Volume 47, No. 1

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Changes in abundance and distribution of nesting Double-crested Cormorants Phalacrocorax auritus in the San Francisco Bay area, 1975-2017


1Laney College, Geography Department, 900 Fallon Street, Oakland, CA 94607, USA (
2Point Blue Conservation Science, 3820 Cypress Drive, #11, Petaluma, CA 94954, USA
3Institute of Marine Sciences, University of California Santa Cruz, 115 McAllister Way, Santa Cruz, CA 95060, USA
4San Francisco Bay Bird Observatory, 524 Valley Way, Milpitas, CA 95035, USA
5US Fish and Wildlife Service, San Francisco Bay National Wildlife Refuge Complex, 1 Marshlands Road, Fremont, CA 94555, USA
6Audubon Canyon Ranch, Cypress Grove Research Center, P.O. Box 808, Marshall, CA 94940, USA
7Humboldt State University, Department of Wildlife, 1 Harpst Street, Arcata, CA 95521, USA †Deceased


RAUZON, M.J., ELLIOTT, M.L., CAPITOLO, P.J., TARJAN, L.M., McCHESNEY, G.J., KELLY, J.P. & CARTER, H.R. 2019. Changes in abundance and distribution of nesting Double-crested Cormorants Phalacrocorax auritus in the San Francisco Bay area, 1975-2017. Marine Ornithology 47: 127 - 138

Received 19 October 2018, accepted 13 February 2019

Date Published: 2019/04/15
Date Online: 2019/04/02
Key words: San Francisco-Oakland Bay Bridge, Double-crested Cormorant, Phalacrocorax auritus, San Francisco Bay, regional expansion, urbanized estuary


In the San Francisco Bay area, California, the Double-crested Cormorant Phalacrocorax auritus population has recovered from significant declines to reach breeding population sizes comparable to those from the late 19th century, when only one colony offshore at the South Farallon Islands (SFI) was known. The recent replacement of the bridge hosting one of the current largest colonies prompted a comprehensive assessment of Bay Area breeding population trends through 2017. Since the early 1970s, the Bay Area population has expanded from < 50 pairs at one site, SFI, to nearly 3 500 pairs at > 20 colonies, with breeding documented at 31 different locations. However, missing counts at many colonies before 2003 prevented calculation of precise, long-term growth rates. Expansion has been facilitated by cormorant adaptations to the urbanized estuary, including nesting on bridges, electrical towers, non-native trees, and managed pond levees. Breeding colonies that formed by 1984 on the San Francisco-Oakland Bay Bridge (SFOBB) and Richmond-San Rafael Bridge (RSRB) grew quickly, and in several different years totaled more than 1 000 nests. From 2003-2017, when construction of a new east span of the SFOBB (and demolition of the old span) was underway and when substantial maintenance of the RSRB occurred, the colonies on the bridges declined by 71 % and the overall Bay Area population declined by 39 %. The decline was likely due to reduced prey availability, although construction disturbance may have driven some birds from the bridges to colonies outside the region. On the Outer Coast, the colony at Hog Island was formed in 2001 and has become the largest in the study area since 2011. Nesting on artificial platforms installed on the new SFOBB east span in 2017 occurred only after demolition of the old span was complete, despite social attractions being in place since 2011. 


AINLEY, D.G. & BOEKELHEIDE, R.J. 1990. Seabirds of the Farallon Islands: ecology, dynamics, and structure of an upwelling-system community. Stanford, CA: Stanford University Press. 

AINLEY, D.G., ANDERSON, D.W. & KELLY, P.R. 1981. Feeding ecology of marine cormorants in southwestern North America. The Condor 83: 120-131.

AINLEY, D.G., STRONG, C.S., PENNIMAN, T.M., & BOEKELHEIDE, R.J. 1990. The feeding ecology of Farallon seabirds. In: AINLEY, D.G. & BOEKELHEIDE, R.J. (Eds.). Seabirds of the Farallon Islands: ecology, structure, and dynamics of an upwelling system community. Stanford, CA: Stanford University Press. pp. 51-127.

AINLEY, D.G. & LEWIS, T.J. 1974. The history of Farallon Island marine bird populations, 1854-1972. The Condor 76: 432-446.

AINLEY, D.G., SANTORA, J.A., CAPITOLO, P.J. ET AL. 2018.  Ecosystem-based management affecting Brandt's cormorant resources and populations in the Gulf of the Farallones, California. Biological Conservation 217: 407-418.

ADKINS, J.Y., ROBY, D.D., LYONS, D.E., ET AL. 2014. Review: recent population size, trends, and limiting factors for the Double-crested Cormorant in western North America. Journal of Wildlife Management 78: 1131-1142.

