Characterizing juvenile dispersal dynamics of invasive Barred Owls: Implications for management

Characterizing natal dispersal can help manage the spread of invasive species expanding their ranges in response to land use and climate change. The Barred Owl (Strix varia) is a prominent example of an apex predator undergoing a rapid range expansion, having spread from eastern to western North America where it is now hyperabundant-threatening the Northern Spotted Owl (Strix occidentalis caurina) with extinction and potentially endangering many other native species. We attached satellite tags to 31 Barred Owl juveniles at the southern leading edge of the Barred Owl's expanding range in California to characterize natal dispersal patterns and inform management. Juveniles traveled up to 100 km from natal territories and experienced high mortality (annual survival = 0.204). At landscape scales, juveniles preferentially used forests, shrublands, and lower elevations during dispersal and avoided grasslands and burned areas. At finer scales, juveniles preferred shorter (younger) forests, lower elevations, and drainages, and avoided unforested areas. Our results suggest that the Barred Owl range expansion is being driven primarily by high reproductive rates and densities despite low juvenile survival rates and dispersal through putatively suboptimal younger forests as a result of exclusion from high-quality habitat by territorial individuals. These findings also point to several strategies for conserving Spotted Owls and other native species in the Barred Owl's expanded range, including: (1) creating and maintaining Barred Owl-free reserves bounded by open or high elevation areas, (2) creating reserves large enough to reduce immigration by long-distance dispersers, and (3) removing Barred Owls from large riparian corridors. center dot Juvenile movement is a major driver of range expansion in wildlife species.center dot Barred Owl range expansion into North America has negatively affected native species like the Spotted Owl.center dot We tracked juvenile Barred Owls in coastal California with satellite GPS tags.center dot Juveniles showed long dispersal (up to 100 km) and low annual survival (0.2).center dot Juveniles selected young forest and riparian areas, avoiding grass and burned areas.center dot Barred Owl invasion was likely facilitated by many offspring and long-distance juvenile dispersal.center dot Large open areas and removal in riparian corridors may limit Barred Owl spread and facilitate Spotted Owl conservation. Caracterizar la dispersion natal puede ayudar a gestionar la propagacion de especies invasoras que expanden sus rangos en respuesta al uso del suelo y al cambio climatico. Strix varia es un ejemplo destacado de un depredador tope que experimenta una rapida expansion de su rango, habiendose extendido del este al oeste de America del Norte, donde ahora es hiper abundante, amenazando de extincion a S. occidentalis caurina y potencialmente poniendo en peligro muchas otras especies nativas. Colocamos marcadores satelitales a 31 juveniles de S. varia en el extremo sur del rango en expansion en California de S. varia para caracterizar los patrones de dispersion natal e informar sobre la gestion. Los juveniles viajaron hasta 100 km desde sus territorios natales y experimentaron una alta mortalidad (supervivencia anual = 0.204). A las escalas de paisaje, los juveniles utilizaron preferentemente bosques, matorrales y elevaciones mas bajas durante la dispersion, evitando areas de pastizales y quemadas. A escalas mas finas, los juveniles prefirieron bosques mas bajos (mas jovenes), elevaciones mas bajas y drenajes, y evitaron areas sin bosque. Nuestros resultados sugieren que la expansion del rango de S. varia esta siendo impulsada principalmente por altas tasas de reproduccion y densidades elevadas, a pesar de las bajas tasas de supervivencia juvenil y la dispersion a traves de bosques mas jovenes aparentemente sub-optimos, como resultado de la exclusion de habitats de alta calidad por parte de individuos territoriales. Estos hallazgos tambien senalan varias estrategias para conservar a S. occidentalis caurina y otras especies nativas en el area de expansion de S. varia, incluyendo: (1) crear y mantener reservas libres de S. varia delimitadas por areas abiertas o de alta elevacion; (2) crear reservas lo suficientemente grandes como para reducir la inmigracion de dispersores de larga distancia; y (3) remover a los individuos de S. varia de grandes corredores riberenos.