Red-throated Loon Gavia stellata
Version: 2.0 — Published April 16, 2020
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Movements and Migration
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Dispersal and Site Fidelity
Natal Philopatry and Dispersal
At a breeding site in northwestern Alaska, 9 of 13 fledged juveniles with implanted satellite transmitters migrated southwesterly toward East Asia (153). Thirty percent died before crossing the 180th meridian. Two juveniles that survived more than a year, spent winter and early summer at Hokkaido, Kunishir, and Sakhalin islands, before transmitter failure. The transmitters in the remaining 7 juveniles did not provide locations during their first summer either due to transmitter failure or interference with transmitter signals encountered at sites west of Japan. Recoveries of immature birds banded in Shetland and Orkney Islands indicated that some may return to breeding areas at second summer; among the 31 individuals banded, 8 were in breeding locales, 6 were recovered wintering off Ireland and Devon (154), and 17 were in the ocean adjacent to the natal area. Number of recoveries in natal area was higher in third summer (7 of 11; 154); none were recovered in wintering areas at that age. In Shetland Islands, the distance between fledging and later breeding sites was observed to be farther for females (mean 37.8 km, range 6–68, n = 6) than for males (mean 2.2 km, range 0.5–4.4, n = 5; 10). No inland band recoveries in freshwater habitats of 1 yr-old or 2 yr-old individuals banded in Sweden or Finland (11).
Adult Fidelity to Breeding Site and Dispersal
Territory reuse by unmarked birds is high in North America (34, 29, 27). Satellite telemetry locations from the arctic coast of Alaska showed 90% overlap of breeding home ranges (95% utilization distribution contours) between 2 consecutive summers (n = 5; 165). Adults banded on breeding areas in the United King show very high site and territory fidelity (Foula Island; 166). Of 24 marked, all were recaptured on previous the year's breeding pond except 3 males and 3 females, which were recaptured at adjacent ponds 0.11–1.05 km away (Shetland Islands; 10). Reuse of ponds within territory may be affected by success the previous year (34, but see 29); in United Kingdom, reuse is greater on ponds < 0.03 ha than on ponds > 0.03 ha (8). Data from southern Sweden, show that about 30% of breeding sites were abandoned over a 10-year period, but the loss was largely compensated by settling at new sites or return to those used in the past (5).
Fidelity to Overwintering Home Range
Individuals marked with satellite transmitters (155) showed 100% site fidelity at the scale of the North Sea between 2 winters (n = 6). Average overlap of 50% utilization distributions of winter transmitter locations between the 2 consecutive winters was 28% (range: 0–97%), and average overlap of 95% utilization distributions was 50% (range: 11–100%).
Red-throated Loons undergo a complete, medium-distance migration and are not known to overwinter on breeding lakes. Breeding adults use freshwater habitat in the summer; otherwise all age cohorts use marine habitat. Rarely observed in most wintering areas during the summer, although juveniles remain at sea throughout year. Two juveniles marked with a satellite transmitters on the Arctic Coastal Plain, Alaska, remained at the same sites where they wintered (Hokkaido, Kunashir, and Sakhalin islands) through their first summer (153). Two apparent migration routes used by breeders in Alaska: (1) arctic breeding sites to wintering sites in East Asia, (2) sub-arctic breeding sites to wintering sites along Pacific Coast of North America. Along the Pacific Coast, latitudinal pattern of wintering sites and breeding sites suggests a chain migration strategy, with wintering site latitude increasing with breeding site latitude (38). Divergent migration patterns in Alaska may reflect sea-level changes during Pleistocene glacial cycles (167, 168, 38). Along the Atlantic Coast, loons predominantly exhibit a loop migration strategy with distinct routes for spring and fall migration: coastal spring migration, then in fall, returning to mid-Atlantic wintering grounds primarily through Hudson Bay and either overland from the Lower Great Lakes to Delaware Bay or along the coast from the Gulf of St. Lawrence (39). In Eurasia, individuals wintering in the North Sea (155) migrated to breeding areas primarily in northern Russia, but also Norway, Greenland, and Svalbard. Spring migration routes to Russia and Norway showed both coastal and overland routes and fall migration followed similar routes as spring migration.
Timing and Routes of Migration
See Figure 1. Generally March through June, depending on latitude, and may continue over 4 mo. Departures from wintering sites in East Asia occurred from late March to early May (153). On British Columbia coast, small flocks evident along southern coast by late May; single birds begin to move north by early April; main movement late April–early May; individuals occasionally linger along northern coast to mid-June. Loons wintering in the mid-Atlantic began northward movements along Atlantic coast in April through early May. Along Atlantic Coast, migration peaks in March in Virginia (169), April in Massachusetts (170); usually late April in inland Ontario (171, 172); Peaks in Bay of Fundy near New Brunswick in early May (173). In May, stopovers of up to 4 weeks were common among satellite-tracked loons in Gulf of St. Lawrence and St. Lawrence River (39).
