2025/09/26 by Justine Le Vaillant, Alexandre Terrigeol, Laetitia Desbordes +11 · 1 voice
Environmental Science · #Ecology and Vegetation Dynamics Studies #Species Distribution and Climate Change #Rangeland and Wildlife Management
paper · doi:10.1080/15594491.2025.2547332
Many boreal species have declined during recent decades in North America. Various indexes suggest that populations of the Boreal Owl Aegolius funereus are declining across North America, but very few long-term, standardized monitoring schemes allow for reliable assessment. We combined various datasets monitoring Boreal Owls in eastern North America to assess its population trend. Using autumn migration monitoring from 1996 to 2023 at Tadoussac (Québec, Canada) and Whitefish Point (Michigan, USA), we assessed population trends with Bayesian hierarchical generalized linear models. We also analyzed the trends in the proportion of juveniles and body condition over time. We correlated migration monitoring with participatory science observations recorded throughout the year to assess Boreal Owl population trends in eastern North America. We observed a dynamic of four-year cycles and a longer-term decline in relative abundance for both the total number of captured individuals and the number of juveniles alone. The proportion of juveniles and mean body condition both varied annually but showed stable trends over time. However, we detected a reduction in the recorded fat score over time, suggesting that conditions encountered in the boreal forest could be deteriorating. This study provides population trends for the Boreal Owl, an important bioindicator of the boreal ecosystem, and could ultimately support and orient the development of future monitoring projects during the breeding period.