ANDERSON, C.D., ROBY, D.D. & COLLIS, K. 2004. Conservation implications of the large colony of Double-crested Cormorants on East Sand Island, Columbia River Estuary, Oregon, U.S.A. Waterbirds 27: 155-160.

BARTHOLOMEW, G.A. JR. 1943. The daily movements of cormorants on San Francisco Bay. The Condor 45: 3-18.

BARTON, K. 2018. MuMIn: Multi-Model Inference. R package version 1.42.1.

BOEKELHEIDE , R.J., AINLEY, D.G., HUBER, H.R. & LEWIS, T.J. 1990. Pelagic Cormorant and Double-crested Cormorant. In: AINLEY, D.G. & BOEKELHEIDE, R.J. (Eds.). Seabirds of the Farallon Islands: ecology, structure, and dynamics of an upwelling system community. Stanford, CA: Stanford University Press. pp. 195-217.

BOLANDER, L.P. & BRYANT, C.A. 1930. Some notes on Point Reyes birds. The Condor 32: 70-72.

BOUSMAN, W.G. 2007. Breeding Bird Atlas of Santa Clara County, CA. Cupertino, CA: Santa Clara Valley Audubon Society.

BRAKE, A.J., WILSON, H.A., LEONG, R. & FISH, A.M. 2014. Status of Ospreys Nesting on San Francisco Bay. Western Birds 45: 190-198.

BRITTAN, M.R., HOPKIRK, J.D. CONNERS, J.D. & MARTIN, M. 1970. Explosive spread of the oriental goby Acanthogobius flavimanus in the San Francisco Bay-Delta region of California. Proceedings of the California Academy of Sciences 38: 207-214. 

BROUGHTON, J. 2004. Prehistoric human impacts on California birds: evidence from the Emeryville Shellmound avifauna. Ornithological Monographs 56: 1-90.

CAMPBELL, K.F. & LEVALLEY, R. 1984. The nesting season: Middle Pacific Coast region. American Birds 38: 1056-1060.

CAPITOLO, P.J. 2009. Farallon Islands. In: GILLESPIE, R. (Ed.) Encyclopedia of Islands. Berkeley, CA: University of California Press. pp. 287-291. [Available online at: Accessed 18 October 2018].

CAPITOLO, P.J., CARTER, H.R., YOUNG, R.J., ET AL. 2004. Changes in breeding population size of Brandt's and Double-crested Cormorants in California, 1975-2003, unpublished report. Department of Wildlife, Humboldt State University, Arcata, California. [Available online at: Accessed 1 Aug 2018].

CAPITOLO, P.J., MCCHESNEY, G.J., CARTER, H.R., PARKER, M.W., EIGNER L.E. & GOLIGHTLY, R.T. 2014. Changes in breeding population sizes of Brandt's Cormorants Phalacrocorax penicillatus in the Gulf of the Farallones, California, 1979-2006. Marine Ornithology 42: 35-48.

CAPITOLO, P.J., CARTER, H.R., YEE, J.L. ET AL. 2019. Changes in breeding population sizes of Double-crested Cormorants (Phalacrocorax auritus) in the Humboldt Bay area, California, 1924-2017. Marine Ornithology, in press.

CARTER, H.R., MCCHESNEY, G.J., JAQUES, D.L., ET AL. 1992. Breeding populations of seabirds in California, 1989-1991: unpublished draft final report. Volumes 1 and 2.  Dixon, CA: US Fish and Wildlife Service, Northern Prairie Wildlife Research Center [Available online at: Accessed 1 Aug 2018].

CARTER, H.R., SOWLS, A.L., RODWAY, M.S., ET AL. 1995. Population size, trends, and conservation problems of the Double-crested Cormorant on the Pacific coast of North America. Colonial Waterbirds 18: 189-215.

CARTER, H.R., MCCHESNEY, G.J., TAKEKAWA, J.E., ET AL. 1996. Population monitoring of seabirds in California: 1993-1995 aerial photographic surveys of breeding colonies of Common Murres, Brandt's Cormorants and Double-crested Cormorants: unpublished final report. Dixon, CA: US Geological Survey, California Science Center.

CARTER, H.R., CAPITOLO, P.J., MCCHESNEY, G.J., MCIVER, W.R. & TAKEKAWA, J.E. 2000. Population monitoring of seabirds in California: colony and subcolony databases for 1985-1995 surveys of breeding colonies of Common Murres, Brandt's Cormorants, and Double-crested Cormorants between Point Arena and Point Conception: unpublished final report. Dixon, CA: US Geological Survey, Western Ecological Research Center; Arcata, CA: Humboldt State University, Department of Wildlife; and Newark, CA: US Fish and Wildlife Service, San Francisco Bay National Wildlife Refuge Complex.

