YELLOWSTONE NATIONAL PARK — A new research article that appeared in the journal Science this month found that the relationship between wolves and ravens in Yellowstone National Park (YNP) follows a surprising dynamic.
Ravens, known scavengers, are closely tied to the wolf population in Yellowstone: animals killed by wolves turn into carrion for ravens. Previously, some biologists defaulted to the assumption that ravens were following wolves around, observing their successful hunting endeavors. New research suggests that ravens are not actively following the wolves and waiting for a new kill; instead, they keep track of locations where they’ve found wolf-killed carrion before.
“By satellite tracking 69 ravens, 20 wolves, and 11 cougars in Yellowstone National Park, we found that following of predators over large distances rarely occurred,” the study’s abstract reads. “Instead, ravens routinely revisited sites where wolf kills were common — returning from distances of up to 155 kilometers to find carrion. Much like navigating to permanent anthropogenic subsidies, ravens appear to remember potential sources of carrion shaped by previous encounters with wolves or their kills. These findings suggest that spatial memory and navigation play a considerably greater role than previously assumed among scavengers, and possibly other wide-ranging species, in search of ephemeral resources.”
Fans of Yellowstone ecology will find much food for thought in this new piece. Study authors Matthias-Claudio Loretto, Kristina B. Beck, Douglas W. Smith, Daniel R. Stahler, Lauren E. Walker, Martin Wikelski, Thomas Mueller, Kamran Safi and John M. Marzluff lend new credence to ravens’ “wolf-bird” nickname.
“Overall, 48.5% of the wolf kills and 24.8% of the cougar kills were used by at least one GPS-tagged raven during the first 7 days postmortem,” the study reads. “A significantly greater proportion of GPS-tagged ravens exploited ungulates killed by wolves compared with cougar kills.”
The scientists also pointed out that wolf hunting grounds (and thus raven feeding grounds) tend to be determined by YNP’s unique landscape features, noting that flat, open, snow-covered grasslands near streams and roads are frequently the sites of wolves successfully hunting elk, whereas the rocky terrain favored by mountain lions yields less predictable results.
Also noteworthy: The authors compare the spatial memory awareness in ravens to other examples of “knowledge of a resource landscape” in the animal kingdom, including blue whales’ tracking of spring phytoplankton blooms and chimpanzees revisiting fruit-bearing trees. Read the study here.
