This report describes the results of the population inventory and monitoring of Great Blue Heron on Vancouver Island (Region 1) for 2007 and 2008. In 2007, there were 605 active nests, in 33 active colonies and in 2008 there were 506 active nests in 31 active colonies. There was no significant increase or decrease in the number of active heron nests each year on Vancouver Island from 2002 to 2008; however, it appears that the number of colonies is increasing through fragmentation of larger colonies. In 2007, of the 25 colonies with known outcomes 17 (68%) were successful and 8 (32%) were failed colonies. The 2008 breeding year was a relatively unsuccessful year with only 12 (43%) successful colonies and 16 failed (57%) colonies. Many of the failures were attributed to predation by Bald Eagles. In 2008 the larger colonies at Shoal Islands and Clamshell Road on Gabriola as well as many small colonies failed. In addition to overall colony success rate, we monitored fledgling productivity at 67 active sample nests in 2007 and 117 active sample nests in 2008. In 2007 the 67 sample nests fledged 105 young, yielding a mean productivity of 1.70 fledglings per active nest (standard error = 0.35). In 2008 the 117 nests fledged 95 young, yielding a mean productivity of 1.07 fledglings per active nest (standard error = 0.37). As there were total failures of several large colonies in 2008, at least 269 nests of 506 active nests failed. The low fledgling productivity and high rates of colony failure in 2008 suggest a potential for future population declines. Management issues, including housing developments and tree cutting, are ongoing concerns in this fast-urbanizing area. The low productivity combined with the development pressures, make Great Blue Herons a priority for ongoing protection and monitoring.
Chatwin, T., T. Dunlop, R. Joy. 2009. Pacific Great Blue Heron Population and Monitoring Vancouver Island and the Gulf Islands 2007 and 2008. Ministry of Environment. Wildlife Working Report. wr 119