Given that it is most active at dawn and dusk and has a highly-clumped colonial breeding distribution, the Black-crowned Night Heron is not ideally suited for monitoring by the Breeding Bird Survey (BBS). Nevertheless, moderately precise, range-wide results are available from the survey. BBS results suggest a 40% decrease in abundance relative to the 1970s in Canada. The two Bird Conservation Regions with reasonably reliable results show less severe decreases than the national trend estimates, suggesting that there is regional variation in results (see below). Additional information from the Great Lakes Decadal Colonial Waterbird Census suggests that this population has changed little overall relative to 1970 (~1,800 breeders at 13 colonies in the mid-1970s to ~2,200 breeders at 54 colonies in the late 2000s). BBS results for North America also indicate a slight decline but little overall change. In sum, despite some regional variation, which may account for the discrepancies in survey results, the Canadian population appears to have decreased moderately since 1970. Given these discrepancies though, this assessment has been assigned medium reliability. The Black-crowned Night Heron is below the lowest acceptable level relative to its national population goal (see BBS Canada graph below).
Additional information on: Breeding Bird Survey (BBS) - Canadian analysis
Additional information on: Great Lakes Decadal Colonial Waterbird Census
