Ravens Demonstrate Spatial Memory While Scavenging, Says Yellowstone Study

By studying ravens, gray wolves, and cougars in Yellowstone National Park, researchers discovered that, contrary to common belief, ravens rarely follow predators over long distances and instead rely on spatial memory to return to places where kills have occurred before. The finding is surprising considering that revisiting previous kill sites is more cognitively demanding, as it requires predicting the behavior and space use of another species.

Ravens, a common scavenger, are ideal candidates for testing the idea of spatial memory, as they are known for their advanced cognitive abilities. The study (attached) points out that the future-planning abilities of ravens are similar to those of great apes, which may help them predict the behavior of other scavengers or predators. 

Little is known about raven-cougar interactions, but ravens are the most prominent scavenger species at wolf kills in many regions. In various studies, ravens have been observed flying with traveling wolves, following wolf tracks in the snow, orienting toward wolf howling, and aggregating rapidly at fresh wolf kills.

Over 2.5 years, researchers collected 646,494 locations from 69 ravens, 77,085 locations from 20 wolves, and 58,269 locations from 11 cougars equipped with GPS devices in Yellowstone, or within 5 km of its boundaries. 

The researchers found that ravens were capable of following wolves over considerable distances and extended periods, but it was rare. Over 2.5 years of tracking, they recorded only one instance of this, where a raven and a wolf moved together in the same direction for 4 km over a period of 2 hours.

The study also discovered that a significantly greater proportion of GPS-tagged ravens exploited ungulates killed by wolves than by cougars. This may be due to several factors, including the fact that wolf packs operate in groups and are easier to spot during hunting. They also tend to hunt in open areas and will sometimes howl when initiating a hunt or near a kill. In contrast, cougars kill less frequently, mostly forage alone, cover kills between feedings, and hunt in rugged, forested terrain.

While wolves are significantly easier to follow, ravens, instead of consistently remaining near the carnivores, periodically returned to areas of high carnivore activity or past kill sites, while primarily foraging elsewhere, explained the study.

“Because wolf kills are clustered in particular areas of northern Yellowstone and not randomly distributed, we propose that ravens find kills by relying on spatial memory, possibly represented as a cognitive map of long-term average wolf presence and/or wolf kill abundance,” wrote the researchers.

To test the idea more fully, they created a carcass abundance map based on the total number of recorded wolf kills during the study, aggregated into 3-km grid cells. The proportion of GPS-tagged ravens visiting a wolf kill was significantly higher in grid cells with more wolf kills than in areas where kills were previously rare. This indicates that ravens may learn and remember areas where wolf kills are abundant and where they are not.