Unveiling 25 Years of Aerial Surveys: Contrasting Trends in Great Blue Heron (Ardea herodias) Nest and Heronry Abundance in Quebec

The Great Blue Heron (Ardea herodias) is an indicator of aquatic ecosystems. Understanding its population trends is vital for gauging ecosystem health. However, trends vary in North America, posing challenges to effective conservation strategies. This study examines the 25-year population trends of Great Blue Herons in Quebec through aerial surveys. Generalized linear models were employed to track nest and heronry abundance, considering bird conservation region (BCR), survey effort, and years. A model selection approach identified the best predictors. The best model for nest abundance, incorporating additive effects of BCR and year, explained 87% of the model selection's weight, revealing a decline across all BCRs from 1992 to 2017. For heronry abundance, two models highlighted the influence of BCR over the years, indicating relative stability in the province. Divergent trends between nest and heronry abundance raise questions about influencing factors. Proposed strategic conservation actions aim to ensure that the most ecologically valuable heronries are properly preserved. This may involve reassessing protection measures and, in some cases, considering restoration actions. This study underscores the challenge of adequately covering large administrative regions, with proposed resolutions including a dual-frame design for future surveys.