Arrival on summer range variable. In southern part of North American breeding range (Haida Gwaii, British Columbia), arrives 11–19 April (33). First sightings 5 and 11 June on the Arctic Coastal Plain of Alaska (36); for southeastern Beaufort Sea concentrations from Herschel Island to Cape Dalhousie, peak varies year to year, late May–mid-June (174). In Aleutian Islands, arrival in late April with pairs common by mid-May (94). Pairs in northern part of range arrive after mid-June (Devon Island ; Bathurst Island ); nonbreeders continue to arrive until July; early arrivals 3 June on Baffin Island and Melville Peninsula (105). Territorial occupation in Arctic within 1 d of meltwater (36, 29); until then, pairs remain on nearby ocean leads for up to 2 wk (Alaska; 35).
In the United Kingdom, populations migrate earlier. In Shetland Islands, pairs occupy territories as early as March and April (154), may stay on lakes in groups of ≤ 15 up to 2 mo until onset of breeding (55, 154). Loons from the North Sea marked with satellite transmitters started spring migration around 15 April and migration peaked on 25 May; spring migration was less likely to be initiated during windy conditions, as indicated by rough sea surface conditions (155). In Severnaya Zemlya, Siberia, 29 June is earliest arrival (129). On the Indigirka River Delta, Russia, Red-throated Loons were first observed on 14 June 1993, 6 June 1994, and 14 June 1995 (J. Pearce, personal communication).
Departure from breeding sites is likely related to reproductive success, with successful pairs departing later than unsuccessful pairs. In Alaska, breeding adults marked with satellite transmitters, but with unknown reproductive success, departed the Arctic Coastal Plain and Seward Peninsula in early September, and breeding sites farther south in mid-August (38). After fledging, juveniles marked with satellite transmitters (n = 13) apparently initiated fall migration 2 wks later than adults (153). Adults marked with satellite transmitters departed breeding sites throughout arctic and sub-arctic Canada, and northwest Greenland, in late August and early September (39).
Observations indicate departure from Simpson Lagoon, Alaska, in late August–early September (176); Bathurst Island early September (27); and Victoria Island (176), Baffin Island, and Melville Peninsula (105) mid-September. First sightings in late September–early October along Atlantic Coast. Major sightings in November along northeastern coasts: 7.4–7.8 loons/h during 5–18 November at Manomet Point, Massachusetts (177); 8,262 individuals observed 14 November 1996 at Avalon, near Cape May, New Jersey (178); > 50,000 counted there every autumn (179, 180), the timing correlated with onset of mid-arctic deep cold (181).
Along south shore of Lake Ontario, average of 7,750 individuals seen each fall 1993–1997, with median date of occurrence 22 November; peak migration 17 November–1 December (181). Inland sight records suggest the main migration route of these birds is through western Pennsylvania.
Fall migration to the North sea (155) peaked on 27 September and declined until 6 November before increasing again, the second increase likely indicated departure from molting areas. Fall migration was most likely to be initiated at temperatures between 2 and 12 °C and during periods with winds from the north. Most individuals arrived at the German Bight in the first week of January, with the earliest arrival in mid-November.
Routes of Migratory Movements
As revealed by satellite telemetry (38), breeding adults from the Arctic Coastal Plain, Alaska, marked with satellite transmitters (n = 17), traveled through the Bering Strait or overflew the Chukotka Peninsula and then migrated along the coast of the Kamchatka Peninsula and across the Sea of Okhotsk to wintering sites in eastern Japan and the southern Korean Peninsula. From breeding sites south of the Arctic Coastal Plain, loons migrated along the Pacific Coast of North America to wintering sites ranging in latitude from 60°12’ to 20°21’. Average (± 1 SD) migration distance from the Arctic Coastal Plain to wintering sites in East Asia (7,993 km ± 1,285 SD) was 2,000 km longer than those from more southern breeding sites that wintered along the Pacific Coast of North America (Yukon-Kuskokwim Delta 5,690 km ± 1,165 SD, n = 7; Seward Peninsula 5,189 km ± 1,481 SD, n = 7; Copper River Delta 4,816 km ± 1,224 SD, n = 7). Stopover sites (defined as sites intermediate to breeding and wintering sites where loons remained for ≥ 1 wk), were used by most, but not all, loons during spring and fall migrations. Likely sites of remigial molt during fall migration, as inferred from residency times of > 3 wk at fall migration stopover sites, at the Etolin Strait and Bristol Bay in Alaska, Karaga Gulf and Kronosky Zaliv in Kamchatka, Sakhalin and Hokkaido islands. Similar routes used during fall and spring migrations.
