Welcome to the Birds of North America Online!
Welcome to BNA Online, the leading source of life history information for North American breeding birds. This free, courtesy preview is just the first of 14 articles that provide detailed life history information including Distribution, Migration, Habitat, Food Habits, Sounds, Behavior and Breeding. Written by acknowledged experts on each species, there is also a comprehensive bibliography of published research on the species.
A subscription is needed to access the remaining articles for this and any other species. Subscription rates start as low as $5 USD for 30 days of complete access to the resource. To subscribe, please visit the Cornell Lab of Ornithology E-Store.
If you are already a current subscriber, you will need to sign in with your login information to access BNA normally.
Subscriptions are available for as little as $5 for 30 days of full access! If you would like to subscribe to BNA Online, just visit the Cornell Lab of Ornithology E-Store.
Nature Of Migration In The Species
Variable; birds nesting in the interior and on the Atlantic Coast (P. a. auritus) are highly migratory; all age groups migrate. Immature birds arrive later in spring but are not known to occupy different ranges. In other areas, mostly resident within breeding range, and very little is known of migratory habits. In Florida and the Caribbean, P. a. floridanus is reported to be resident, but withdraws from the Carolinas in winter (Bent 1922). Its breeding range overlaps with migration and wintering areas of P. a. auritus, from which it is indistinguishable in the field.
In the Bahamas, P. a. heuretus is probably resident (Watson et al. 1991). The more northerly populations of P. a. cincinatus (in Alaska) may migrate south to s. British Columbia, especially the outer coast (Campbell et al. 1990, Johnsgard 1993) and Washington, but specific data are lacking. In Mexico and California, coastal and southern areas receive an influx of birds in fall, probably P. a. albociliatus from inland or farther north. Birds banded in British Columbia are encountered south to s. California.
A change in wintering areas (and migration routes) is suggested by recoveries of cormorants banded in S. Dakota; from Louisiana in 1930 to Texas and Mexico in 1960s (Drewlen and Fredrickson 1969). King et al. (2010) indicated a potential shift inland for wintering cormorants in the Southeast due to the expansion of catfish aquaculture in the region.
Timing And Routes Of Migration
Some birds leave the Gulf of Mexico as early as Feb. They follow the Atlantic coastline or river systems, as well as going overland. Earliest individuals reach Oklahoma and Virginia by 4–5 Mar (Sutton 1967, Kain 1987); Massachusetts, s. Great Lakes, Minnesota, S. Dakota, and s. Idaho by late Mar-early Apr; upper Great Lakes by early to mid-Apr; coastal Maine, Alberta, and Saskatchewan by mid- to late Apr. First adults arrive at colonies in e. Lake Ontario when ice breakup is well advanced but large areas of pack ice are usually still present (DVW). Similarly, first arrivals at North Channel (Lake Huron) may be confined to river or creek mouths that form the only open water (S. Elliott pers. comm.). Peak spring migrations occur 3–4 wk later, in Missouri in third week of Apr (Robbins and Easterla 1992), in Massachusetts in late Apr.
Cormorants marked with satellite telemetry on their wintering grounds in Mississippi departed for spring migration between 26 Mar and 12 May, with adult cormorants departing earlier for spring migration than immatures (King et al. 2012a). Mean duration of migration was 12 d, with marked cormorants traveling an average of 70 km/d (King et al. 2012a).
Records of migrants in large numbers en route are rarely published, but a very large passage was reported on 24 Apr 1926, when “100,000–1,000,000” cormorants passed La Crosse, WI, flying up the Mississippi River (Robbins 1991). From banding recoveries, Dolbeer (1991) concluded that first-year birds return north about a month later than older birds.
On the Pacific Coast, migration is poorly known because some individuals are resident year-round. Migrants leave Oregon in Mar (Gilligan et al. 1994). In British Columbia, migration period is mid-Mar–late May, with heaviest movements late Apr–early May (Campbell et al. 1990). In interior Oregon, migrants arrive Feb–Mar. In California, arrive at Farallon Is. early Mar–mid-Apr (Ainley and Boekelheide 1990).
Autumn migration is essentially the reverse of spring migration, but movements are well under way before open water becomes limiting. Earliest autumn migrants appear to reach wintering grounds faster than they reached breeding grounds in spring, although overall timing is more protracted. The average departure date for fall migration of satellite-marked cormorants from various locations in their breeding range was 1 Oct (range, 17 Aug to 25 Oct, n = 8; see King et al. 2012). Females may have an earlier mean departure date (12 Sep [n = 10]) than males (7 Oct [n = 16]; see Scherr et al. 2010).
Cormorants marked from a colony managed for reduction in numbers by egg-oiling had a mean departure date of 6 Sep (range 12 Jul to 29 Oct, n = 24; see Dorr et al. 2012d), suggesting that egg-oiling induced nest failure may result in slightly earlier migration. Several juveniles banded in Michigan have been recovered on the Mississippi River from s. Minnesota to s. Missouri by late Jul (J. Ludwig unpubl.). More usually, migration is evident on Canadian prairies by mid- to late Aug; by then first migrants are on the upper Mississippi River (Kirsch 1997) and in Ohio, Massachusetts, Virginia, and even Texas (Oberholser 1974).
By September, migration is well under way throughout the range. From Lake Champlain (Vermont/New York), all individuals depart within a few days in late September (D. Capen pers. comm.). Several areas report peak numbers of transients in Oct (Massachusetts and Rhode Island: first half; Minnesota: third week). Very few descriptions available of what must be large movements both down the Mississippi River/Flyway and out of the Great Lakes: Two reports from 1940s describe 9,500 and 15,000 birds, respectively, passing Havana, IL, on single days in early Oct (Mills et al. 1966). Near Rochester, NY, hundreds are seen each year flying westward along the southern shore of Lake Ontario (B. Ewald unpubl.).
