Distribution

Breeding Range

Widely distributed in North America, but not beyond (Fig. 1); currently expanding, but mostly within historical range (Hatch 1995). Breeding cormorants are most numerous in the outer parts of this range. The 5 main zones are (1) Alaska, (2) Pacific Coast from s. British Columbia to n. Mexico, (3) Canadian and U.S. interior, (4) Atlantic Coast from Newfoundland to New York, and (5) Florida and the w. Caribbean. For (1) and (2), see Carter et al. 1995 . Recent expansion has blurred boundaries for (3), (4), and (5).

Alaskan population breeds at Nunivak I. (60°N) and se. Bering Sea and from e. Aleutian Is. to se. coast, including Kodiak I. (Carter el al. 1995, USFWS 1999), and inland to Lake Louise, AK. First nest in Yukon Territory confirmed in 1998 at Lake Laberge (Bain and Shanahan 1998).

Pacific population breeds between s. British Columbia and Sinaloa, Mexico. In these coastal areas, Double-crested Cormorant is generally outnumbered by other cormorants. Smaller numbers nest inland, without other cormorants, except in Mexico where the Neotropic Cormorant occurs. Breeds in Strait of Georgia in s. British Columbia and n. Washington (Campbell et al. 1990, Smith et al. 1997). In Washington and Oregon, most breeders are coastal, with small numbers inland, occasionally along lower Columbia River and n. Willamette River. East of Cascades, colonies are widely scattered and locations shift in response to fluctuating water conditions, but most occur in Klamath, Lake, and Harney Cos., OR, and Grant Co., WA (Gilligan et al. 1994, Smith et al. 1997).

In California, most individuals nest coastally, especially from Cape Mendocino northward, and in lakes and marshes of Siskiyou, Modoc, and Lassen Cos.; small numbers in San Francisco Bay, Central Valley, and lower Colorado River; declining numbers on Salton Sea; and very locally elsewhere (Small 1994).

In Mexico, breeds along Pacific coast of Baja California, on islands in Gulf of California, and locally inland in Durango and se. Sonora, and on coast of central Sonora (Howell and Webb 1995, Russell and Monson 1998). Records from Sinaloa date from 1970s (Carter et al. 1995).

In the interior of the continent, northern limits of breeding may be determined by short season and distribution of productive lakes: from the southern boreal forest in n. Alberta, Saskatchewan, and Manitoba, through central Ontario (primarily along Great Lakes); James Bay, where a single colony reported from Rupert Bay (Tymstra 1997) and sw. Quebec, south to central Utah, central Colorado, w.-central Nebraska, se. South Dakota, w.-central Minnesota, ne. Iowa, central Wisconsin, and n. Lower Peninsula of Michigan. Range extends west to sw. Idaho and east along Great Lakes to lower St. Lawrence River. Also breeds locally elsewhere in s. Ontario, in sw. Quebec (Gauthier and Aubrey 1996), central Kansas (Barton Co.; Kansas Breeding Bird Atlas unpubl.), s. New Mexico (lower Rio Grande and Pecos River valleys; Hubbard 1978), and irregularly elsewhere within central North American interior.

On Atlantic Coast, breeds almost entirely at coast from s. Newfoundland, north shore of Gulf and the estuary of St. Lawrence, Anticosti I., Magdalen Is., and south to New York City. Now expanding south into mid-Atlantic states (see Historical changes, below). Inland nesting now well established on Lake Champlain (Vermont/New York), and by small numbers elsewhere—in Quebec, Maine, Connecticut, Pennsylvania, Virginia, and the Carolinas.

In Southeast, resident throughout Florida except panhandle (Stevenson and Anderson 1994, Hatch 1995). Generally absent or rare as breeder from adjacent Georgia, Alabama, Mississippi, and Louisiana. Scattered residents breed in Cuba, where colonies are reported in some small keys off northern coast, from Bahía de Cadiz to Cayo Santa María; also in s. Havana province and Golfo de Guacanayabo (O. Garrido and A. Kirkconnell unpubl.). In n. Bahamas, known as uncommon resident, nesting confirmed on San Salvador, Long I., and Eleuthera (Connor and Loftin 1985, Watson et al. 1991). Also nests on coast of n. Yucatán Peninsula (Mexico) and n. Belize (Howell and Webb 1995, Raffaele et al. 1998).

Nonbreeding Summer Range

Found mostly within limits of its wide breeding range, but occurs farther from breeding colonies, even to elevations of >2,000 m, as at Crater Lake, OR (Gilligan et al. 1994). Uncommon in Queen Charlotte Is., British Columbia. Some remain in wintering areas (e.g., ne. Mexico [Howell and Webb 1995], and Florida, where indistinguishable from residents, and Mississippi). In late summer, likely to disperse beyond breeding range—e.g., to Great Slave Lake, Northwest Territories.

Winter Range

On Pacific Coast, including Alaska, chiefly resident; there is some dispersal northward, but more southward, especially from inland, as far as Sinaloa, Mexico. In British Columbia, birds wintering north of breeding areas likely include migrants from Alaska. Also winters inland along Columbia River of Washington and Oregon, throughout the near coastal counties of Oregon and California, throughout Central Valley of California, and along lower Colorado River (Christmas Bird Count [CBC] data). These patterns are not based on marked individuals.

