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1. Top predators have cascading effects throughout the food web but their
impacts on scavenger abundance are largely unknown. Gray wolves (Canis
lupus) provide carrion to a suite of scavenger species, including the
common raven (Corvus corax). Ravens are wide-ranging and intelligent
omnivores that commonly take advantage of anthropogenic food resources. In
areas where they overlap with wolves, however, ravens are numerous and
ubiquitous scavengers of wolf-acquired carrion. 2. We aimed to determine
whether subsidies provided through wolves are a limiting factor for raven
populations in general and how the wolf reintroduction to Yellowstone
National Park in 1995-1997 affected raven population abundance and
distribution on the Yellowstone’s Northern Range specifically. 3. We
counted ravens throughout Yellowstone’s Northern Range in March from 2009
to 2017 in both human-use areas and wolf habitat. We then used statistics
related to the local wolf population and the winter weather conditions to
model raven abundance during our study period and predict raven abundance
on the Northern Range both before and after the wolf reintroduction. 4. In
relatively severe winters with greater snowpack, raven abundance increased
in areas of human use and decreased in wolf habitat. When wolves were able
to acquire more carrion, however, ravens increased in wolf habitat and
decreased in areas with anthropogenic resources. Raven populations prior
to the wolf reintroduction were likely more variable and heavily dependent
on ungulate winter-kill and hunter-provided carcasses. 5. The wolf
recovery in Yellowstone helped stabilize raven populations by providing a
regular food supply, regardless of winter severity. This stabilization has
important implications for effective land management as wolves recolonize
the west and global climate patterns change.
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