Breeding Biology and Migration Ecology of Turkey Vultures in Western Montana

Abstract

In recent decades, Turkey Vulture (Cathartes aura) populations have both increased and expanded northward in western North America. At our annual fall migration count site in the Bitterroot Valley of western Montana, the number of vultures seen per 100 observation hours more than tripled from an average of 174 birds in the first four years of the count (2011 to 2014) to 581 birds in the last four years (2019 to 2022). Given their recent population growth and expansion in the west, coupled with knowledge gaps in Turkey Vulture breeding biology and migration ecology, we outfitted more than 50 birds with GPS transmitters over the last five years to better understand the western subspecies of Turkey Vulture (C. a. meridionalis). We discuss our early findings from this project, including the timing, distance, and fidelity of migration routes and the difficulty in identifying and locating breeding individuals. We also touch on ecotoxicology and sources of mortality, including the second documented case of a Golden Eagle predating a Turkey Vulture.