• Author(s): Kees Vermeer and Leo Rankin Source: The Murrelet, Vol. 65, No. 1 (Spring, 1984), pp. 1-9 Published by: Society for Northwestern Vertebrate Biology Stable URL: http://www.jstor.org/stable/3534203 (partial listing only)
• ABSTRACT- Breeding populations of Double-crested (Phalacrocorax auritus) and Pelagic Cormorants (P. pelagicus) were surveyed in the Strait of Georgia, British Colum-bia, in 1983. Double-crested Cormorant numbers have increased 2.4-fold and Pelagic Cormorant numbers 1.1-fold since 1975. Double-crested Cormorant populations are presently not only increasing in British Columbia but all across Canada and in the northeastern United States. These increases are thought to be the result of decreased disturbance and persecution by man.
• The following table is presented in partial form only:

• http://www.env.gov.bc.ca/wildlife/wsi/reports/4382_WSI_4382_RPT.PDF (see complete report)
  Authors:Trudy A. Chatwin, Monica H. Mather, Tanya Giesbrecht May 2001
  Abstract Since the early 1990’s Double-crested and Pelagic Cormorant have shown alarming declines in nesting populations in the Strait of Georgia. This study was initiated in 2000 to provide a complete count of nesting colonies in the Strait and compare population estimate from counts completed in various years since the mid 1950’s. A complete survey of all colonies was done in 1987. Before that, counts were done in many colonies, though not annually. We surveyed 34 Pelagic Cormorant and 17 Double-crested Cormorant historic and current colonies during the 2000 breeding season. Where possible we examined nest population trends at colonies with multiple years of data. Our analyses showed that overall counts of Pelagic Cormorants were down by half and Double-crested Cormorants had declined by two-thirds since 1987. Pelagic Cormorants showed a significant decline in total nests between 1959 and 2000; although during that period, an increase in the population at Mitlenatch Island was noted. At Double-crested Cormorant colonies, two significant increasing trends were noted. Since 1983 the population at Shoal Islands has slowly increased from zero to 104 nests in 2000. Likewise the population at Mitlenatch has also increased from zero to 70 nests. However these increases do not offset the very dramatic declines in overall population size. The most profound decreases were seen at Mandarte and Great Chain Islands where most of the Double-crested Cormorants were nesting in the late 1980’s. At Mandarte Island, 1100 nests were observed in 1983, while only to 215 were counted in 2000. We suggest that the causes of declines are possibly related to a combination of Bald Eagle disturbance, change in prey availability and human disturbance. Recommendations for management and conservation are discussed.
• The following table is presented in partial form only:
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• “Based on nest counts, the nesting populations of Pelagic and Double-crested Cormorants in the Strait of Georgia have shown alarming declines in the last few years. Concern is especially warranted when one compares the complete counts that were made in 1987 and 2000. The number of nests observed has decreased by 54% for Pelagic and 70% for Double-crested Cormorants. “

• “The populations of both cormorant species have fluctuated considerably over the 40 years of surveys. This could be due to changes in prey availability in the Strait. Cormorants feed on Pacific Herring, Gunnells, Shiner Perch and Salmon. It has been suggested that herring schools have moved north in the Strait of Georgia (Jane Watson, Pers. Comm.), which could account for the increase in both species of cormorants at Mitlenatch. However, this does not account for the loss of the Hornby Island Colony as there is a major herring spawn in that area. As well, it is difficult to explain the increase in the Shoal Islands Double-crested Cormorant colony, by shifts in herring populations.
  Other concerns for nesting cormorants are predation by Bald Eagles (Haliaeetus leucocephalus) and disturbance from boat traffic. Eagle populations have increased on the east side of Vancouver Island (Karen Morrison, Pers. Comm.). Giesbrecht (2001) showed that Eagles were the main source of disturbance to nesting Double-crested Cormorant ’s in the Strait. She observed eagles flushing birds from their nests as well as direct predation on adults/juveniles. Recreational boating and kayaking have also increased in the Strait of Georgia. Although Giesbrecht (2001) did not observe flushing by boaters in her study, anecdotal information (Moul 2001) indicates that human disturbance either by landing at a colony or flushing birds by approaching too closely exposes chicks and eggs to predation by Northwestern Crows (Corvus caurinus), Glaucous-winged Gulls (Larus glaucescens) and Bald Eagles. “

Authors: Shannon S. Badzinski 1, Richard J. Cannings 2, Tasha Smith 2, & Jason Komaromi 3

• Data for two of three species of cormorants show increasing trends (Double-crested
  Cormorant, Pelagic Cormorant). Both these species have shown significant declines in numbers
  at breeding colonies on the British Columbia coast between 1980 and 2000, so the results from
  this survey may indicate a stabilizing trend but further monitoring is clearly needed. Brandt’s
  Cormorants, which occur primarily as a non breeding species, show no clear population trend
  over the past 5 years.