Alarming Decline Puts Endangered Reunion Harrier in "Extinction Vortex"

The Reunion Harrier (Circus maillardi), an endemic bird of prey and the last breeding raptor on La Reunion island in the Indian Ocean, faces a precarious future. Already listed as "endangered" on the IUCN Red List, concerns have mounted recently regarding its survival. Researchers were particularly worried about the demographic impacts of secondary poisoning from anticoagulant rodenticides used in agriculture, alongside other persistent threats such as habitat loss, fragmentation, and reduced genetic diversity.

To assess the true state of the population, a comprehensive analysis was conducted using data from three standardized island-wide breeding censuses spanning 21 years (1998–2000, 2009–2010, 2017–2019). These extensive surveys involved 355 sampling points and over 1,500 hours of observation. The findings were stark: a significant decrease of 46% in the relative abundance of breeding pairs was estimated across the island. The decline was even more pronounced in the eastern part of La Reunion, experiencing a 56% reduction, compared to a 29% decline in the western part.

These alarming results strongly support the harrier's current endangered status. As lead author Villers notes in the paper, "Combined with previous work on inbreeding and mutational load, exposure to anticoagulant rodenticides and ongoing threats (habitat changes), these results suggest this harrier population is undergoing an extinction vortex that requires immediate and targeted, spatially explicit, conservation actions." This critical situation demands sustained attention. Researchers emphasize the importance of continuous monitoring of population size and improving knowledge of demographic parameters to guide effective adaptive management strategies for this unique and threatened species.