The Breeding Bird Survey (BBS) provides the best long-term national-scale picture of Great Blue Heron trends, and suggests a decrease of about 30% in the Canadian population since about 1970. BBS results have high precision and provide good coverage of the breeding population for this very recognizable species. BBS results vary among the various Bird Conservation Regions that host the species and for which there are reasonably reliable results (displayed below). Other regional results also differ slightly: results from the Great Lakes Decadal Colonial Waterbird Census suggest little overall change since the late 1970s, as do shorter-term results from the British Columbia Coastal Waterbird Survey, which fall under the "little change" category despite showing a slight decline. Interestingly, BBS results at the continental scale show a moderate increase. Overall though, despite some regional variability, the species appears to have undergone a moderate decrease in abundance in Canada since the 1970s. The Great Blue Heron, which includes all subspecies except the fannini subspecies, is currently below the lowest acceptable level relative to its national population goal (see Canada BBS graph below).
Results from targeted nest productivity studies for the fannini subspecies in coastal British Columbia have shown a 50% decline since the 1970s (COSEWIC 2008g). This decline intensified through 1987-2009, particularly at the largest colonies that produce the most young (Environment Canada 2016e). Results from the BBS for British Columbia corroborate these results, showing large decreases in that population. A short-term trend assessment of colony sites on the Gulf Islands and southern Vancouver Island (2002-2015) indicates that the total number of nests was stable, but with low productivity, indicating this population is likely being supplemented by immigration from colonies in the Fraser Valley (Chatwin et al. 2017). The national goal for the fannini subspecies is consistent with the management objective, which is to ensure a stable or increasing population in coastal British Columbia (Environment Canada 2016e); the subspecies is currently below that goal (see BBS graph for the Northern Pacific Rainforest below).
Additional information on: Breeding Bird Survey (BBS) - Canadian analysis
Additional information on: British Columbia Coastal Waterbird Survey
Additional information on: Great Lakes Decadal Colonial Waterbird Census
