Nature Of Migration In The Species
Medium-distance complete migrant; not known to remain on breeding lakes throughout year. Most of population shifts from freshwater inland breeding locations to coastal marine wintering locations, although some remain at inland freshwater sites throughout winter. Subadults may remain at wintering sites throughout year.
Timing And Routes Of Migration
Generally March-June; timing varies slightly but is remarkably synchronous throughout range. In Cape May, New Jersey, migrates through late May (rarely through early June; in Massachusetts, mid-March-early June;in Missouri, migration begins mid-March, peaking late April-early May, with stragglers through late May;in Ohio, late March-late May; in Colorado, peaks mid- to late April;in California peaks mid-April; in s. British Columbia occurs from mid- to late March to June, peaking late April-early May.
September-December, but inland wintering birds usually evacuate these sites (often regardless of whether they have frozen) by February. Migration dates: in s. British Columbia, late August-late November,peaking first half of October;in California, mid-September-late November;in Colorado, peaks mid-October-late November;in Ohio, begins mid- to late October (scattered earlier records),peaking in November;in Missouri, begins mid-October, peaking in early November;in Massachusetts, late August-December; in Cape May, New Jersey, early September (or earlier) to early November.
Routes Of Migratory Movements
Incompletely known; needs study. East Coast flights reported just offshore following coastline, as well as overland. Powers and Cherry (1983) mapped significant offshore and inshore Atlantic flights, both spring and fall, and proposed that inshore and offshore components represent different breeding populations. In Cape May,largest numbers of spring migrants pass offshore, where they may stage (e.g., more than 1,000 observed 80-90 km offshore 8 March 1987). Migrants fewer but regularly observed inland (e.g., Hawk Mtn., Berks Co., Pennsylvania). Ohio fall migrants seen along Lake Erie flying south or east. Significant numbers funnel over Whitefish Point on Lake Superior, north in spring; peak dates early May.
On West Coast, hundreds to thousands fly past Pigeon Point, San Mateo, California during April. Western inland routes still unclear, but significant numbers through w. Nevada, especially Walker Lake, Mineral County.
Unsuccessful breeders may leave breeding areas in August, rarely in July, before those with young do. Fall movement earlier for adults than for juveniles. Parents generally migrate first, usually separately; young remain on natal or adjacent lakes after adults have gone, until near freeze-up. Marked juveniles from adjacent territories have been seen leaving together in a group;uncertain if this behavior is typical.
Diurnal migrant. Flights may include thousands of irregularly spaced individuals,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. In s. New Jersey, flies at height of ?15 m over water, higher overland, but Kerlinger (1982), using radar, found mean altitude over New York of 2,057m above ground level (range 973-2,167, n = 24).
Migratory staging is common throughout range, in both spring and fall. Concentrations (hundreds to thousands) in Minnesota,Great Lakes,Walker Lake, Nevada, and Chesapeake Bay.
Simultaneous arrival of adjacent territory holders in southern part of range suggests that summer neighbors may winter together. Older birds arrive first, often occupying partly thawed territorial lakes; young adults arrive last, mid-May-June. Age-related spring migration sequence may be influenced by readiness to fly following remigial molt, which advances each year for first few years.
Immatures remain throughout year on wintering sites south to central Florida and nw. Mexico, but increase in number toward northern portion of winter range; nonmigratory birds may include oiled and injured individuals.
Thanks to Mcintyre, Judith W. and Jack F. Barr. 1997. Common Loon (Gavia immer), The Birds of North America Online (A. Poole, Ed.),species no.313.
From Iceland and Greenland main departures, singly or in small parties, September-October, though some winter southern coasts. Minority reach winter quarters (e.g. Scotland) from mid-August, probably mainly immatures or failed breeders. Infrequent records of family parties on north Scottish coasts, August perhaps from local breeding, since by then juveniles hardly capable of sustained flight for minimum 800 km crossing from Iceland, while possibly family bond broken before autumn migration. Freezing of freshwater lakes over most of breeding range results in maritime winter distribution. Spring return early May to mid-June according to latitude and weather, remaining in bays and fjords until thaw of inland ice. Pre-breeders summer chiefly in northern coastal waters, some regularly in Shetland, but seldom North Sea.
Migrations little understood in absence of European ringing recoveries. West Palearctic winterers may be mainly of Icelandic origin, but some probably from Greenland or even Canadian Arctic: one Faeroe Islands c. 1860 contained Eskimo arrow, and others collected Iceland in winter had ingested grit not of Icelandic origin. Winters regularly, though numbers relatively small, around Britain and Ireland and in North Sea; irregularly east to Varanger Fjord and Latvia, and south to Azores, west Mediterranean, and Madeira. Casual to inland European waters; Black Sea reports erroneous.
Thanks to BWP on CD-ROM