Phalacrocorax auritus - (Lesson, 1831)
Double-crested Cormorant
Other English Common Names: double-crested cormorant
Taxonomic Status: Accepted
Related ITIS Name(s): Phalacrocorax auritus (Lesson, 1831) (TSN 174717)
French Common Names: cormoran à aigrettes
Spanish Common Names: Cormorán Orejudo
Unique Identifier: ELEMENT_GLOBAL.2.101743
Element Code: ABNFD01020
Informal Taxonomy: Animals, Vertebrates - Birds - Other Birds
Image 10746

© Dick Cannings

 
Kingdom Phylum Class Order Family Genus
Animalia Craniata Aves Suliformes Phalacrocoracidae Phalacrocorax
Genus Size: D - Medium to large genus (21+ species)
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Concept Reference
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Concept Reference: American Ornithologists' Union (AOU). 1998. Check-list of North American birds. Seventh edition. American Ornithologists' Union, Washington, D.C. [as modified by subsequent supplements and corrections published in The Auk]. Also available online: http://www.aou.org/.
Concept Reference Code: B98AOU01NAUS
Name Used in Concept Reference: Phalacrocorax auritus
Taxonomic Comments: See Siegel-Causey (1988) for analysis of relationships within family. Siegel-Causey (1988) proposed removing this species from the genus Phalacrocorax and placing it in the genus Hypoleucus; DeBenedictus (1989) concluded that the taxonomic ranks of many groups recognized by Siegel-Causey (1988) are inflated and inconsistent with other taxonomic data.
Conservation Status
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NatureServe Status

Global Status: G5
Global Status Last Reviewed: 09Apr2016
Global Status Last Changed: 20Nov1996
Ranking Methodology Used: Ranked by inspection
Rounded Global Status: G5 - Secure
Reasons: Large breeding range in North America; rapidly increasing populations.
Nation: United States
National Status: N5B,N5N (05Jan1997)
Nation: Canada
National Status: N5B,N3N4N,N5M (08Dec2017)

U.S. & Canada State/Province Status
Due to latency between updates made in state, provincial or other NatureServe Network databases and when they appear on NatureServe Explorer, for state or provincial information you may wish to contact the data steward in your jurisdiction to obtain the most current data. Please refer to our Distribution Data Sources to find contact information for your jurisdiction.
United States Alabama (S5), Alaska (S3), Arizona (S5), Arkansas (S2B,S5N), California (S4), Colorado (S4), Connecticut (S3B,S4N), Delaware (S1B), District of Columbia (S4N), Florida (SNR), Georgia (S5), Idaho (S4B), Illinois (S2), Indiana (SHB), Iowa (S3B,S5N), Kansas (S2B,S5N), Kentucky (S2B), Louisiana (S2S3B,S4N), Maine (S5B), Maryland (S1B,S3S4N), Massachusetts (S3B,S5N), Michigan (S4), Minnesota (SNRB), Mississippi (S4N), Montana (S5B), Navajo Nation (S3N), Nebraska (S4), Nevada (S4B), New Hampshire (S5), New Jersey (S1B,S4N), New Mexico (S4B,S4N), New York (S3), North Carolina (S1B,S5N), North Dakota (SNRB), Ohio (S1), Oklahoma (S3S4), Oregon (S5), Pennsylvania (SNA), Rhode Island (S2B), South Carolina (SNRB,SNRN), South Dakota (S5B), Tennessee (S2B,S4N), Texas (S3B,S5N), Utah (S3S4B,S3N), Vermont (S2B), Virginia (S3B,S4S5N), Washington (S4S5B,S4S5N), West Virginia (S2N), Wisconsin (S4B), Wyoming (S3B,S5N)
Canada Alberta (S4S5B), British Columbia (S3S4B), Labrador (S2B,SUM), Manitoba (S5B), New Brunswick (S5B,S5M), Newfoundland Island (S5B,S5M), Northwest Territories (SU), Nova Scotia (S4B), Nunavut (SUB,SUM), Ontario (S5B), Prince Edward Island (S5B), Quebec (S5), Saskatchewan (S4B), Yukon Territory (S1B)