CARTER, H.R., WILSON, U.W., LOWE, R.W., ET AL. 2001. Population trends of the Common Murre (Uria aalge californica). In: MANUWAL, D.A., CARTER, H.R., ZIMMERMAN, T.S. & ORTHMEYER, D.L. (Eds). Biology and conservation of the Common Murre in California, Oregon, Washington, and British Columbia, Volume 1: Natural history and population trends. Washington, DC: US Geological Survey, Information and Technology Report USGS/BRD/ITR-2000-0012.

CARTER, H.R., CHATWIN, T.A. & DREVER, M.C. 2018. Breeding population sizes, distributions, and trends of Pelagic, Double-Crested, and Brandt's Cormorants in the Strait of Georgia, British Columbia, 1955-2015. Northwestern Naturalist 99: 31-48.

CONOMOS, T.J. 1979. San Francisco Bay—the urbanized estuary. San Francisco, CA: American Association for the Advancement of Science-Pacific Division, pp 483.

COURTOT, K.N., ROBY, D.D., ADKINS, J.Y., LYONS, D.E., KING, D.T. & LARSEN, R.S. 2012. Colony connectivity of Pacific Coast Double-crested Cormorants based on post-breeding dispersal from the region's largest colony. Journal of Wildlife Management 76: 1462-1471.

DORR, S., HATCH, J.J., & WESELOH, D.V. 2014. Double-crested Cormorant (Phalacrocorax auritus), version 2.0. In: A.F. POOLE (Ed.) The Birds of North America. Ithaca, NY: Cornell Lab of Ornithology.

ELLIOTT, M.L., SCHMIDT, A., ACOSTA, S. ET AL. 2016. Brandt's cormorant diet (1994-2012) indicates the importance of fall ocean conditions for northern anchovy in central California. Fisheries Oceanography 25: 515-528. 

ELLIOTT, M.L., RAUZON, M.J., ROTH, J.E. & HIEB, K. 2010. Double-crested Cormorant declines in San Francisco Bay: poster presentation. Long Beach, CA: Pacific Seabird Group Annual Meeting.

EMERSON, W. 0. 1904. The Farallone Islands re-visited, 1887-1903. The Condor 6: 61-68.

GILL, R. Jr. 1977. Breeding Avifauna of the South San Francisco Bay Estuary. Western Birds 8: 1-12.

GRINNELL, J. 1915. A distributional list of the birds of California. Hollywood, CA: Cooper Ornithological Club. 

GRINNELL, J. & WYTHE, M.W. 1927. Directory to the bird-life of the San Francisco Bay region. Berkeley, CA: Cooper Ornithological Club. 

HANSEN, H.E. & SQUIRES, W.A. 1917. A list of the birds breeding in San Francisco County, California. The Condor 19: 54-62.

HATCH, J.J. 1995. Changing populations of Double-crested Cormorants. Colonial Waterbirds 18(Special Publication 1): 8-24.

HERBOLD, B.A., A.D. JASSBY & MOYLE, P.B. 1992. Status and trends report on aquatic resources in the San Francisco estuary. EPA Public Report. San Francisco, CA: San Francisco Estuary Project.

Historic Bridges: Richmond-San Rafael Bridge [Online]. Available online at: Accessed 7 August 2018].

JONES, H.P. & KRESS, S.W. 2012. A review of the world's active seabird restoration projects. Journal of Wildlife Management 76: 2-9.

MENG, L., MOYLE, P. B. & HERBOLD, B. 1994. Changes in abundance and distribution of native and introduced fishes of Suisun Marsh. Transactions of the American Fisheries Society 123: 498-507. 

MILLER, D. J. & LEA, R.N. 1972. Guide to the Coastal Marine Fishes of California. Fish Bulletin No. 157. Sacramento, CA: California Department of Fish and Game and the University of California. 

ORIANS, G.H. and PEARSON, N.E. 1979. On the theory of central place foraging. In: HORN, D.J., STAIRS, G.R. & MITCHELL, R.D. (Eds.) Analysis of Ecological Systems. Columbus, OH: Ohio State University Press, pp. 154-177.

RAUZON, M.J., SYDEMAN, W.J., ELLIOTT, M.L. & ROTH, J. 2001. Population size and breeding success of Double-crested Cormorants (Phalacrocorax auritus) on the Richmond-San Rafael Bridge, California, in 2000: unpublished report. San Francisco and Stinson Beach, CA: San Francisco State University and Point Reyes Bird Observatory. [Available online at: Accessed 18 October 2018].

