these, 9 of 12 adults (75%) were observed at least during the subsequent winter, while only 5% of the 63 young-of-the-year returned the subsequent winter. One- and two-year olds do not experience a mid-winter flightless period, are more mobile, and therefore exhibit less site fidelity than adults.

Home Range

Range or territory size highly variable, depending on territory quality, particularly prey availability and nest site availability. Lake size and configuration dictate density. Uses an overall habitat use pattern that follows Pulliam and Danielson’s (1991) “ideal pre-emptive distribution” model in which an individual selects the best available site and prevents other individuals from occupying that site (DCE). There are three types of territories: multiple lake territory (MLT), whole lake territory (WLT), and partial lake territory PLT) (Evers 2001).

Based on Piper et al. (1997b), territorial pairs occupying lakes less than 24 ha require at least two or more lakes (i.e., MLT). Lake-size limits are driven by physical “take-off” requirements and ready access to nearby lakes where breeding adults can forage. Lower lake-size limits are recorded as 4.4 ha and 5.2 ha in Michigan (Miller and Dring 1988, Evers et al. 2000, respectively), and 6.4 ha in Wisconsin (Zimmer 1979).

WLT pairs remain on nesting lake throughout the breeding cycle and may share lake with non-breeding adults but not with another territorial pair. WLT pairs rarely occupy neighboring lakes.

PLT pairs share their lake with other territorial pairs. The proximity of territorial pairs on larger lakes depends on lake configuration, nest site abundance and juxtaposition, and prey availability. The minimum lake size required to support two territorial pairs was measured as 101 ha in Wisconsin (n=1,746 lakes; Zimmer 1979), 118 ha in Maine (n=133 lakes; Evers 2001a), and 124 ha in New Hampshire (n=136 lakes; LPC, unpubl. data).

Population Status

Total population abundance and population trends are well known in the contiguous U.S. They are less well known, but have recently been quantified for Alaska, the Canadian Provinces, Greenland, and Iceland (Evers 2007; Appendix 3). Population estimates are speculative in Canada because they are extrapolated from loons counted during general aerial waterfowl surveys that may not emphasize loon observations or represent the best survey time periods for loons.

Abundance trends based on Breeding Bird Survey Routes (BBS) are not used here because (1) BBS routes poorly reflect loon population trends (Robbins et al. 1986), (2) higher resolution monitoring data available for populations in the United States, and (3) BBS routes in core Canadian breeding range are rare or non-existent.

Numbers

Global population is relatively healthy and robust, with a total estimated breeding population of 252,000 to 264,000 territorial pairs (Appendix 3). The non-breeding cohort increases total adult population to 607,000 to 635,000 individuals. Population increases to 710,000 to 743,000 individuals during fall migration after including young of the year. Approximately 30% of the fall population migrates to the Pacific Coast and 70% to the Gulf of Mexico and Atlantic Coast. Over 94% of the breeding loon population resides in Canada.

North American winter range of Pacific Coast populations. Pacific Coast winter populations likely encompass breeding populations from Montana, Saskatchewan, western Nunavut, and Northwest Territories, west to the Coast. Based on the estimated number of breeding loons and information on migratory movements, approximately 215,000 to 221,000 loons (184,000 to 189,000 adults and 31,000 to 32,000 juveniles) comprising 30% of the total population over-winter on the Pacific Coast.

North American winter range of Atlantic Coast populations. On the Atlantic Coast, Common Loons overwinter from Newfoundland south to Florida, west through the Gulf of Mexico to Texas and south to central Mexico. Atlantic Coast winter populations likely represent breeding populations from Manitoba, eastern Nunavut, North Dakota, and Minnesota and all areas east. Based on the estimated number of breeding loons and information on migratory routes, approximately 495,000 to 522,000 loons (423,000 to 446,000 adults and 72,000 to 76,000 juveniles) comprising 70% of the total population over-wintering on the Atlantic Ocean.

European winter populations. A small number of individuals (<1%), approximately 3,500 to 4,500, over-winter in the United Kingdom (Lack 1986) and even smaller numbers are scattered across w. Europe coastlines, including Iceland (Snow and Perrins 1998). Breeding loons from w. Greenland likely over-winter along the w. Atlantic coast, while individuals from e. Greenland and Iceland probably over-winter along the coast of w. Europe (primarily the UK). Loons over-wintering in Iceland may represent both e. Greenland (Gudmundson 1972) and Iceland breeding populations (A. Peterson, pers. com.).