Other Statuses

Committee on the Status of Endangered Wildlife in Canada (COSEWIC): Not at Risk (01Apr1978)
Comments on COSEWIC: This is a widespread species in Canada with a significantly increasing population. Designated Not at Risk in April 1978.
IUCN Red List Category: LC - Least concern

NatureServe Global Conservation Status Factors

Range Extent: >2,500,000 square km (greater than 1,000,000 square miles)
Range Extent Comments: BREEDING: southeastern Bering Sea and southern Alaska; southern British Columbia eastward through Manitoba to coastal Quebec and Newfoundland, south (in isolated colonies) to Baja California, coastal Sonora, central Chihuahua, central Durango, south-central Arizona, southern New Mexico, southern Texas, Gulf Coast, Florida, northern Bahamas, Cuba, Yucatan Peninsula, and Belize (Johnsgard 1993, AOU 1998). Breeding range in North America has expanded in recent years (Johnsgard 1993). Extirpated from Amchitka Island, Alaska, perhaps due to predation by arctic fox (ALOPEX LAGOPUS; Siegel-Causey et al. 1991). Occurs throughout most of the coastal breeding range and beyond when not breeding. NON-BREEDING: Pacific coast from Aleutians and southern Alaska south to Baja California and Nayarit; inland from Washington and Montana south to California and northeastern Colorado, southern Minnesota, and the Great Lakes south to northwestern Mexico, Oklahoma, Texas, and the Gulf states; and along the Atlantic coast, from Lake Ontario and New England south to Florida, Bermuda, the Bahamas, Greater Antilles, Yucatan Peninsula, and northern Belize (AOU 1998).

Number of Occurrences: > 300
Number of Occurrences Comments: In 1994, 852 colonies throughout North America (Tyson et al. 1997); number of defined occurrences may be somewhat lower.

Population Size: 100,000 to >1,000,000 individuals
Population Size Comments: Widespread and increasing. In 1994, estimated at least 372,000 nesting pairs throughout North America (Tyson et al. 1997). Relative abundance recorded on North American Breeding Bird Survey (BBS) survey-wide 1966-1996 was 0.76 birds per route. Highest relative abundance recorded in Minnesota (2.64 birds per route; Sauer et al. 1997). In winter, survey-wide Christmas Bird Count (CBC) shows 11.96 birds per 100 survey hours, 1959-1988. Highest CBC relative abundance recorded in North Carolina during the same period (170.64 birds per 100 survey hours; Sauer et al. 1996). High winter densities also occur in southern Florida, northern South Carolina, and along the lower Colorado River valley in the southwestern U.S. (Root 1988).

Overall Threat Impact Comments: PERSECUTION: Has long been hunted for both eggs and meat. Persecuted because thought to compete with fishermen. Hunted illegally; in June of 1998, over 800 birds were shot in eastern Lake Ontario and 20 were shot in 1994 on Four Brothers Island, New York. Also hunted legally; in Quebec, Canada, a government-sponsored control program involves shooting adults, destroying nests, and spraying eggs with an oily substance that asphyxiates the embryos (QBW 1999). U.S. Fish and Wildlife Service permits the lethal take of cormorants, without a permit, on catfish and bait fish farms in 12 southeastern states and Minnesota, where economic impacts have been well-documented and non-lethal control has proven ineffective (USFWS 1999a). PESTICIDES: Contamination by organochlorine pesticides greatly reduced reproductive success during the 1950s and 1960s significantly reducing populations along the Great Lakes and in other areas (Anderson et al. 1969, cited in INRIN 1999; Weseloh et al. 1983, cited in USFWS 1999b). Eggshell thinning due to exposure to DDE, DDT, and PCB's widely reported during this period (INRIN 1999, USFWS 1999a). By the early 1970s, eggshells from the Great Lakes region were nearly 30% thinner than normal (Weseloh and Collier 1999). Contamination caused reproductive failure, and chicks that hatched sometimes had crossed bills, club feet, and eye and skeletal deformities (USFWS 1999a). Deformities resulting from the ingestion of PCBs have been noted in the vicinity of Green Bay, Wisconsin (Ehrlich et al. 1992). Populations increased in New England beginning 1970 after the use of these pesticides was banned; did not increase in other areas until the 1980s (USFWS 1999b). PREDATION: Predation of eggs and young by crows and ravens (CORVUS spp.) and gulls (LARUS spp.; INRIN 1999). Verbeek (1982) reports that crows were responsible for the destruction of 22 percent of eggs (first clutch) in British Columbia. Also, temporary food shortages may be a possible limiting factors. HABITAT: Nesting habitat may become an important limiting factor (USFWS 1999a). See also Spendelow and Patton 1988; Carroll 1988; Johnsgard 1993; Markham, 1978 COSEWIC report; Hyslop and Kennedy 1992; Chapdelaine and Brousseau 1992; Vermeer and Sealy 1984; Lensink 1984; Buckley and Buckley 1984).

