Distribution

Breeding Range

In North America, breeds in widely scattered localities in 6 regions:

(1) Pacific Coast, at Neragon I., Bering Sea, near Cape Romanzof, AK, next nearest probable breeding site >1,100 km southeast at Copper River delta near Cordova, AK; moving south, large gap until sw. British Columbia on Fraser River delta, locally in coastal and e. Washington, Oregon, w. Nevada, and California, south to Laguna San Ignacio, Baja California Sur, and coast of Sinaloa, Mexico, at Isla Laricion (Jehl 1986, Am. Ornithol. Union 1983, Campbell et al. 1990, Gibson and Kessel 1992, Palacios and Alfaro 1992, Massey and Palacios 1994, Howell and Webb 1995, McCaffery et al. 1997, Parkin 1998, C. Collins pers. comm.).

(2) Central Canada, in s. Northwest Territories at Great Slave Lake; ne. Alberta at Egg I., Lake Athabasca, and a few sites in s. Alberta; central Saskatchewan at Churchill, Dore, and Last Mountain Lakes; and s. and s.-central Manitoba primarily at Lakes Winnipeg and Winnipegosis (Vermeer 1970, Weseloh and Cocks 1979, Semenchuk 1992, Bennett 1995, Sirois et al. 1995, Sherrington 1996, Smith 1996, B. Koonz pers. comm.).

(3) W.-central interior U.S., south across s. Idaho along or near Snake River; in nw. Wyoming at Yellowstone Lake, west-central at Ocean Lake, central at Amoco Soda Lake, and southeast at Bamforth Lake; and in n. Utah at Great Salt Lake and Utah Lake (Hayward 1935, Am. Ornithol. Union 1983, K. Ryan pers. comm., A. Cerovski pers. comm., D. Paul pers. comm., C. Trost pers. comm.).

(4) Gulf Coast, from coastal Texas to Tampa Bay, FL (Rodgers et al. 1996, Pranty 1997, M. Lange unpubl., G. Lester pers. comm., B. Vermillion pers. comm., J. Jackson pers. comm.).

(5) Atlantic Coast, in Labrador at Lake Melville; Newfoundland at Bellevue and Ladle Cove Is.; se. Quebec along lower North Shore (Fog I., Natashquam) and possibly Magdalen Is., moving south large gap until N. Carolina coast on islands near Oregon Inlet, a few pairs along Virginia’s barrier islands, and formerly in Florida at Merritt I. National Wildlife Refuge (Lock 1983, Godfrey 1986, Williams et al. 1990, Parnell et al. 1995, Chapeldaine 1996, Rodgers et al. 1996, D. Ballam pers. comm.).

(6) Great Lakes, from n. Lake Michigan (Wisconsin and Michigan), n. Lake Huron including North Channel and Georgian Bay (Ontario) south to Saginaw Bay (MI), Lake Ontario (Ontario and New York), and Thousand Is. group in upper St. Lawrence River (Ontario). In addition, in James Bay, Akimiski I. (Ludwig 1965, Cuthbert 1981, Godfrey 1986, Weseloh and Blokpoel 1993, Blokpoel and Tessier 1996, 1997).

Isolated instances of breeding in n.-central Minnesota (Warner and Beimborn 1969, Budde et al. 1997), central North Dakota (Herman et al. 1978), and New Jersey (Burger and Gochfeld 1984-1985).

Winter Range

Winters along Pacific Coast from s. California (Santa Barbara Co.) south to Guatemala (including entire Gulf of California), but apparently unrecorded in El Salvador (Small 1994, Howell and Webb 1995, Christmas Bird Count [CBC] data). Small numbers also winter locally along coast of n. California (CBC data) and around Golfo de Nicoya of Costa Rica (Stiles and Skutch 1989). Winters along Atlantic and Gulf Coasts from southernmost N. Carolina (New Hanover Co.) south around Florida Peninsula (but absent from coast of Florida Panhandle except Gulf and Franklin Cos.), west to s. Texas, and south along coast of Mexico to at least n. Honduras. Within this area, winter range extends inland to include most of Florida Peninsula (decreasing toward northwest), coastal plain of s. Texas, and Atlantic slope of Mexico from Tamaulipas and e. Nuevo León south to Tabasco (Stevenson and Anderson 1994, Howell and Webb 1995, CBC data). In Mexico, also winters locally (rare to uncommon) in Central Volcanic Belt from Jalisco and Colima eastward (Howell and Webb 1995). Also winters locally (rare) in w. West Indies, including s. Bahamas, Cuba, Hispaniola, and Jamaica; and Barbados in e. West Indies (Raffaele et al. 1998); along Atlantic coast of Panama, particularly in Panama Canal area (Ridgely and Gwynne 1989); and Atlantic coast of South America, where species has been recorded from n. Colombia (Hilty and Brown 1986) and w. Venezuela (at least to Lake Maracaibo; Meyer de Schauensee and Phelps 1978). Occasionally recorded in winter from N. Carolina north along Atlantic Coast (e.g., Sibley 1993); very rare winter resident on Puerto Rico and Cayman Is.; accidental elsewhere in West Indies (Raffaele 1998). Highest early-winter abundances in U.S. are on eastern coast of Florida and Gulf Coast of Texas (Root 1988).