Post-fledging juveniles from the Arctic Coastal Plain of Alaska marked with satellite transmitters (n = 13) showed similar fall migration routes as adults and migrated to wintering sites in East Asia, including Hokkaido Island, the Kuril Islands, and the Commander Islands (153).
Hawkings (183) hypothesized a fall overland migration route through the Mackenzie River valley to the Pacific Northwest for loons from the Yukon coast and Mackenzie River delta, Canada. In northeastern United States, observed throughout shelf waters in spring, but farther inshore in fall (177). Annual sightings of large numbers in Bay of Fundy (173) and inland over Cayuga and Seneca Lakes, New York in November (179), point out the importance of these coastal and overland routes; the latter may represent flights from staging sites on Lake Ontario, where thousands congregate (45). Inland movements border Lake Ontario (178), moving west in fall, turning south to western Pennsylvania, and crossing eastward across Pennsylvania to Atlantic coast (181). Both routes have been documented in loons marked with satellite transmitters (39).
On the Atlantic Coast of North America, predominantly a loop migration pattern described from locations of loons marked with satellite transmitters (n = 46; 39). In spring, movements along U.S. Atlantic coast to stopover sites at Narragansett Bay, Long Island Sound, Cape Cod Bay and Nantucket Sound and Shoals. Continued movement north through the Gulf of Maine and Bay of Fundy to stopover in the Gulf of St. Lawrence and St. Lawrence River for up to one month and then dispersing to breeding locations. Some use of an alternative spring migration route that passes inland from the mid-Atlantic wintering grounds to the lower Great Lakes where migration paused until birds moved to breeding sites. Different route often taken during fall migration. Loons moved from breeding sites to Hudson Bay or Ungava Bay, both likely sites of remigial molt. Movement resumed southward through Hudson Bay to James Bay. Loons in Ungava Bay fly over Quebec or move south along Canadian coast of Labrador Sea to St. Lawrence River and Gulf of St. Lawrence. Return to mid-Atlantic wintering grounds either overland from the Lower Great Lakes to Delaware Bay or along coast south from Gulf of St. Lawrence.
Of 33 individuals marked with satellite transmitters while wintering in the North Sea (155) and tracked during spring migration to potential breeding sites, 24 (73.5%) migrated to Russia, 4 to Norway, 2 to Greenland, and 2 to Svalbard. Sites in Russia included Siberia (Yamal, Gydan, Kanin Peninsula, and the western Siberian Plain) and western Russia (Kola Peninsula, Kanin Peninsula, Pechora Sea, and Novaya Zemlya). Migration routes typically followed coastlines and minimized overland flights. Routes to sites in Siberia followed the Baltic Sea to the White Sea or Barents Sea; 1 individual followed the coast of Norway. Two routes to western Russia: one to the Baltic Sea and overland through Denmark and Schleswig Holstein, and the other along the coasts of Denmark and Schleswig Holstein. Routes to Greenland were via Norway to east Greenland and via Scotland and Iceland to west Greenland. Three broadly dispersed sites in Norway were reached either by following the southern coast or moving north through Oslofjord and overland through Norway. Two routes to Svalbard were documented, one direct and the other indirect via a staging site 200 km east of North Cape. The maximum spring migration distance, assuming a straight-line flight path, was 5,000 km to Greenland and the minimum was 850 km to Norway. The average straight-line migration distance to northern Russia was 4,000 km (maximum 4,980 km to the Taimyr Peninsula; minimum 2,200 km to the Kola Peninsula). Fall migrations followed similar routes as documented during the spring. Likely sites of remigial molt included Baltic Sea (n = 17), North Sea (n = 1), and Scotland (n = 1); Baltic Sea and North Sea molting areas were confirmed by stable-isotope analysis of neck contour feather samples (155).
Flies in flocks of ≤ 15 (184), low (5–70 m) over coastal waters along Atlantic Coast at 50–70 km/h, higher (1,000–1,700 m) and faster inland (179). Along Pacific Coast, often flies just behind breaking waves (135). Hundreds in Delaware Bay move together with tide along rips to feed on fish and crabs (Callinectes sp.), then fly up-current to drift back again (179). Usually migrates in loose aggregations; rare observations of overland V-formations (185).
Control and Physiology of Migration
Hormonal regulation and orientation methods unknown.