Short-term Trend: Increase of >10%
Short-term Trend Comments: From 1973 to 1993, Great Lakes population increased over 300-fold to over 38,000 pairs; a historic high (Weseloh and Collier 1999). Along St. Lawrence River, have increased from 12,000 pairs in 1979 to 22,000 pairs in 1990 (QBW 1999). Now increasing almost everywhere. Although BBS and other roadside surveys are not the most appropriate census method for colonial-nesting water birds trend data still provides useful information. Survey-wide increase according to BBS 1966-1996 (6.8 percent annual change; P = 0.00; n = 327). Greatest percent increase in central region (22.7 percent annual change; P = 0.00; n = 77) for same period. No significant decreases for periods 1966-1999, 1966-1979, or 1980-1996 (Sauer et al. 1997). In winter, CBC 1959-1988 indicates survey-wide increase (7.3 percent annual change; P less than 0.01; n = 790; Sauer et al. 1996).

Long-term Trend: Increase of >25%
Long-term Trend Comments: Declined in the 1960s and subsequently recovered. Largest decline in the Great Lakes population largely due to effects of DDT. Great Lakes population decreased by 86 percent from approximately 900 in the early 1950s to a mere 125 in 1973. Disappeared as a nesting bird on Lakes Michigan and Superior and only about ten pairs remained on Lake Ontario (Weseloh and Collier 1999).

Other NatureServe Conservation Status Information

Distribution
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Global Range: (>2,500,000 square km (greater than 1,000,000 square miles)) BREEDING: southeastern Bering Sea and southern Alaska; southern British Columbia eastward through Manitoba to coastal Quebec and Newfoundland, south (in isolated colonies) to Baja California, coastal Sonora, central Chihuahua, central Durango, south-central Arizona, southern New Mexico, southern Texas, Gulf Coast, Florida, northern Bahamas, Cuba, Yucatan Peninsula, and Belize (Johnsgard 1993, AOU 1998). Breeding range in North America has expanded in recent years (Johnsgard 1993). Extirpated from Amchitka Island, Alaska, perhaps due to predation by arctic fox (ALOPEX LAGOPUS; Siegel-Causey et al. 1991). Occurs throughout most of the coastal breeding range and beyond when not breeding. NON-BREEDING: Pacific coast from Aleutians and southern Alaska south to Baja California and Nayarit; inland from Washington and Montana south to California and northeastern Colorado, southern Minnesota, and the Great Lakes south to northwestern Mexico, Oklahoma, Texas, and the Gulf states; and along the Atlantic coast, from Lake Ontario and New England south to Florida, Bermuda, the Bahamas, Greater Antilles, Yucatan Peninsula, and northern Belize (AOU 1998).

U.S. States and Canadian Provinces

Due to latency between updates made in state, provincial or other NatureServe Network databases and when they appear on NatureServe Explorer, for state or provincial information you may wish to contact the data steward in your jurisdiction to obtain the most current data. Please refer to our Distribution Data Sources to find contact information for your jurisdiction.
Color legend for Distribution Map
NOTE: The maps for birds represent the breeding status by state and province. In some jurisdictions, the subnational statuses for common species have not been assessed and the status is shown as not-assessed (SNR). In some jurisdictions, the subnational status refers to the status as a non-breeder; these errors will be corrected in future versions of these maps. A species is not shown in a jurisdiction if it is not known to breed in the jurisdiction or if it occurs only accidentally or casually in the jurisdiction. Thus, the species may occur in a jurisdiction as a seasonal non-breeding resident or as a migratory transient but this will not be indicated on these maps. See other maps on this web site that depict the Western Hemisphere ranges of these species at all seasons of the year.
Endemism: occurs (regularly, as a native taxon) in multiple nations