Most banded migrants are recovered in Oct and Nov (Dolbeer 1991). Mean duration of fall migration of satellite-marked cormorants from a colony in e. Lake Ontario was 34 d (range 2-110 d, n = 19; see Dorr et al. 2012d). Mean duration of fall migration of satellite-marked cormorants from a colony in n. Lake Huron was 41 d (range 6-87 d; see Scherr et al. 2010). The mean migration distance that birds traveled from n. Lake Huron to their winter location was 2,060 km (Scherr et al. 2010). The greatest daily movement was 343 km/d by a female; however, males and females did not differ (Scherr et al. 2010).
Patterns of coastal migration in New England, described by Nisbet and Baird (1959), continue with much greater numbers in 1990s (JJH). Flocks are generally observed along the coast, except where they fly overland to bypass Cape Ann, MA, and again for Cape Cod. Small flocks appear in mid-Aug, but most migration has been observed 25 Sep–17 Oct. Individuals arrive in wintering areas Sep–Nov. Some fly across open ocean (species now winters regularly in Bermuda), but is rarely seen during cruises in search of pelagic seabirds.
There is evidence of a migratory divide and migratory connectivity for the Atlantic and Mississippi flyways (Scherr et al. 2010, Dorr et al. 2012d, Guillaumet et al. 2012). Cormorants breeding west of central Lake Erie tend to migrate west of the Appalachians and congregate in the lower Mississippi valley; eastern breeding birds migrate east of the Appalachians and winter primarily in the Florida wetlands and as far north as the Carolinas (Guillaumet et al. 2012). Favorable wetlands-rich habitats in Florida and the Mississippi alluvial valley and the Appalachian Mountains may influence this divide (Guillaumet et al. 2012). However, cormorants display a great deal of individual variation in migratory routes, with individuals using different migratory routes for spring and fall in the same year (Dolbeer 1991, Guillaumet et al. 2012).
The aquaculture regions of the Southeast have also been suggested as a favorable habitat for wintering cormorants. Large numbers of cormorants use aquaculture-producing areas of the southeast during winter (Glahn et al. 2000, Dorr et al. 2012a). However, Scherr et al. (2010) found few satellite-marked cormorants from n. Lake Huron using aquaculture-producing areas.
Several important fall staging areas have been identified from satellite telemetry in w. Lake Erie, the Eastern Basin of Lake Ontario, Lake Champlain, Chesapeake Bay, and Albemarle and Pamlico sounds (Scherr et al. 2010, Dorr et al. 2012d, Guillaumet et al. 2012). These areas are likely important stopover foraging habitats for migrating cormorants. Potential staging areas of cormorants breeding further west in the Great Lakes and Prairie Provinces are not well documented.
On the Pacific Coast, migrants are evident in British Columbia from late Aug to early Nov; influx into inner coastal waters peaks in early Sep (Campbell et al. 1990). In coastal Oregon, migrants arrive Jul–Aug; east of the Cascade Mtns., the last migrants depart Oct–Nov (Gilligan et al. 1994). Depart from the Farallon Is., CA, after last young fledge in late Sep (Ainley and Boekelheide 1990). Cormorants marked with satellite tags from a colony at the mouth of the Columbia River, OR, dispersed from the Columbia River estuary 1 Jul to 1 Dec (mean Aug 27th). All tagged cormorants had left the region by mid-Dec, with the exception of a small number of resident birds; post-breeding cormorants dispersed up to 1,805 km from the mouth of the Columbia River estuary; more than half of satellite-marked cormorants wintered north as well as south of the colony (Courtot et al. 2012). Both satellite tags and banding data indicate that cormorants on the Pacific Coast infrequently travel east of the Cascade-Sierra Nevada Range (Clark et al. 2006, Adkins and Roby 2010, Courtot et al. 2012).
Most inland records of migratory flights are of small flocks, <50–100. Along coasts, near-shore flocks may be large (in the thousands). Over water, migrants usually fly low, in wavering lines or irregular V-formations; over land, fly as high as 1,000 m.
An autumn departure from Presqu’Ile Bay, Lake Ontario, was described as follows: “At mid-morning a flock of approximately a thousand cormorants began to take flight from a large protected bay and spiraled upward to a height of several hundred feet. They circled and then flew off to the south, as if to fly across the lake. Several minutes later, however, they returned, resumed their high altitude circling (much the way passerines do during migration before crossing a large body of water) then departed a second time to the south and did not return” (R. D. McRae pers. comm.).
Little information available on daily duration; flights start soon after dawn and continue all day (Nisbet and Baird 1959). Some autumn departures observed as late as 10:00 for overland flights from Boston, MA, toward Narragansett Bay, RI (JJH). Spring departures observed at first light from overnight roosts on Lake Ontario (DVW). No published observations of cormorants migrating by night as well as by day, but flocks have been observed flying in late evening and few have been seen to stop and settle (Nisbet and Baird 1959).
Control And Physiology
Largest numbers seen in cool, clear weather after passage of cold fronts (Nisbet and Baird 1959). No other data.
Dorr, Brian S., Jeremy J. Hatch and D. V. Weseloh. 2014. Double-crested Cormorant (Phalacrocorax auritus), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online: http://bna.birds.cornell.edu/bna/species/441