The Pacific or Great Blue Heron fannini subspecies winters and breeds on Vancouver Island, B.C. in locations within 5 km of the marine shoreline. Its visibility and close connection to the Salish Sea make it an important flagship species. Due to population concerns and threats associated with urban development, the British Columbia Ministry of Forests, Lands and Natural Resource Operations (FLNRO) biologist (formerly B.C. Ministry of Environment staff) has coordinated monitoring of Pacific Great Blue Heron colonies on Vancouver Island and the adjacent Gulf Islands from 1997 through 2012. Starting in 2005, volunteer stewards and technicians were trained to use a standardized methodology to locate and assess heron colonies, count active nests, determine nest success, and follow a sample of visible nests to determine productivity of young herons that lived until fledgling age.
This report focuses on the 2009 to 2012 breeding seasons (March to September). In each breeding season between 26 and 36 colonies were assessed, and the population variables analyzed to provide indications of Pacific Great Blue Heron population viability. Overall colony success rate ranged from a low of 43% in 2008 to 90% in 2010 with an average of 61%. The number of active nests in the study area did not show a significant trend with a mean of 525 + 14 active nests annually. Nest success in sampled nests ranged from a low of 51% in 2011 to 92% in 2012 with an overall average of 73% + 9%. Vennesland and Butler (2008 COSEWIC report) estimated that at least 63% of active nests would need to fledge young to maintain Pacific Great Blue Heron populations. This occurred in three out of four years during the study period. As well, the average annual productivity on Vancouver Island was 1.5 chicks per sampled nest. In the four years reported here, only in 2010 and 2012 did fledgling productivity exceeded the 1.9 chicks per nest needed to maintain population threshold estimated by Henny and Bethers (1971). Bald Eagle predation on chicks and adults appeared to be responsible for lower productivity, reduced nest success, and colony failures. Another factor in the annual variation of nesting success appeared to be cool wet spring weather, which affected egg production and timing of nesting. Additionally, Pacific Great Blue Heron colonies on Vancouver Island appeared to be locating closer to urban centres, possibly to deter Bald Eagle predation, but this potentially increases heron vulnerability to disturbance from noise, tree cutting, and various other urban development pressures.
This report recommends continued monitoring of the Pacific Great Blue Heron colonies on Vancouver Island and neighbouring Gulf Islands. Additional recommendations include continued distribution of data to local governments and installation of a heron webcam at a well-established colony for public education and outreach purposes. Management issues, including housing developments and tree cutting are ongoing concerns in fast urbanizing areas that overlap with some heron colonies. Low productivity combined with the development pressures make Pacific Great Blue Herons a priority for ongoing protection and monitoring on Vancouver Island.
Chatwin, Trudy, Trudy Chatwin, Emily Barnewall, Ruth Joy, Sharon Ringel, and Heather McCubbin. 2016. Pacific Great Blue Heron Population and Monitoring Vancouver Island and the Gulf Islands 2009 to 2012. Province of British Columbia, Ministry of Forests, Lands and Natural Resource Operations. Wildlife Working Report. WR121