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BC Conservation Data Centre: Conservation Status Report

Nannopterum auritum
Double-crested Cormorant

 
Scientific Name: Nannopterum auritum
Scientific Name Synonyms: Phalacrocorax auritus
English Name: Double-crested Cormorant
   
Provincial Status Summary
Status: S3S4
Date Status Assigned: January 11, 2013
Date Last Reviewed: March 05, 2015
Reasons: There are a small number of colonies with fluctuating numbers; however there have been a few colonies establishing in disturbed situations and increases in numbers at the interior colonies. There were a number of observations of Double-crested Cormorants during the breeding season in locations other than the known colonies. If these are confirmed as colonies the rank will be re-assessed.


 
Range
Range Extent: E = 5,000-20,000 square km
Range Extent Comments: Two disjunct populations. Breeding is primarily in the Strait of Georgia (Campbell et al. 1990). Outside the breeding period Double-crested Cormorants can be found in sheltered waters throughout the coast, but are most abundant in the Strait of Georgia and Juan de Fuca Strait. Vagrants occasionally observed on interior lakes. Recently discovered breeding in the interior on islands in Stum Lake (M. Chutter, pers. comm.) and on the Creston Valley Wildlife Management Area.
Area of Occupancy (km2): U = Unknown
Linear Distance of Occupancy: U = Unknown
 
Occurrences & Population
Number of Occurrences: B = 6 - 20
Comments: [2 + in the interior plus more identified during the BBA). ] About 12 colonies are currently active; eleven on the coast and one in the central interior (T. Chatwin, pers. comm.).
Number of Occurrences with Good Viability / Ecological Integrity: Rank Factor not assessed
Number of Occurrences Appropriately Protected & Managed: DE = 13 to >40
Comments: Most significant colonies are protected as ecological reserves. An exception is the colony on Mandarte Island which is an Indian Reserve. The Stum Lake colony is protected in a Class A Provincial Park.
Population Size: D = 1,000 - 2,500 individuals
Comments: Estimate of 98 pair at Creston and 25 pairs at Stum in 2008 and 403 pairs on the coast (Adkins and Rory 2010).
Breeding population is estimated to be about 1200 on the coast (Chatwin 2002; T. Chatwin, pers. comm.). Fewer than 10 pairs breed at Stum Lake (M. Chutter, pers. comm.).
 
Threats (to population, occurrences, or area affected)
Degree of Threat: Moderate and imminent threat
Comments: The primary cause of the decline at coastal sites is believed to be increased nest predation by Glaucous-winged Gulls and Northwestern Crows, which in turn is probably the result of an increase in Bald Eagle disturbance at the colonies. (I. Moul pers. comm.; T. Sullivan pers. comm.). Colonies are also threatened in a similar manner by human disturbance (Rodway 1991). Oil spills (Burger and Fry 1993), and gill-net entanglement (DeGange et al. 1993) are less serious threats. The small breeding population on the coast is concentrated in an area of high human activity and pollution. While Pacific populations of cormorants were severely affected in the past by organochlorine pesticides, there is no evidence that these toxins are currently a significant problem. It is even less clear what long-term effect industrial pollutants such as polychlorinated biphenyls (PCBs), polychlorinated dibenzodioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) will have. These last three compounds have been found at elevated levels in British Columbia's Double-crested Cormorants (Elliot and Noble 1993).
 
Trend (in population, range, area occupied, and/or condition of occurrences)
Short-Term Trend: HI = Increase of >10%
Comments: Stable with increases in area and by the interior populations and via the CBC.
If short term are defined as 10 years, there has been essentially no change in numbers between 1992 and 2002, however within that time there was a major increase in 1993 to 1995 which would show a 50% decline from those numbrs to present (Chatwin 2001). There also are the decreases as mentioned below from the mid-80's.
Both breeding success and subsequently the breeding population have declined dramatically on the coast since the mid 1980s (I. Moul pers. comm.; T. Sullivan, pers. comm.). Rodway (1991) reported a coastal breeding population of over 2000; this has since declined to about 800 pairs in 1998 (T. Sullivan, pers. comm.). The 15 coastal colonies reported by Rodway (1991) have dwindled to about nine in 1998 (I. Moul, pers. comm.; T. Sullivan, pers. comm.). In the mid-1980s first clutches failed and nestlings were late leaving nests (Sullivan 1987), but in the 1990s there have been almost total breeding failures at many key colonies (I. Moul pers. comm.; T. Sullivan, pers. comm.). At Mandarte Island, which until recently was by far the largest colony, the number of active nests declined from 972 in 1987 to 178 in 1998 (I. Moul, pers. comm.). In the interior, cormorants have recently established a breeding colony, but fewer than 10 pairs nest there (M. Chutter, pers. comm.)
Long-Term Trend: I = Increase of >25%
Comments: Prior to 1927 Double-crested Cormorants were not known to breed in BC.
 
Other Factors
Intrinsic Vulnerability: C=Not intrinsically vulnerable
Environmental Specificity: B=Narrow. Specialist or community with key requirements common.
Other Rank Considerations:
 
Information Gaps
Research Needs:
Inventory Needs: Larger colonies should be monitored annually using standardized methods (Resources Inventory Committee 1997) to detect trends in population and reproductive success. Other colonies and winter concentrations should be censused on a regular basis to monitor population trends and persistence of breeding colonies. Surveyors should check for chick malformations potentially caused by environmental contaminants. Double-crested Cormorant surveys at Stum Lake should be included with American White Pelican surveys.
 
