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Common Loon
Gavia immer
Order
GAVIIFORMES
– Family
GAVIIDAE
Authors: Mcintyre, Judith W., and Jack F. Barr
Revisors: Evers, David C., and James D. Paruk

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Migration

Figure 2. Common Loon migration.

Nature Of Migration In The Species

Medium-distance complete migrant; not known to remain on breeding lakes throughout the year. Most of population shifts from freshwater inland breeding locations to coastal marine wintering locations, although some remain at inland freshwater sites throughout winter. Sub-adults may remain at wintering sites throughout the year.

Timing Of Migration

Spring

Generally Mar–Jun; timing varies slightly but is remarkably synchronous throughout range. Spring migration independent of mate because pair bonds do not persist beyond the breeding season (DCE). Spring arrival to nesting lakes depends largely on the timing of ice-out. While some individuals arrive in the southern periphery of their range in mid- to late March (i.e., Washington, sw. Michigan, and s. New England), loons generally begin moving en masse in early to mid-April along both the Pacific and Atlantic coasts.

Large congregations of loons assemble in the northern end of the Gulf of Mexico in early April. Spring migration peaks in early May in the northern Great Lakes (Ewert 1982). Migrants generally congregate on large waterbodies, including the Great Lakes and Mississippi River, and conduct daily reconnaissance flights to their nesting area.

In Cape May, NJ, migrates through late May (rarely through early Jun; Sibley 1993); in Massachusetts, mid-Mar–early Jun, with peak late April-mid May (Veit and Petersen 1993); in Minnesota peaks from mid-April through early May (Janssen 1987); in Missouri, migration begins mid-Mar, peaking late Apr–early May, with stragglers through late May (Robbins and Easterla 1992); in Ohio, late Mar–late May (Peterjohn 1989); in Colorado, peaks mid- to late Apr (Andrews and Righter 1992); in California peaks mid-Apr (Small 1994); in s. British Columbia occurs from mid- to late Mar to Jun, peaking late Apr–early May (Campbell et al. 1990).

Timing and factors responsible for migration not studied. Evidence indicates photoperiod determines general timing of northern migration and other cues control initiation. Loons are well known for arriving at breeding lakes soon after ice is out (often returning when lakes are only partly open). They will congregate in open bodies of water, including rivers, as they proceed northward. Reconnaissance flights are usually made from open water to territorial waters. As they arrive at their breeding territories, males may precede females by several days, particularly along the southern periphery of their range (DCE). In northern latitudes, initial arrival may be more uniform. In general, established territories are filled before transitional territories.

Fall

At the end of the breeding season, adults migrate independent of their chicks and of each other. Local or social flocking starts in late-summer, usually on large lakes or lakes that contain unsuccessful territorial pairs (Paruk 2006). Fall migration generally begins in September at high latitudes and October in low latitudes, and by late November most migrants have arrived in their wintering areas. Peak migration in the lower Great Lakes ranges from late October to late November (Svingen 2000).

Migration dates: in s. British Columbia, late Aug–late Nov, peaking first half of Oct (Campbell et al. 1990); in California, mid-Sep–late Nov (Small 1994); in Colorado, peaks mid-Oct–late Nov (Andrews and Righter 1992); in Ohio, generally begins mid- to late Oct, peaking in Nov (Peterjohn 1989); in Missouri, begins mid-Oct, peaking in early Nov (Robbins and Easterla 1992); in Minnesota, peak is in mid Oct (Janssen 1987); in Massachusetts, late Aug–Dec (Veit and Petersen 1993); in Cape May, NJ, early Sep (or earlier) to early Nov (Sibley 1993).

Routes Of Migratory Movement

Based on extensive banding efforts by researchers at BioDiversity Research Institute in Maine, Wisconsin Department of Natural Resources, and George Mason University in California, as well as tracking via satellite transmitters (Kenow et al. 2002, 2009), migration routes are now well described. An estimated 710,000 to 743,000 loons initiate fall migration (including approximately 607,000 to 635,000 adults and 103,000 to 108,000 juveniles) (Appendix 3). The estimate of migrating adults is based on breeding loon counts, and the number of juveniles is based on a 25-year statewide dataset in New Hampshire that shows 17% of the fall loon population is comprised of young-of-the year (Taylor and Vogel 2003).

The major known migration routes and staging areas have been identified through observations (Svingen 2000), band recoveries (McIntyre 1988, Evers et al. 2000, BRI unpubl. data) and satellite telemetry (Kenow et al. 2002, 2009; Yates et al. 2002). A map of migration routes connecting breeding and wintering areas has been constructed using band recoveries, satellite telemetry location information, morphometric data, and known migratory movements (Figure 2).

Migratory movements along the Atlantic Coast occur in both coastal and offshore areas (Powers and Cherry 1983) and likely represent breeding populations from the Canadian Maritimes, far e. Quebec, Newfoundland, and w. Greenland breeding populations. The very large loons in Maine, New Brunswick, and e. New Hampshire do not migrate far and primarily over-winter in the Gulf of Maine (Kenow et al. 2009; DCE), while smaller loons from other New England and New York breeding populations migrate to Long Island Sound south to New Jersey (Kenow et al. 2009). Large numbers of fall migrants originating from Ontario and Quebec stage on Lake Ontario (Ewald and Sherony 2000), move through the Finger Lakes area of New York (Evans et al. 1994), and arrive in Chesapeake Bay. Their arrival regularly coincides with fall movements of a favored prey species, Atlantic menhaden (Brevoortia tyrannus) (Spitzer 1993).