U.S. & Canada State/Province Distribution
United States AK, AL, AR, AZ, CA, CO, CT, DC, DE, FL, GA, IA, ID, IL, IN, KS, KY, LA, MA, MD, ME, MI, MN, MS, MT, NC, ND, NE, NH, NJ, NM, NN, NV, NY, OH, OK, OR, PA, RI, SC, SD, TN, TX, UT, VA, VT, WA, WI, WV, WY
Canada AB, BC, LB, MB, NB, NF, NS, NT, NU, ON, PE, QC, SK, YT

Range Map
Note: Range depicted for New World only. The scale of the maps may cause narrow coastal ranges or ranges on small islands not to appear. Not all vagrant or small disjunct occurrences are depicted. For migratory birds, some individuals occur outside of the passage migrant range depicted. For information on how to obtain shapefiles of species ranges see our Species Mapping pages at www.natureserve.org/conservation-tools/data-maps-tools.

Range Map Compilers: NatureServe, 2002


U.S. Distribution by County Help
State County Name (FIPS Code)
CA Alameda (06001), Del Norte (06015)*, Fresno (06019), Humboldt (06023)*, Lake (06033), Lassen (06035)*, Mariposa (06043), Monterey (06053)*, Napa (06055), Sacramento (06067), San Diego (06073), San Francisco (06075), San Mateo (06081), Santa Barbara (06083), Sonoma (06097)*, Ventura (06111)
CT Fairfield (09001)*, Hartford (09003)*, New Haven (09009)*, New London (09011)
IA Allamakee (19005), Clinton (19045), Fremont (19071), Johnson (19103)
ID Ada (16001), Bannock (16005), Bear Lake (16007), Bingham (16011), Blaine (16013), Bonner (16017), Boundary (16021), Camas (16025), Canyon (16027), Caribou (16029), Cassia (16031), Elmore (16039), Franklin (16041), Fremont (16043), Gem (16045), Gooding (16047), Jefferson (16051), Kootenai (16055), Lemhi (16059), Nez Perce (16069), Owyhee (16073), Power (16077), Twin Falls (16083)
IN Daviess (18027)*, Henry (18065)*, Huntington (18069)*, La Porte (18091)*, Posey (18129)*
KY Ballard (21007)*, Calloway (21035), Fulton (21075)*, Henderson (21101)*, Jefferson (21111)
MN Beltrami (27007), Cass (27021), Chippewa (27023), Clearwater (27029), Lac Qui Parle (27073), Lincoln (27081), Marshall (27089), Otter Tail (27111), St. Louis (27137), Swift (27151)
MS Bolivar (28011)*, Grenada (28043), Harrison (28047)*, Jackson (28059)*, Tunica (28143)*
NC Carteret (37031), Chatham (37037), Craven (37049)
OH Lucas (39095)
RI Newport (44005)
WA Grant (53025)+, Pend Oreille (53051)+, Thurston (53067)+, Wahkiakum (53069)+, Yakima (53077)+
* Extirpated/possibly extirpated
U.S. Distribution by Watershed Help
Watershed Region Help Watershed Name (Watershed Code)
01 Lower Connecticut (01080205)+*, Narragansett (01090004)+, Saugatuck (01100006)+*
02 Long Island Sound (02030203)+, Broadkill-Smyrna (02040207)+
03 Pamlico Sound (03020105)+, Lower Neuse (03020204)+, White Oak River (03020301)+, Haw (03030002)+, Mississippi Coastal (03170009)+*
04 St. Louis (04010201)+
05 Salamonie (05120102)+*, Lower Wabash (05120113)+*, Driftwood (05120204)+*, Lower East Fork White (05120208)+*, Silver-Little Kentucky (05140101)+, Highland-Pigeon (05140202)+*
06 Kentucky Lake (06040005)+
07 Mississippi Headwaters (07010101)+, Leech Lake (07010102)+, Upper Minnesota (07020001)+, Hawk-Yellow Medicine (07020004)+, Coon-Yellow (07060001)+, Apple-Plum (07060005)+, Middle Iowa (07080208)+, Kankakee (07120001)+*
08 Lower Mississippi-Memphis (08010100)+*, Obion (08010202)+*, Lower Mississippi-Helena (08020100)+*, Coldwater (08030204)+*, Yalobusha (08030205)+, Big Sunflower (08030207)+*
09 Buffalo (09020106)+, Thief (09020304)+, Clearwater (09020305)+, Lower Red (09020311)+, Vermilion (09030002)+, Little Fork (09030005)+
10 Keg-Weeping Water (10240001)+
16 Bear Lake (16010201)+, Middle Bear (16010202)+
17 Lower Kootenai (17010104)+, Pend Oreille Lake (17010214)+, Pend Oreille (17010216), Upper Spokane (17010305)+, Lower Crab (17020015), Upper Yakima (17030001), Idaho Falls (17040201)+, Upper Henrys (17040202)+, American Falls (17040206)+, Blackfoot (17040207)+, Portneuf (17040208)+, Lake Walcott (17040209)+, Raft (17040210)+, Upper Snake-Rock (17040212)+, Beaver-Camas (17040214)+, Big Wood (17040219)+, Camas (17040220)+, Little Wood (17040221)+, C. J. Idaho (17050101)+, Middle Snake-Succor (17050103)+, Lower Boise (17050114)+, Middle Snake-Payette (17050115)+, Payette (17050122)+, Lower Snake-Asotin (17060103)+, Pahsimeroi (17060202)+, Middle Salmon-Panther (17060203)+, Clearwater (17060306)+, Lower Columbia (17080006), Chetco (17100312)+*, Puget Sound (17110019)
18 Smith (18010101)+*, Gualala-Salmon (18010109)+*, Lower American (18020111)+, Upper Cache (18020116)+, Lower Sacramento (18020163)+, Upper Dry (18030009)+, Middle San Joaquin-Lower (18040001)+, San Joaquin Delta (18040003)+, Upper Mokelumne (18040012)+, San Pablo Bay (18050002)+, San Francisco Bay (18050004)+, San Francisco Coastal South (18050006)+, Central Coastal (18060006)+*, Santa Barbara Channel Islands (18060014)+, San Pedro Channel Islands (18070107)+, San Diego (18070304)+, Honey-Eagle Lakes (18080003)+*
