Migration

All North American populations are migratory, wintering mainly in South America or w. Central America. Even birds breeding in Netherlands Lesser Antilles depart for the northern winter (Voous 1957). One-year-olds largely remain on or near wintering grounds throughout breeding season, but most birds ≥2 yr old migrate to breeding areas.

Austin (1953), Houston (1972, 2000), Haymes and Blokpoel (1978), Blokpoel et al. (1987, 1996) and Hays et al. (1997) analyzed 3,951 recoveries and 321 sightings of Common Terns banded in North America. The recoveries fall into 3 groups defined by areas of banding (Austin 1953).

Atlantic Unit birds (banded on Atlantic Coast from Nova Scotia to Virginia) recovered largely east of 75°W: on Atlantic Coast of U.S. north of Virginia, Bahamas, West Indies, and South America from Colombia east and south to n. Argentina.

Central Unit birds (banded in St. Lawrence River, Great Lakes, or Minnesota) recovered largely west of 75°W: on Atlantic Coast of U.S. from Virginia south, around Gulf of Mexico, on both coasts of Central America, and on west coast of South America south to s. Peru. Birds banded in Lake Champlain and St. Lawrence River show mixed pattern: 4 recovered east and 9° west of 75°W (Cuthbert and Timmerman 2001). Common Terns banded in Bermuda recovered in Brazil (1) and Amazonian Peru (2; D. B. Wingate).

Northwest Unit birds (banded in Alberta and Saskatchewan) winter exclusively on Pacific coast from central Mexico south, farther north than those from Central Unit (Houston 2000). Among 3 distant recoveries of birds banded in Manitoba, 1 was in French Guiana and 2 on Pacific coast, suggesting pattern mixed between those of Central and Northwest Units (Houston 2000).

Four Common Terns banded in North America recovered in e. Atlantic: one near the Azores, one each in France, Ivory Coast, and Togo (Nisbet and Safina 1996). Birds banded in Ontario and Michigan recovered in Hawaiian Is. (Clapp et al. 1983a); one banded in Saskatchewan recovered in the Cook Is. (Houston 1972). One banded in Finland recovered in Trinidad (ffrench 1991); several banded in the Azores recovered in e. Brazil, and vice versa (Hays et al. 1999), suggesting regular transatlantic migration.

No direct evidence of migration routes. Atlantic Unit birds disperse throughout breeding area Jul–Aug (Austin 1953, Nisbet 1976), concentrating at staging sites from New Jersey to s. Maine, with flocks of up to 10,000 reported around Cape Cod, MA, 13 Aug–24 Sep (Veit and Petersen 1993, Trull et al. 1999). Probably migrate directly south across w. North Atlantic from mid-Aug to mid-Oct, reaching West Indies from Hispaniola eastwards; few recoveries on Atlantic Coast south of Virginia (Austin 1953). Most recoveries in n. West Indies Sep–Oct, s. West Indies and Guyana Oct–Nov, e. and s. Brazil Dec–Apr (Austin 1953, Hays et al. 1997). Most birds recovered in s. Brazil and n. Argentina were >2 yr old; first-winter birds largely north of 10°S (Hays et al. 1997). Major concentrations reported in Dec–Apr at Mangue Seco and Lagoa do Peiche, Brazil, and Punta Rasa, Argentina (Harrington et al. 1986; Hays et al. 1997, 1999). Adults stay in these concentrations into Apr or early May, so spring migration must be very rapid. Birds banded at Lagoa do Peiche (31°22´S) and Punta Rasa (36°15´S) were trapped on nests at Great Gull I., NY (41°12´N), within 40 d and must have flown the entire distance (7,000–8,000 km) within 22 and 28 d, respectively (Hays et al. 1997). Rarely reported on spring migration, but at Salinas, n. Brazil, flock of 8,000 stayed for a few hours on 12 Apr 1997 (C. D. T. Minton). Arrives in breeding areas from 25 Apr to 13 May, sometimes in large flocks, occasionally staging on outer beaches in New York and Massachusetts (Palmer 1941, Veit and Petersen 1993, Levine 1998).