R CORETEAM. 2016. R: A language and environment for statistical computing. R Foundation for Statistical Computing. Vienna, Austria. [Available online at:].

SCOTT, M. 1985. The San Francisco Bay Area: A Metropolis in Perspective. Berkeley, CA: University of California Press.

SHADISH, W.R., ZUUR, A.F., & SULLIVAN, K. J. 2014. Using generalized additive (mixed) models to analyze single case designs. Journal of School Psychology 52: 149-178.

San Francisco-Oakland Bay Bridge [Online]. Sacramento, CA: California Department of Transportation. [Available online at Accessed 3 April 2018].

Skyway [Online]. Oakland, CA: Caltrans District 4. [Available online at Accessed 3 April 2018].

SHUFORD, W.D. 1993. The Marin County Breeding Bird Atlas. Bolinas, CA: Bushtit Books.

STALLCUP, R. & WINTER, J. 1976. Middle Pacific Coast Region. American Birds 30: 118.

SOWLS, A.L., DEGANGE, A.R., NELSON, J.W. & LESTER, G.S. 1980. Catalog of California seabird colonies. FWS/OBS 37/80. Sacramento, CA: US Department of the Interior, Bureau of Land Management, Fish and Wildlife Service, Biological Services Program.

SQUIRES, W.A. 1917. Some field notes for 1917. The Condor 19: 185-186.

STENZEL, L.E., CARTER, H.R., HENDERSON, R.P., ET AL. 1995. Breeding success of Double-crested Cormorants in the San Francisco Bay Area, California. Colonial Waterbirds 18(Special Publication 1): 216-224.

STIENSTRA, T. 1998. 20 Bay area lakes for trout fishing. San Francisco Chronicle, 6 November 1998. [Available online at: Accessed 7 August 2018].

STRONG, C.M., SPEAR, L.B., RYAN, T.P. & DAKIN, R.E. 2004. Forster's Tern, Caspian Tern, and California Gull colonies in San Francisco Bay: habitat use, numbers and trends, 1982-2003. Waterbirds 27: 411-423. 

TAKEKAWA, J.E., CARTER, H.R. & HARVEY, T.E. 1990. Decline of the Common Murre in central California, 1980-1986. Studies in Avian Biology 14: 149-163.

US ARMY CORPS OF ENGINEERS (USACE). 2015. Double-crested cormorant management plan to reduce predation of juvenile salmonids in the Columbia River Estuary: Final environmental impact statement. Portland, OR: US Army Corps of Engineers, Portland District. [Available online at:; Accessed 2019 February 20].

US FISH & WILDLIFE SERVICE (USFWS). 2014.  Ecological Risk Screening Summary: Yellowfin Goby Acanthaogobius flavimanus. Washington, DC: US Fish and Wildlife Service [Available online at: Accessed 8 August 2018.]

USFWS. 2017a. Double-crested Cormorant western population status evaluation: final annual 2016 report. Portland, OR: US Fish and Wildlife Service, Migratory Birds and Habitat Programs.

USFWS. 2017b. Environmental Assessment for Issuing Depredation Permits for Double-crested Cormorant Management. Portland, OR: US Fish and Wildlife Service, Division of Migratory Bird Management 11/07/17. 

VAROUJEAN, D.H. 1979. Seabird colony catalog, Washington, Oregon, and California: unpublished report. Sacramento, CA: US Department of the Interior, Fish and Wildlife Service.

WARZYBOK, P.M., SANTORA, J.A., AINLEY, D.G. ET AL. 2018. Prey switching and consumption by seabirds in the central California Current upwelling ecosystem: Implications for forage fish management. Journal of Marine Systems 185: 25-39.

WHITE, P. 1995. The Farallon Islands: sentinels of the Golden Gate. San Francisco, CA: Scottwall Associates.

WIRES, L.R. & CUTHBERT, F.J. 2006. Historic populations of the Double-crested Cormorant (Phalacrocorax auritus): implications for conservation and management in the 21st century. Waterbirds 29: 9-37.

WIRES, L.R., CUTHBERT, F.J., TREXEL, D.R. & JOSHI, A.R. 2001. Status of Double-crested Cormorant in North America (Phalacrocorax auritus): Final report to U.S. Fish and Wildlife Service. St. Paul, MI: University of Minnesota.

WOOD, S.N. 2006. Generalized Additive Models: An Introduction with R. New York, NY: Chapman and Hall/CRC Press.

WOOD, S.N. 2011. Fast stable restricted maximum likelihood and marginal likelihood estimation of semiparametric generalized linear models. Journal of the Royal Statistical Society (B) 73: 3-36.

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