+ Natural heritage record(s) exist for this watershed
* Extirpated/possibly extirpated
Ecology & Life History
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Reproduction Comments: Time of nesting varies geographically, with local variations, and among different years a particular colony. Nesting begins in winter in Florida, as late as early June in southern Alaska. Clutch size usually one to seven (average typically three or four). Incubation 24-33 days (average around 28-30), by both sexes in turn. Hatching success was 54-75% in three studies. Survival from hatching to fledging was 72-95% in two studies. First flight to water at about 35-42 days. Independent at about 9-10 weeks. Usually first breeds at three years, sometimes at two years, rarely at one year. Renesting following loss of clutch is fairly common. Nest in relatively dense colonies; nests only 0.6 - 2.0 meters apart (Hatch and Weseloh 1999). New colonies may be abandoned within a few years, but once well established, likely to persist (Hatch and Weseloh 1999). See Johnsgard (1993) for further information.
Ecology Comments: Typically forages within about 20 km of roost site (Johnsgard 1993). No available information on interannual fidelity to colony; median distance of breeding birds to their natal site was < 25 kilometres (Dolbeer 1991). Increased sea surface temperatures, such as those associated with El Nino events, were correlated with decreases in nesting populations in Washington (Wilson 1991). Vigorously defends eggs and young against avian predators (Ehrlich et al. 1992), though large gulls, crows, and ravens are significant predators on eggs and young in some areas.
Non-Migrant: Y
Locally Migrant: Y
Long Distance Migrant: Y
Mobility and Migration Comments: Northern coastal and especially interior populations migrate southward for nonbreeding season; migratory tendency is stronger on east coast than on west coast. Usually follows river valleys, coastlines, and water courses. Migrates day or night (Palmer 1962). East of the Rockies, migrates southward from northern latitudes in October-November, northward in April-May; breeders from the central and eastern parts of Canada and the northern U.S. winter mainly in the southern U.S. between Texas and Florida, with considerable overlap of different breeding populations on the wintering grounds; there is little intermixing of birds from east and west of the Rockies (Dolbeer 1991).
Marine Habitat(s): Near shore
Estuarine Habitat(s): Bay/sound, Lagoon, River mouth/tidal river, Tidal flat/shore
Riverine Habitat(s): BIG RIVER, Low gradient
Lacustrine Habitat(s): Deep water
Palustrine Habitat(s): FORESTED WETLAND, Riparian
Terrestrial Habitat(s): Bare rock/talus/scree, Cliff
Special Habitat Factors: Standing snag/hollow tree
Habitat Comments: Lakes, ponds, rivers, lagoons, swamps, coastal bays, marine islands, and seacoasts; usually within sight of land. Nests on the ground or in trees in freshwater situations, and on coastal cliffs (usually high sloping areas with good visibility). See Spendelow and Patton (1988) for further details on nesting sites in different geographic areas.
Adult Food Habits: Piscivore
Immature Food Habits: Piscivore
Food Comments: Feeds opportunistically on fishes (usually less than 13 cm long); dives from surface of water; usually feeds in water < 15 m deep. Accused of reducing sport fish populations in New York, but this contention has not been documented (Carroll 1988). Eats mostly schooling fishes (in marine waters, mainly slow-moving species of bottom and mid-water), sometimes aquatic invertebrates and rarely small vertebrates other than fishes. Sometimes forages in compact flocks.
Adult Phenology: Crepuscular, Diurnal
Immature Phenology: Crepuscular, Diurnal
Colonial Breeder: Y
Length: 81 centimeters
Weight: 1818 grams
Economic Attributes
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Economic Comments: Regarded as a nuisance when eating catish from catfish farm ponds (Conniff 1991).
Management Summary
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Management Requirements: In Illinois, a public viewing area used once a week by humans 229 m from a rookery did not cause any overt responses from nesting birds (DeMauro 1993). See Conniff (1991) for an informal discussion of some methods to keep cormorants out of catfish ponds.
Population/Occurrence Delineation
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Group Name: Cormorants