Breeding populations in Alaska. Alaska has the largest breeding population in the U.S. Estimates based on waterfowl aerial surveys of National Wildlife Refuges (Groves et al. 1996) and other areas indicate 3,600 to 6,000 territorial pairs (Tankersley and Ruggles 1993). Breeding population primarily restricted to southern, forested portions. Densities are greatest in the lakes region of the Kenai and Alaska peninsulas; considerably lower across much of central and eastern Alaska, and nearly absent north of the Brooks Range and in tundra habitats elsewhere (Groves et al. 1996). Distribution and density have changed little in the past century, with the exception of increasing local pressures and loss of breeding habitat in the Anchorage Bowl and Mat-Su Valley areas.

Breeding populations in British Columbia. Current estimates based on extrapolations from aerial waterfowl surveys suggest 25,000 territorial pairs (A. Breault, pers. com.). Breeds throughout, with centers of abundance in the southwestern and southern parts, including the Thompson-Okanagan and Fraser Plateaus and the Fraser Basin region (Campbell et al. 1990, 2008). Commonly breeds on large coastal islands, including Vancouver and Queen Charlotte, and less frequently on small coastal islands. Historical declines or range retractions have not been recorded. Limited BBS routes indicate a significant population increase from 1967 to 1998 (Scheuhammer et al. 2003).

Breeding populations in far northern Canada. An estimated 50,000 territorial pairs occur across the northern tier of Canada; with centers of abundance in the Mackenzie and Keewatin Districts of the Northwest Territories. Population estimates are rough extrapolations from aerial surveys and population trends are relatively unknown. Within this large region, considered rare in the Yukon with most observations occurring in south (Vogel 1997). Low abundance estimates for loons along the Yukon coastal plain are supported by an early 1970 survey that documented fewer than 10 individuals (Johnson and Herter 1989). Similar low abundances have been documented by intensive surveys along the Alaskan coastal plain (Larned et al. 2001). In the Northwest Territories and Nunavut, generally restricted to forested areas (Godfrey 1986); and some breeding records on the Beaufort Sea coastal plain exist but are rare (Johnson and Herter 1989). Exceptions to these low abundances are in n. Quebec and on s. Baffin Island’s tundra (Godfrey 1986).

Breeding populations in the western contiguous U.S. Historically nested across the northwestern U.S. in small and discontinuous numbers. A handful of nesting records exist for n. California and w. Oregon, but apparently extirpated there for several decades (Corkran 1988). Nearly 100 territorial pairs occur in four western states: Idaho, Montana, Washington, and Wyoming. In Idaho, at least 12 lakes historically had nesting pairs of loons (Fitch and Trost 1985). Except for a territorial pair straddling the Wyoming-Idaho border (nest in Wyoming), apparently extirpated in Idaho by mid-1900s. First successful loon breeding record in recent times was documented in the Idaho panhandle on Lake Pend Oreille (Taylor 2001). In Montana, appears to be stable or slightly increasing, where current population is concentrated north of Missoula and west of the Continental Divide. Highest concentrations in Tobacco-Stillwater drainage, the Clearwater-Swan drainage, and in and near Glacier National Park ( 20-30 territorial pairs; S. Gniadek, pers. com.).

Washington has a poorly substantiated historical record of breeding; nesting records exist for both sides of the Cascade Mountains (Richardson et al. 2000). Urban development near Seattle and Tacoma has displaced breeding pairs from several lakes, but protection of shoreline habitat around several municipal water supply reservoirs supports nesting pairs. In ne. Washington, a single breeding pair in the Okonogan highlands was first located in 1985. Since then, the number of loon pairs has slowly grown (D. Poleschook and G. Gumm, pers. com.). Washington’s breeding population has rebounded from severe lows in the early and mid 1900s.

Wyoming historical breeding distribution and abundance is similar to current record, primarily because Yellowstone National Park (YNP) and the Shoshone National Forest (SNF) have effectively protected lake habitat; 12-18 territorial pairs in YNP (T. McEneaney, pers. com.), approximate 7 territorial pairs in SNF, with some use of Grand Teton National Park (Cerovski et al. 2000).

Breeding populations in the Prairie Provinces. A total of 12,500 to 15,000 territorial pairs found in Manitoba, Alberta, and Saskatchewan. Generally widespread but limited to the northern parts of the provinces. Population declines in some of the highly populated areas have occurred (McNicholl 1988). Alberta and Saskatchewan population estimates are substantially lower than estimates in Manitoba. In Alberta, population estimates are rough and not based on standardized monitoring. Breeding populations better known in Saskatchewan than other prairie provinces owing to detailed breeding bird atlas (Smith 1996). Breeding loons distributed throughout the northern and central parts south to Redberry Lake, Yorkton region, Nickel Lake, and Moose Mountain (Smith 1996). Similar to s. Alberta, lakes south of these areas are often shallow and have poor fish stocks. In Manitoba, found province-wide, except for the prairie areas to the south, and concentrations appear to be greatest in west-central. Yonge (1981) conducted a study on Hanson Lake, Saskatchewan (just west of the Manitoba border) and documented a high density of 10 pairs per 405 ha, typical of lakes in this area.