Individuals breeding in interior of continent and on Atlantic Coast are strongly migratory, most wintering coastally from N. Carolina to w. Gulf of Mexico, with smaller numbers north to New Hampshire (Root 1988, Sauer et al. 1996, Davenport 1998, CBC records). Also winters along Gulf Coast of Mexico from Tamaulipas south to the Yucatán Peninsula and Belize. Banded birds recovered from as far as Quintana Roo, Mexico. Numerous band recoveries show that mixing occurs of birds from across wide breeding range east of Rocky Mtns. (Dolbeer 1991, Hatch 1995), as well as overlap with residents.

North American birds also winter in n. Bahamas, with occasional sightings in Puerto Rico and n. Lesser Antilles (Raffaele et al. 1998), and south to Cuba. Banding recoveries include 12 in Cuba (banded S. Dakota–Quebec), 1 in n. Bahamas. On Bermuda, small numbers have wintered since about 1980 (Amos 1991).

Significant numbers occur in winter at inland lakes, rivers, and impoundments; regularly winters inland from Atlantic Coast along major rivers to se. Pennsylvania, central Maryland, and throughout lower coastal plains of Virginia and the Carolinas. Also winters inland from Gulf Coast (especially along the Mississippi and other rivers) north to central Georgia, n. Tennessee, sw. Indiana, s. Illinois, n. Arkansas, e. Kansas, eastern half of Oklahoma, Texas (except for panhandle); in ne. Mexico in Nuevo León, Tamaulipas, and n. Veracruz; and along Rio Grande and Pecos Rivers of s. New Mexico and w. and s. Texas (CBC data, Howell and Webb 1995). To the north, small numbers are increasingly observed on CBCs in coastal New England, the Maritime Provinces, the Great Lakes, and the prairies.

Other populations breeding in Florida, Mexico, Cuba, and the Bahamas are resident. In southern areas, influx of migrants is added to residents, but no information is available on possible differences in habitat use. For possible sex differences in wintering areas, see Habitat, below.

Vagrants reported from the Azores in 1991, England in 1989 (BOURC 1993).

From Hatch 1995 . Present as breeders in New England in seventeenth century, also at Lake of the Woods, Ontario, in eighteenth century (Peck and James 1983), but full extent of range at that time unknown. Numbers and range greatly reduced by early twentieth century, probably from widespread direct persecution and some loss of inland habitat from agricultural clearances (see Conservation and management, below). Extirpated from New England, Vancouver I., and w. Aleutians, and probably withdrew from many areas. Subsequent great increases (and decreases) in numbers reflect several human-induced changes (see Demography and populations, below) and have been mostly within the historical range, except possibly for the Great Lakes, where nesting was first recorded in Lake Superior in 1913 and subsequently spread eastward to the remaining 4 lakes (Weseloh et al. 1995). This spread could have represented recolonization of areas from which breeding birds were extirpated before the earliest records. For British Columbia, first breeding record was in early 1920s, but archaeological evidence suggests this was a return and not a range extension. Expansion into many previously unoccupied arid areas has been enabled by construction of dams—e.g., into e. Colorado, where first nested in 1931 (Andrews and Righter 1992); Wyoming, where first nested in 1928 and 73% were nesting on reservoirs in 1986 (Findholt 1988); and S. Carolina (Post 1988).

Returned to Massachusetts by 1940, and since 1970 has extended its breeding range along coast to New York City and locally south to merge with the population that is resident in Florida and the Carolinas. Mid-Atlantic states are now (1997) a region of local expansion; first nestings in Virginia in 1978, Maryland in 1990, Pennsylvania in 1996 (Blem et al. 1980, McConaughy 1996, Robbins 1996). From Prince Edward I., first record of nesting was 1941, but no information about possible earlier occurrences. On Lake Champlain (Vermont/New York), first recorded nesting in 1982; origins of these birds unknown. In Alaska, extended range north to Nunivak I. by 1991 (Tobish and Isleib 1992), but has not recolonized the w. Aleutians.

In the South, has not yet returned to areas where colony sites were cleared during agricultural development (Jackson and Jackson 1995), but many winter and first nesting reported in Mississippi in 1998 (Reinhold et al. 1999). Nesting in Yucatán (Mexico) or nearby not reported by Palmer (1962), but was possibly overlooked because this species is sympatric there with the similar Neotropic Cormorant. The scattered occurrence of early-winter stragglers, increasingly seen on CBCs throughout much of the interior, is unlikely to represent a biologically significant extension of the wintering range, although substantial numbers now occur in vicinity of aquacultural ventures in Mississippi and other southern states.

Cormorants are quite numerous in the fossil record, extending back to the Oligocene. The present species is represented by Pleistocene and prehistoric records, notably from coastal sites, widely distributed within the present breeding range (Brodkorb 1963, Hatch 1995). The only long archaeological record is from Amchitka I. in the Aleutians (from 2,650 yr ; Siegel-Causey et al. 1991).