Use Class: Breeding
Subtype(s): Foraging Area, Breeding Colony
Minimum Criteria for an Occurrence: Evidence of historical breeding , or current and likely recurring breeding, at a given location, minimally a reliable observation of one or more breeding pairs in appropriate habitat. Be cautious about creating EOs for observations that may represent single breeding events outside the normal breeding distribution.
Mapping Guidance: Map foraging areas as separate polygons if they are separated from the breeding colony by areas simply flown over on commuting routes.
Separation Barriers: None.
Separation Distance for Unsuitable Habitat: 5 km
Separation Distance for Suitable Habitat: 10 km
Separation Justification: Occurrences include nesting areas and associated nesting-season foraging areas, but separation distance pertains to nesting areas (breeding colonies). Thus different breeding occurrences may overlap if birds from different nesting areas forage in the same area. Separation distance is not intended to delineate demographically independent populations or metapopulations (such units would be quite large) but rather serves to circumscribe breeding occurrences that are of practical size for conservation/management use.

Unsuitable habitat: upland areas not closely bordering water.

Cormorants usually nest in relatively dense colonies. Within-colony movement limited, but individuals can forage many kilometers from colony. Double-crested Cormorants on the Farallon Islands regularly fly a roundtrip of at least 70 kilometers to feed (Ainley and Boekelheide 1990); in Massachusetts, most feed much closer to colony than that, but some travelled 30 kilometers out (Hatch and Weseloh 1999). Pelagic Cormorants ranged up to 15 kilometers from Farallon Islands, but usually stayed much closer (Ainley and Sanger 1979). Great Cormorants had a maximum foraging range of 37 kilometers in Nova Scotia (Ross 1974-1976) and France; in France returned repeatedly to restricted feeding sites (Gremillet et al. 1999).

Philopatry to proximity of natal colony suggested by median band recovery distance of only 25 kilometers for Double-crested Cormorants at least three years old (Dolbeer 1991); substantial fidelity to previous-year's nest site in Great Cormorants (Schjorring et al. 2000). However, an expanding group of double-crested cormorant colonies in Lake Huron, Michigan, included individuals from most breeding sites within 230 km (Belyea et al. in press, cited by Hatch and Weseloh 1999).

Inferred Minimum Extent of Habitat Use (when actual extent is unknown): 5 km
Inferred Minimum Extent Justification: Somewhat arbitrary, but well within foraging distances of this group. Not applicable for colonies that are distinctly separate from foraging grounds.
Date: 26Apr2004
Author: Cannings, S., and G. Hammerson
Notes: Includes all cormorants.

