For decades, scientists assumed they knew how ravens always managed to show up at a wolf kill before the blood had even dried. The birds must be following the wolves, they had long assumed.
That assumption has now been debunked and replaced with something far more intriguing.
A new research study based on tracking ravens and wolves in Yellowstone National Park over two and a half years shows that ravens use spatial memory to find food, returning from long distances to areas where wolf kills are most likely to occur.
The study, published in the journal Science, was led by the Research Institute of Wildlife Ecology at the University of Veterinary Medicine Vienna and the Max Planck Institute of Animal Behaviour in Germany.
HOW DO RAVENS FOLLOW WOLVES?
The team attached tiny GPS tracking devices to 69 ravens, “which is just an insane number,” said Dr Matthias Loretto, the study’s first author.
Along with the ravens, monitoring movement data was also collected from 20 of Yellowstone’s GPS-collared wolves over winter months.
The data included recorded locations at intervals of up to 30 minutes for ravens and up to one hour for wolves.
What they found surprised them. Over two and a half years of tracking, researchers found only one clear case of a raven following a wolf for more than one kilometre or more than an hour.
“At first, we were puzzled,” said Loretto. “Once we realised that ravens are not following wolves over long distances, we couldn’t explain why the birds still arrive so quickly at wolf kills.”
The answer, it turned out, had less to do with stalking and more associated with memory.
Rather than tracking predators directly, ravens repeatedly revisited specific areas where wolf kills were historically common, like flat valley bottoms where wolves hunt more successfully.
Some ravens flew up to 155 kilometres in a single day, toward places where a carcass was likely to appear, even though the exact timing of a kill is unpredictable.
“We already knew that ravens can remember stable food sources, like landfills,” said Loretto. “What surprised us is that they also seem to learn in which areas wolf kills are more common. A single kill is unpredictable, but over time some parts of the landscape are more productive than others — and ravens appear to use that pattern to their advantage.”
HOW DOES IT MATTER?
The study reframes how scientists think about scavenger behaviour more broadly.
“What our study clearly shows is that ravens are flexible in where they decide to feed. They don’t stay tied to a particular wolf pack. With their sharp senses and memory of past feeding locations, they can choose among many foraging opportunities far and wide,” said senior author John M Marzluff of the University of Washington.
“This changes how we think about how scavengers find food — and suggests we may have underestimated some species for a long time.”