One-year-olds rare in breeding areas; recoveries not reported precisely, but at least some were in wintering areas (Hays et al. 1997). Many 2-yr-olds migrate north, arriving at breeding colonies in mid- to late Jun, some breed; 3-yr-olds arrive at breeding colonies in late May, many breed (Austin and Austin 1956). Many older birds reported in winter quarters May–Jul (Austin 1953, Hays et al. 1997), but ages and recovery dates not reported precisely.

Central Unit birds disperse throughout breeding area Jul–Aug (Blokpoel et al. 1987), concentrating in s. Great Lakes in early Sep, when staging flocks of up to 10,000 reported (Mumford and Keller 1984, Peterjohn 1989, Granlund et al. 1994, Levine 1998). Many or most migrate overland to Atlantic Coast from New York south (Austin 1953, Haymes and Blokpoel 1978), thence to wintering areas in Florida, Central and South America. Many also migrate directly south–southwest from Great Lakes to Gulf Coast, as shown by recoveries on Gulf Coast west of Florida and inland in Texas and Oklahoma (Austin 1953, Haymes and Blokpoel 1978), and sightings in all interior states. Staging flocks of up to 5,000–10,000 birds reported on Padre I., TX, in Sep–Oct (Clapp et al. 1983b). In contrast to Atlantic birds, Central Unit birds appear to migrate rapidly to winter quarters: distribution of recoveries in Central and South America similar in Oct–Nov to that in later months (Haymes and Blokpoel 1978). However, substantial numbers linger in Great Lakes until mid-Oct, some into Nov (Mumford and Keller 1984, Peterjohn 1989, Robbins 1991, Levine 1998). Adults recovered Dec–Mar were almost entirely south of 10°N, while first-winter birds were mainly in Florida, Gulf of Mexico, and w. Caribbean (Haymes and Blokpoel 1978).

Spring migration poorly documented south of breeding area, but staging flocks seen 3–16 May in Texas and Alabama (Clapp et al. 1983b). Probably migrate directly over land from Gulf of Mexico to Great Lakes (Austin 1953); only 1 recovery on s. Atlantic Coast (Haymes and Blokpoel 1978). Migrants arrive in lower Great Lakes in mid-Apr (Levine 1998). In Michigan, Illinois, and Wisconsin, however, main arrival early May (Mumford and Keller 1984, Robbins 1991). Large numbers stage in Lake Michigan in mid-May (Mumford and Keller 1984, Robbins 1991), probably on way to breeding sites north or west of Great Lakes.

Most recoveries of 1-yr-olds were in winter quarters, including Florida and Gulf Coast (Haymes and Blokpoel 1978). All recoveries of 2-yr-olds during breeding season were from Great Lakes, most in Jun–Jul but a few in May (Haymes and Blokpoel 1978).

Northwest Unit birds migrate across mountains to and from Pacific Coast (Houston 2000). Start to arrive in coastal British Columbia and California mid- to late Jul, large numbers from late Aug to mid-Oct in both areas, departing by early Nov. Peak numbers in spring from mid-Apr to mid-May in California, about 2 wk later in British Columbia (Campbell et al. 1990, Small 1994). Arrive on breeding lakes in Alberta in late Apr and early May, departing by mid-Sep (Weseloh 1973, Semenchuk 1992).

Migrations of w. Palaearctic birds reported in detail by Glutz von Blotzheim and Bauer (1982) and Cramp (1985). Information on S. h. longipennis summarized by Higgins and Davies (1996).

No studies reported in North America. In Massachusetts, flocks of thousands seen arriving at breeding sites in May; one flock of at least 10,000 birds circled high into the air at dusk and departed southwest over ocean on 21 Sep (Veit and Petersen 1993). Alerstam (1985) used radar to track terns (Common and/or Arctic) crossing s. Sweden in late Jul. Small flocks took off in evening, ascended at rates of about 1.2 m/s to heights of 1,000–3,000 m, flying at airspeeds of about 10 m/s when ascending and 12–15 m/s (40–55 km/h) in level flight. Some flocks circled in thermals, alternately flapping and soaring. These observations suggest terns start migratory flights in evening and fly at high altitudes during night, consistent with paucity of records of terns traveling by day.

No studies in North America, except that Griffin (1943) and Griffin and Goldsmith (1955) used Common Terns in studies of homing. Peters (1933) reported on pre-migratory fattening in autumn in Germany. Alerstam (1985) discussed energetics.