Breeding populations in the U.S. Great Lakes. Here, populations have suffered greatest decline in historical range and currently in the greatest need for increased conservation efforts. Breeding populations are extirpated in Illinois, Indiana, Iowa, and Ohio and restricted to the northern portions of Minnesota, Wisconsin, and Michigan (Evers 2007). Despite these declines, the U.S. Great Lakes region supports over half of the loon breeding population in the entire U.S. (5,900 to 7,200 territorial pairs), and three-quarters of the breeding population within the contiguous U.S. (Appendix 3). In Michigan, concentrations of suitable lake habitat in the southeastern and southwestern parts of the state formerly supported many territorial pairs (Barrows 1912). Breeding populations best protected on federal lands, including Seney National Wildlife Refuge, Hiawatha and Ottawa National Forest, and Isle Royale National Park. In Wisconsin, the number of adult loons is estimated at 3,131 +/-278 in 2000 (Gostomski and Rasmussen 2001). Breeding range historically extended from the southern counties northward (Kumlien and Hollister 1951), but today is restricted to the northern third of the state. North-central Wisconsin, particularly the two-county area including Oneida and Vilas, has the greatest concentration of breeding loons (Meyer 2002).

In Minnesota, the first statewide population estimate in 1989 calculated 11,626 +/- 1272 adult Common Loons (Strong and Baker 2000); subsequent standardized monitoring efforts for six, 100-lake index areas (based on protocols by Hanson 1996) show no significant declines from 1994 to 2002 (Baker 2000, MLMP 2002). The breeding range of loons in Minnesota historically extended south to the Iowa border and west to the Red River Valley (Janssen 1987). Today, found across the northern two-thirds of the state (north of the Minnesota River) with the greatest density in the north-central and northeastern regions (Hanson 1996, Strong and Baker 2000). Several breeding populations have been well studied in Minnesota including those in the Boundary Waters Canoe Area (Olson and Marshall 1952), Itasca State Park (McIntyre 1975), and Voyageurs National Park (Reiser 1988, Paruk et al. 2008).

Breeding populations in Ontario and Quebec. Well over half of North America’s breeding population is found in Ontario and Quebec. Ontario has more loons than any other Canadian province and contains over one-third of the global breeding population with an estimated 97,000 territorial pairs (Wayland and McNicol 1990). Historically, loons occurred across Ontario and even nested on Lake Erie; today, however, they are nearly absent as a breeding species from the Carolinian Forest Zone of sw. Ontario (Cadman et al. 1987). Densities are lowest along the Hudson Bay lowlands and far northern Ontario, highest in the Precambrian Shield area. High population densities continue into western and central Quebec, where most of that province’s 50,000 territorial pairs occur. Densities are lower in e. Quebec, including the Ungava Peninsula (McNicholl 1988). Breeding Common Loons are rare within Quebec’s Hudson and James Bay lowlands. Because there are few lakes, loons are nearly absent within the lower St. Lawrence River watershed. Common Loon densities are also low in the relatively treeless landscape along the north shore area of the Gulf of St. Lawrence.

Breeding populations in New England and New York. Breeding loon populations in the northeastern U.S. have experienced severe historical declines and range retractions. Historically, the southern periphery of the loon’s breeding range included e. Pennsylvania and Connecticut (McIntyre 1988).

Today in New England and New York, nearly 2,250 territorial pairs are currently distributed across much of their historical range. Extirpated in the early 1900s, breeding loons recolonized Massachusetts in 1975 (Blodget and Lyons 1988) -- first found on the Quabbin Reservoir and across central Massachusetts; breeding pairs have increased to a total of 24 territorial pairs (Savoy 2004b).

In New Hampshire, the number of territorial pairs has more than doubled from 87 in 1980 to 247 in 2008 (LPC, unpubl. data). The core breeding area is Squam and Winnipesauakee lakes and surrounding smaller lakes. Loons have recolonized and continue to expand throughout southern New Hampshire, and have reoccupied much of northern New Hampshire, north of the White Mountains (Brennan 2003), where loon numbers dropped to historical lows in the mid-1970s. For example, in 1976, only eight territorial pairs were found on Lake Umbagog in northern NH. By 2000, 31 territorial pairs were found there (Evers 2002).

In Vermont, only 12 territorial pairs were known in 1983, but by 2002 a total of 59 territorial pairs were counted, including five pairs in s. Vermont. Currently, there are no territorial pairs on Lake Champlain and little or no evidence of historical nesting there (Hanson et al. 2002).