Use Class: Nonbreeding
Subtype(s): Foraging area, Loafing site, Roosting site
Minimum Criteria for an Occurrence: Evidence of past or present presence of flocks of nonbreeding birds (including nonbreeding birds within the breeding season and breeding individuals outside the breeding season) and potential recurring presence at a given location. Normally only areas where concentrations greater than 25 birds regularly occur for at least 20 days per year would be deemed EOs. Be cautious about creating EOs for observations that may represent single events.
Mapping Guidance: Roosting and loafing sites that are separated from foraging concentration areas by commuting routes should be mapped as separate source feature polygons.
Separation Barriers: None.
Separation Distance for Unsuitable Habitat: 10 km
Separation Distance for Suitable Habitat: 10 km
Alternate Separation Procedure: Roost and loafing sites associated with specific foraging concentration areas should be included with the foraging occurrence, even if they are separated by more than the nominal separation distance.
Separation Justification: Separation distance is arbitrary but intended to yield occurrences that are not impractically large. Occurrences are defined primarily on the basis of areas supporting concentrations of foraging cormorants, rather than on the basis of distinct populations. Roost and loafing sites associated with specific foraging concentration areas should be treated as one occurrence, even if they are separated by more than the nominal separation distance.
Date: 26Apr2004
Author: Cannings, S., and G. Hammerson
Notes: Includes all cormorants.
Population/Occurrence Viability
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U.S. Invasive Species Impact Rank (I-Rank) Not yet assessed
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Authors/Contributors
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NatureServe Conservation Status Factors Edition Date: 30Nov1999
NatureServe Conservation Status Factors Author: KOENEN, M.; revisions by D.W. MEHLMAN.
Element Ecology & Life History Edition Date: 17May1995
Element Ecology & Life History Author(s): HAMMERSON, G., REVISED BY S. CANNINGS

Zoological data developed by NatureServe and its network of natural heritage programs (see Local Programs) and other contributors and cooperators (see Sources).

References
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  • Ainley, D. G., and G. A. Sanger. 1979. Trophic relationships of seabirds in the northeastern Pacific Ocean and Bering Sea. Pp. 95-122 IN J. C. Bartonek and D. N. Nettleship, editors. Conservation of marine birds of northern North America. U.S. Department of Interior, FIsh and Wildlife Service, Wildlife Research Report 11.

  • Ainley, D. G., and R. J. Boekelheide, editors. 1990. Seabirds of the Farallon Islands. Stanford University Press, Stanford, CA.

  • Alabama Ornithological Society. 2006. Field checklist of Alabama birds. Alabama Ornithological Society, Dauphin Island, Alabama. [Available online at http://www.aosbirds.org/documents/AOSChecklist_april2006.pdf ]

  • American Ornithologists Union (AOU). 1998. Check-list of North American Birds. 7th edition. American Ornithologists Union, Washington, D.C. 829 pages.

  • American Ornithologists' Union (AOU). 1983. Check-list of North American Birds, 6th edition. Allen Press, Inc., Lawrence, Kansas. 877 pp.

  • American Ornithologists' Union (AOU). 1998. Check-list of North American birds. Seventh edition. American Ornithologists' Union, Washington, D.C. [as modified by subsequent supplements and corrections published in The Auk]. Also available online: http://www.aou.org/.

  • Anderson, D. W., J. J. Hickey, R. W. Risebrough, D. F. Hughes, and R. E. Christensen. 1969. Significance of chlorinated hydrocarbon residues to breeding pelicans and cormorants. Can. Field Nat. 83: 91-112.

  • Andrews, R. R. and R. R. Righter. 1992. Colorado Birds. Denver Museum of Natural History, Denver. 442 pp.

  • Aquin, P. 1999. Évaluation de la situation des groupes taxonomiques d'amphibiens du Québec. Ministère de l'Environnement et de la Faune. 2 pages.

  • Aquin, P. 1999. Évaluation de la situation des groupes taxonomiques des oiseaux du Québec. Ministère de l'Environnement et de la Faune. 13 pages.

  • B83COM01NAUS - Added from 2005 data exchange with Alberta, Canada.

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