Stewardship
Protection:
Management: Unprotected breeding colonies (e.g., Mandarte Island) should be secured through habitat acquisition, administrative transfer, or long-term stewardship agreement as appropriate. Area management plans for each colony should be developed in cooperation with all affected government agencies and stakeholders. Guidelines to reduce human disturbance near cormorant colonies should be developed and implemented. Public information and education products should be developed as part of a overall plan to increase public awareness of vulnerability of cormorant colonies to human disturbance, to reduce disturbance, and to encourage conservation of breeding habitats. Marine oil spill response plans (e.g., Howes and Wainwright 1993) should be evaluated and amended as necessary to address the needs of Double-crested Cormorant populations. More research is needed on the effect of disturbance on breeding success in coastal colonies. Eggshell fragments and other tissues should be collected regularly from selected colonies for analysis of environmental contaminants. Movement patterns of breeding birds among colonies should be investigated. Determine subspecies of Double-crested Cormorant at Stum Lake colony. Assess level of kill at salmon farms.
 
Version
Author: S. Cannings, T. Chatwin and L. Ramsay
Date: February 20, 2003
 
References
Adkins, J.Y and D.D. Roby (prepared by). 2010. A status assessment of the Double-crested Cormorant (Phalacrocorax auritus) in Western North America (1998-2009). Prepared for the Army Core of Engineers, Portland, Or. 69pp
Burger, A.E., and D.M. Fry. 1993. Effects of oil pollution on seabirds in the northeast Pacific. Pages 254-263 in K. Vermeer, K. Briggs, K. Morgan, and D. Seigel-Causey, eds. The status, ecology, and conservation of marine birds in the North Pacific. Can. Wildl. Serv. Spec. Publ., Ottawa.
Campbell, R.W., N.K. Dawe, I.McT. Cowan, J.M. Cooper, G. Kaiser, and M.C.E. McNall. 1990. The Birds of British Columbia, Vol. 1. Nonpasserines: Introduction, Loons through Waterfowl. Royal B.C. Mus. in association with Environ. Can., Can. Wildl. Serv. 514pp.
Cannings, R.J. 1998. The Birds of British Columbia - a taxonomic catalogue. B.C. Minist. Environ., Lands and Parks, Wildl. Branch, Victoria, Wildl. Bull. B-86. 266pp.
DeGange, A., et al. 1993. Losses of seabirds in gill nets in the North Pacific. Pages 204-211 in K. Vermeer, K. Briggs, K. Morgan, and K. Seigel-Causey, eds. The status, ecology and conservation of marine birds in the North Pacific. Can. Wildl. Serv. Spec. Publ., Ottawa.
Elliot, J.E., and D.G. Noble. 1993. Chlorinated hydrocarbon contaminants in marine birds of the temperate North Pacific. Pages 241-253 in K. Vermeer, K. Briggs, K. Morgan, and D. Seigel-Causey, eds. The status, ecology and conservation of marine birds in the North Pacific. Can. Wildl. Serv. Spec. Publ., Ottawa, ON.
Hobson, K.A. 1997. Pelagic Cormorant (Phalacrocorax pelagicus). in A. Poole and F. Gill, eds. The Birds of North America. No. 282. Acad. Nat. Sci., Philadelphia, PA, and Am. Ornithol. Union, Washington, DC. 28pp.
Howes, D.E., and P. Wainwright. 1993. Coastal resources and oil spill response atlas for the southern Strait of Georgia. Environ. Emergencies Coordination Off., B.C. Minist. Environ., Lands and Parks, Victoria, BC.
Resource Inventory Committee. 1997f. DRAFT. Standardized Inventory Methodologies for Components of British Columbia's Biodiversity: Sea Birds, version 1.1 (draft). Prepared for Resour. Inventory Comm., B.C. Minist. Environ., Lands and Parks, Victoria, BC.
Robertson, I. 1974. The food of nesting Double-crested and Pelagic cormorants at Mandarte Island, British Columbia, with notes on feeding ecology. Condor 76:346-348.
Rodway, M.S. 1991. Status and conservation of breeding seabirds in British Columbia. Pages 43-102 in J.P. Croxall, ed. Seabird status and conservation: a supplement. Int. Counc. for Bird Preservation Tech. Publ. No. 11. Cambridge. U.K.
Sauer, J.R., J.E. Hines, G. Gough, I. Thomas, and B.G. Peterjohn. 1997a. The North American Breeding Bird Survey Results and Analysis. Version 96.3. Online. Patuxent Wildlife Research Center, Laurel, MD. Available: http://www.mbr.nbs.gov/bbs/bbs.html.
Sauer, J.R., S. Schwartz, and B. Hoover. 1996. The Christmas bird count home page. Version 95.1. Patuxent Wildl. Res. Center, Laurel, MD. Online. Available: http://www.mbr.nbs.gov/bbs/cbc.html
Siegel-Causey, D., and N.M. Litvinenko. 1993. Status, ecology and conservation of shags and cormorants of the temperate North Pacific. Pages 122-130 in K. Vermeer, K. Briggs, K. Morgan, and D. Seigel-Causey, eds. The Status, Ecology and Conservation of Marine Birds in the North Pacific. Can. Wildl. Serv. Spec. Publ., Ottawa, ON.
 

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Suggested Citation:

B.C. Conservation Data Centre. 2003. Conservation Status Report: Nannopterum auritum. B.C. Minist. of Environment. Available: https://a100.gov.bc.ca/pub/eswp/ (accessed May 14, 2024).