Breeding Range

Distribution of Old World breeding populations is fragmented. In Eurasia, Baltic Sea on coasts of Sweden, Finland, and Estonia; from northern coasts of Black Sea and Sea of Azov across nw. Iran, s. Russia, and Caspian and Aral Seas to n. Mongolia, s. Siberia, and coastal e. China; from Red Sea and Persian Gulf east to Pakistan and Sri Lanka. In sw. Pacific, locally on islands around coast of Australia, North and South Is. of New Zealand, and Tasmania. In nw. Africa, mostly coastal localities, including Gulf of Suez; Tunisia; off n. Mauretania to Guinea; and Nigeria. In s. Africa, coastally from Swakopmund, Namibia, to Lake St. Lucia, South Africa; scattered inland localities in Botswana and South Africa; and in Africa’s interior at Lake Rudolph in Kenya (Clapp et al. 1983, Sibley and Monroe 1990, Cooper et al. 1992).

Winter Range

From Kilpi and Saurola 1984 and Cramp 1985 . Most individuals that breed in Baltic and Black Seas winter in upper Niger inundation zone in Mali and Gulf of Guinea; a few winter in Mediterranean and upper Nile, Sudan. Birds from Caspian, Aral, and Kazakhstan regions winter in Persian Gulf and on coasts of Iran, Pakistan, India, and Bangladesh. Breeders from Mauretania probably winter on coast; birds that winter on Africa’s east coast also are local, or possibly Caspian Sea populations (Kilpi and Saurola 1984). South African birds winter along s. African coastline and at coastal water bodies from Namibia-Angola border to Zambesi Estuary in central Mozambique (Cooper et al. 1992).

North American breeding range has expanded since beginning of twentieth century. In early 1900s, western birds gradually shifted nesting from interior freshwater sites to human-created habitats in coastal areas. By 1930, no large colonies existed away from Pacific Coast (Gill and Mewaldt 1983). By 1970s, regular summer visitor to southern coast of British Columbia; breeding documented there in 1984 (Campbell et al. 1990). Added to list of Alaska birds in 1981; by 1989, suspected to breed in se. Alaska (Gibson and Kessel 1992); in 1996, breeding documented on west-coastal Alaska (McCaffery et al. 1997). Range also expanded in se. U.S.; first documented nestings in Florida, Alabama, and N. Carolina in 1960s and 1970s (Woolfenden and Meyerriecks 1963, Parnell and Soots 1976, Portnoy 1977). In central Canada, range expanded southward; nesting documented in s. Alberta in late 1980s and early 1990s (Semenchuk 1992, Bennett 1995, M. Preston pers. comm.). In many parts of range, populations have increased, apparently largely because of human alterations in habitat—e.g., construction of levees in association with salt evaporation ponds and creation of dredge-spoil islands (Gill and Mewaldt 1983). Effective federal legislation, public ownership, protection of many colony sites, and growing public concern have also contributed to increases (see Conservation and management, below).

No substantial reduction in breeding range, although numbers have sharply declined along some parts of the Atlantic coast (see Demography and populations: population status, below).

Outside North America, range has decreased. In Denmark, West Germany, East Germany, Romania, and Tunisia, where species formerly bred fairly reg-ularly, it is now occasional or extinct (Cramp 1985).

No records. Excavations on southwestern shores of Buena Vista Lake, Kern Co., CA, in 1933–1934 exposed skeletal remains of a Caspian Tern not >500 yr old (DeMay 1942).