The loon populations of the Upper Great Lakes in Michigan and Wisconsin migrate along the southern Great Lakes and use an overland migration route to the Gulf of Mexico (Alabama east along the Florida coast) and e. Florida. Some individuals stage on lakes along the way and even over-winter in larger reservoirs in Tennessee (Kenow et al. 2002) and Alabama (Belant et al. 1991). Minnesota and Wisconsin breeding populations have two migration routes, and both generally use the Great Lakes as staging areas. The primary route includes the Gulf of Mexico from Mississippi west to Texas, and the second documented route uses the southern Great Lakes to make an easterly migration to the mid-Atlantic (Eberhardt 1984, Evers et al. 2000, Kenow et al. 2002).

Mid-continent loon populations in Manitoba, w. Ontario, and likely e. Nunavut travel eastward, using Hudson Bay and the Great Lakes as staging areas, and then move southeastward to the mid-Atlantic (McIntyre 1988, BRI Unpubl. data). Some loons that likely originate in e. Manitoba-w. Ontario are known to use large lakes in Minnesota such as Mille Lacs (McIntyre and Barr 1983) and Winnibigoshish. A loon banded in Flin Flon, Manitoba and recovered in Pennsylvania (M. Wayland, pers. com.) further defines the western edge of breeding populations that overwinter along the Atlantic Coast.

Mid-continental breeding populations found in areas such as central and northern Saskatchewan use a migration route that crosses the Rocky Mountains in Montana and remains east of the Sierra Nevada Mountains, using lakes such as Walker and Pyramid in Nevada and Flaming Gorge Reservoir on the Utah-Wyoming border for both spring and fall staging areas (based on satellite transmissions from five loons; Yates et al. 2002). The interim migratory population that uses Flathead Lake in Montana for a fall stopover over-winters on both sides of the Baja Peninsula (B. Gullett, pers. com.). Western U.S. breeding loons migrate to the mid-Pacific Coast, as evidenced by Montana band recoveries from California (D. Long, pers. com.). Satellite transmissions from two breeding loons in the Kenai National Wildlife Refuge show that over-wintering areas exist within the Gulf of Alaska (J. Schmutz, unpubl. data).

Information is lacking on the migratory behavior of breeding loons from Alberta, western Nunavut, Yukon, and British Columbia along the Pacific Coast. Few loons likely make a trans-Pacific migration to the Asian coast. Eastern Greenland breeding loons likely migrate and over-winter in Iceland and other parts of western Europe in the North Sea. It is unknown whether the Icelandic breeding population remains for the winter or migrates to western Europe (A. Peterson, pers. com.).

Migratory Behavior

Fall migration is usually more protracted than spring migration. Loons are diurnal migrants and initiate long-distance migratory flights in the morning (Williams 1973, Ewert 1982, Powers and Cherry 1983). Overland migration altitudes ranged from 1,500 to 2,700 meters in New York (Kerlinger 1982), while over water loons often migrate within a few meters to 100 meters of the surface (DCE).

Unsuccessful breeders may leave breeding areas in Aug, rarely in Jul, before those with young do. Fall movement is earlier for adults than for juveniles. Parents generally migrate first, usually separately; young remain on natal or adjacent lakes after adults have departed, until near freeze-up. Marked juveniles from adjacent territories have been seen leaving together in a group (McIntyre 1975); this behavior is not uncommon. Fall migration for adults may be more directed than that of young-of-the year (Kenow et al. 2009).

Diurnal migrant (Williams 1973). Flights may include thousands of irregularly spaced individuals (McIntyre 1975, Winter and Morlan 1977, Kelling 1996), or migrants may fly alone or in small groups. During migration, may assemble at inland sites and offshore in large groups from a few individuals to hundreds (Peterjohn 1989, Veit and Petersen 1993). In s. New Jersey, flies at height of ≥15 m over water, higher overland (Sibley 1993), but Kerlinger (1982), using radar, found mean altitude over New York of 2,057 m above ground level (range 973–2,167 m, n = 24).

Migratory staging is common throughout range, in both spring and fall. Concentrations (hundreds to thousands) in Minnesota (McIntyre and Barr 1983), Great Lakes (Perkins 1965), Walker Lake, NV (L. Neel pers. comm.), Twin Lakes, ID (JDP), and Chesapeake Bay (Spitzer 1993).

Simultaneous arrival of adjacent territory holders occurs in southern part of range. Older birds arrive first, often occupying partly thawed territorial lakes; young adults arrive last, mid-May–Jun (DCE). Age-related spring migration sequence may be influenced by readiness to fly following remigial molt, which advances each year for first few years (see Appearance).

One- and two-year olds remain throughout year on wintering sites south to central Florida and nw. Mexico, but increase in number toward northern portion of winter range; non-migratory birds may include oiled and injured individuals (Veit and Petersen 1993).

Control And Physiology

Heavy concentrations of migrants occur when tailwinds provide advantage (Kerlinger 1982). Heaviest fall flights in n. Ohio were observed when northwesterly winds followed passage of a cold front (Peterjohn 1989). Hormonal regulation and orientation methods unknown.