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Double-crested Cormorant, Ron Ridout
Photo © Ron Ridout

Photo: Ron Ridout
Breeding evidence - Double-crested Cormorant
Breeding evidence

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Double-crested Cormorant
Phalacrocorax auritus

Click on plot to view table of mean abundance
Elevation range:
0 - 816 m
Conserv. status:
BCRISC: Blue
Global importance
of B.C. population:
7
Number of squares
ConfirmedProbablePossiblePoint counts
11 0 29 14
Long-term BBS trends
RegionYearsTrend (conf. interv.) Reliab.
Brit. Col.1973 - 2012 -1.88 (-10.3 - 6.98)Low
Canada1970 - 2012 3.08 (-1.95 - 7.75)Low

Mean abundance by region

Bird Conservation Regions [plot]
NW Interior ForestBoreal Taiga PlainsGreat BasinNorthern RockiesN. Pacific Rainforest
    0.07 0.32
Ecoprovinces [plot]
N. Boreal Mountains Taiga Plains Boreal Plains Georgia Depression Sub-Boreal Interior
    0.32  
S. Interior Mountains Central Interior Southern Interior S. Alaska Mountains Coast & Mountains
0.07      

Mean abundance by habitat [plot]

Boreal Altai Fescue AlpineBoreal White and Black SpruceBunchgrassCoastal Douglas-fir
   0.63
Coastal Mountain-heather AlpineCoastal Western HemlockEngelmann Spruce -- Subalpine FirInterior Cedar -- Hemlock
 0.02 0.07
Interior Douglas-firInterior Mountain-heather AlpineMontane SpruceMountain Hemlock
    
Ponderosa PineSpruce -- Willow -- BirchSub-Boreal Pine -- SpruceSub-Boreal Spruce
    

Characteristics and Range The Double-crested Cormorant is a large, conspicuous and gregarious waterbird that forms breeding colonies along both Pacific and Atlantic coasts of North America, and in freshwater wetlands from the Great Lakes to the Great Plains and Great Basin. It winters along North American coasts and in the United States' Southern Coastal Plains (Dorr et al. 2014). Two subspecies likely occur in British Columbia (Dorst and Mougin 1979, Watson et al. 1991), P. a. albociliatus along the coast and possibly P. a. auritus in the interior (Dorr et al. 2014). The location of P. a. albociliatus colonies is quite fluid within its southern British Columbia to Baja California and inland range (Anderson et al. 2004).

Distribution, Abundance, and Habitat In British Columbia the Double-crested Cormorant is confined to the south coast and two recently discovered colonies at interior lakes. Ten coastal colonies were recorded during the Atlas, all in the Gulf Islands and Vancouver Harbour areas of the Georgia Depression Ecoprovince. The largest colony was on Mandarte Island (548 pairs), followed by Mitlenatch Island (327 pairs). Nesting was also recorded on Gabriola Cliffs (75 pairs), Galiano Cliffs (48 pairs), Tent Island (34 pairs), Arbutus Island (22 pairs), North Pender Island (6 pairs), Christie Rock (numbers not reported), and by Vancouver's Iron Workers Memorial Bridge (93 pairs) and beneath Granville Street Bridge (numbers not reported). Changing occupation of nest sites since records began in 1959 is a feature of Double-crested Cormorant breeding biology: the change is most apparent on Mitlenatch Island: 10 pairs first nested there in 1993, increasing to 70 pairs by 2000 (Moul and Gebauer 2002) and 327 pairs during the Atlas period.

In the interior, nesting occurs at two widely separated breeding colonies: Leach Lake in the Kootenay River valley, where breeding was first recorded in 2003, and increased to about 100 pairs by 2008; and Stum Lake in the Cariboo, where breeding was first recorded in 1993 (Moul and Gebauer 2002), and increased to at least 25 nests in 2008. An Atlas sighting of two cormorants during the breeding season at Swan Lake in the Peace River lowlands suggests nesting nearby.

Double-crested Cormorant nest sites in British Columbia include bare rock, trees, pilings, bridges, and hydro-electric towers. On the coast this species often associates with other seabirds requiring similar nesting habitats, and perhaps benefits from early warning of approaching danger. Coastal cormorants associate with Glaucous-winged Gulls, Pelagic Cormorants and Pigeon Guillemots. Double-crested Cormorant colonies in the interior are associated with Great Blue Herons and American White Pelicans.

Conservation and Recommendations Anderson et al. (2004) recommend that the coastal subspecies P. a. albociliatus be managed separately from other Double-crested Cormorants. They suggest that the coastal subspecies relocates colonies in response to local food supplies. Another factor might be disturbance and predatory attacks from Bald Eagles (Sullivan 1998, Van Damme and Colonel 2007). Maintaining and monitoring known suitable nesting sites to account for the propensity to relocate would allow for, and improve understanding of population mobility.

Acknowledgements Trudy Chatwin provided nesting records for the Strait of Georgia.

Robert W. Butler

Recommended citation: Butler, R.W. 2015. Double-crested Cormorant in Davidson, P.J.A., R.J. Cannings, A.R. Couturier, D. Lepage, and C.M. Di Corrado (eds.). The Atlas of the Breeding Birds of British Columbia, 2008-2012. Bird Studies Canada. Delta, B.C. http://www.birdatlas.bc.ca/accounts/speciesaccount.jsp?sp=DCCO&lang=en [11 Dec 2018]

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