In Maine, the species was more protected from historical human disturbance than in nearby New England states. Still, southern areas of Maine experienced declines in the number of loons in the mid-1900s (Cross 1979, Sawyer 1979). Current estimates are based on a stratified random sample conducted by the Maine Audubon Society for the southern half of Maine and a random aerial survey conducted by the Maine Department of Inland Fisheries and Wildlife for the northern half. Combining both surveys creates an estimate of a statewide adult loon population numbering 4,100 (or 1,700 territorial pairs) (Appendix 3).

New York experienced historical declines similar to other Northeast breeding loon populations. Loons historically nested in the Finger Lakes (McIntyre 1979) and across ne. New York. By the late 1970s, McIntyre (1979) documented a 35% decline in the number of lakes with nesting loons. Breeding populations were restricted to nine counties representing the Adirondack Mountains and the Thousand Island area of the St. Lawrence River and accounted for an estimated 155 territorial pairs (McIntyre 1979). Trivelpiece et al. (1979) estimated fewer than 200 territorial pairs during that same time period. In the mid-1980s, Parker and Miller (1988) estimated 216 to 270 territorial pairs, including some pairs on lakes south of the St. Lawrence River and outside of the Adirondack Park. Today, estimates are similar and breeding populations continue to expand geographically; the species has now reoccupied areas in central and western New York (Schoch 2008).

Breeding populations in the Canadian Maritimes. The total number of loons in this four-province area is speculative because the numbers of loons in Newfoundland is unknown. Both Nova Scotia and New Brunswick have breeding populations of approximately 1,200 pairs in each province. Erskine (1992) estimated that this is one-third to one-half of the species’ historical abundance, although loons remain widely distributed in these provinces. In Nova Scotia, concern exists over apparent population declines (N. Burgess, pers. com.); areas with few lakes and low loon densities contain sedimentary parent material similar to eastern New Brunswick and western Cape Breton (Erskine 1992). Prince Edward Island has few lakes and provides habitat for one loon pair (J. Kerekes, pers. com.). New Brunswick population trends appear stable or even slightly increasing (Stocek 1993). Although they are known to occur throughout the province, loons are comparatively less common in n. Labrador (N. Burgess, pers. com.) than in other eastern provinces.

Breeding populations in Iceland and Greenland. Loons breeding on these two islands nest only on non-forested lakes, a habitat type that is rarely used in most other parts of their range. The Icelandic breeding population is relatively well-known (A. Peterson, pers. com.); it is widely distributed and has not changed markedly in recent years. Little is known about the loon distribution and population trends for Greenland, where estimates are based on loon densities from a small area and extrapolated across suitable habitat (D. Boertman, pers. com.). Breeding loons are thought to be distributed solely along the outer margins of the southwestern and southeastern parts of the island (D. Boertman, pers. com.).

Trends

For details, see Numbers, above. Numbers decreased substantially across southern range limit during early to mid-twentieth century (McIntyre 1988a). Although recent population trends for the large breeding loon populations in Canada are difficult to estimate due to survey limitations, results from winter counts suggest that total loon numbers are steadily increasing and the breeding loon population has been recovering since the mid-1900s (Evers 2007).

Overall population trends for breeding populations in the United States generally follow trends in Canada. Substantial increases in New England and other parts of the U.S. are documented since the mid to late 1900s. Current breeding populations in Michigan and Washington are less stable. For state and province-specific trends, see Numbers, above.

Population Regulation

Factors limiting populations need study. High mortality in first 2-3 years of life: see Lifetime reproductive success, above. Nests and young vulnerable to predation, which can significantly limit reproduction in some areas (see Behavior: predation). Species is slow to colonize new breeding areas; see Range, above. All these factors contribute to limiting populations. For population models, see Measures of Breeding Activity: lifetime, above.

Significant non-breeding component to many populations. Not all adults that return to their breeding area attempt to nest or even establish a territory. Approximately 46% of the summer adult loon population in New Hampshire does not attempt to nest (LPC unpubl. data). Some loons establish territories but do not attempt nesting, while other loons are sub-adults that have yet to breed (primarily < 6 yr old) or older adults that have been displaced from established territories.

On average, 68 +/- 6% of established territorial pairs attempt nesting in New Hampshire (Taylor and Vogel 2003); the 3-year rate in Saskatchewan is 77% (Yonge 1981). Non-nesting pairs guard their territory through the breeding season. In New Hampshire, the average buffer, or non-territorial, population is 19% (LPC, unpubl. data). Non-territorial holders spend their summers in common-use areas and frequently intrude on established territories.

Generally, long-term studies of individually-marked birds (representing multiple and diverse orders) indicate 15-20% of breeding individuals provide over half the young that survive to become breeders (Newton 1992). Evidence indicates that loons follow this pattern in the Rangeley Lakes area of Maine, with approximately 19% of breeders producing half of the fledged young (BRI, unpubl. data; 1995-2002).

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