Ravens carry food to secret locations, to be eaten later during periods of food shortages

The incomparable raven: World’s second smartest creature?

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Thursday, December 12, 2013 - 12:45am
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Common Raven (Corvus corax) at the Grand Canyon in Arizona. (Photo by Dick Daniels)

One morning in the spring of 2012, friends Jenny and Steve were preparing to leave their Dexter home for work when their dog began barking. Steve looked out to where the dog was chained near the garage and saw a raven standing at the end of the driveway, five feet from the frantic dog. Sensing something unusual was unfolding, Steve called over his wife and they watched the standoff from inside the kitchen. While the raven stood stock-still near the dog, the couple noticed a second raven fly behind the agitated pet. The bird landed briefly on the garage roof before silently gliding to the ground where it quickly ate half of the dog’s food. After a few minutes, the satiated raven flew to the end of the driveway to replace its mate and occupy the dog’s attention, while its mate appeared like a magician at the bowl of dog food. Full of hijacked kibble, the ravens then flew over a potato field. The dog quietly retreated to an empty bowl. As Steve related, “My dog had the perplexed look of a victim just discovering that he’d been pick-pocketed.”

Ravens are famously mischievous and seem to relish playing pranks on dogs. They steal food from raccoons, bears, and sled dogs, drop rocks onto metal roofs, clown around by flying upside down, tug on coyote tails, and mimic human speech. Every wildlife biologist who has worked in northern Maine has a favorite raven story.

Mine happened in March 1989. To observe a rare golden eagle that had been sighted near Baxter State Park, I dumped a horse carcass in a gravel pit next to the Telos logging road. For three days I watched in vain for the eagle, hopeful that it might be attracted to an easy meal. Instead, five ravens flew over the carcass daily. The large black birds with four-foot wingspans called constantly without landing. On the fourth day, with the aid of a spotting scope from my blind a mile away, I watched a pack of coyotes tear open the dead horse. The ravens immediately landed next to the coyotes and acted jittery for ten minutes before finally grabbing bites of horsemeat and quickly retreating. It was a classic ecology textbook example of two species working cooperatively to benefit each other. By squawking constantly above the dead horse, the ravens had recruited the carnivores to do the hard work for them. With their powerful jaws and sharp canines, coyotes easily ripped apart the carcass, making the meat accessible to the ravens.

Mutualism was never more beautiful or explicit. Predators that unintentionally provide ravens with food are unpredictable and dangerous. To avoid being killed, the skittish ravens first gauged the coyotes’ tolerance limits. I watched a raven tug the tail of a coyote pre-occupied with eating horsemeat. Tail-tugging is risky behavior, but it provides the birds with survival information about the capabilities of the coyotes. By intentionally provoking predators, ravens learn which animals they can trust and the location of the proverbial line in the sand.

Throughout history there are numerous stories documenting the close relationships among ravens, wolves and humans. New England ecologist Bernd Heinrich, author of numerous natural history books, has studied ravens for many years near his cabin in western Maine. According to Heinrich, “Humans and ravens have a long common history in a symbiotic relationship, that was severed recently, but we still see remnants of it—though not to the previous extent.”

The raven has been a powerful symbol and a popular subject of mythology and folklore. In the Bible, the raven was the first animal to be released from Noah's Ark. In Norse mythology, a pair of ravens named Huginn (from Old Norse "thought") and Muninn (Old Norse for "memory") flew the world over and brought back information to the god Odin. One raven perched on Odin’s right shoulder; the other on the left, and they took turns whispering information gathered during their travels into Odin’s ears.

Ravens, like the first humans, scavenge on kills of coyotes, wolves, mountain lions, and other carnivores. Heinrich theorizes that ravens learned that wolves, and later humans, would lead them to food. Although ravens are opportunists and omnivores who occasionally hunt independently, they depend primarily on food that others have killed. As large predator populations decline worldwide, ravens are learning to reestablish their ancient alliance with humankind.

In recent years, there’s growing anecdotal evidence that ravens are learning that the sound of gunfire may translate to fast food. My brother Robert lives and hunts big game animals in British Columbia. A few winters ago, he shot a mountain goat and then lost sight of it during a whiteout atop a mountain.  When the skies cleared, he unsuccessfully searched for the dead goat for two hours. Dejected, he was leaving the site when a pair of ravens called overhead before veering off toward a small peak he hadn’t investigated. The birds flew back to him before flying again toward the peak.  Feeling that the ravens might be communicating with him, my brother trudged through knee-deep snow to the summit and found the dead goat. He’s convinced the ravens led him to the goat knowing that once the animal was gutted, they’d be able to eat the viscera.  Robert field-dressed the animal, packed the butchered goat meat on a metal frame, and began his descent back to his truck.  Halfway down the slope, he paused to look uphill with binoculars and indeed saw the ravens feeding on the goat’s internal organs. 

Ravens have closely observed humans because it’s profitable. In the minds of ravens, where humans reside, food is nearby. Earlier in our evolution, humans paid very close attention to ravens. Even today, Inuit hunters scan the arctic skies for ravens, as their ancestors did, believing that the birds dip their wings in the direction of the most productive hunting grounds of caribou, polar bears, and seals. In 1988 ravens led me to ten dead deer in a deer wintering area by vocalizing in the snow-covered woods north of Moosehead Lake. After finding a few dead deer by happenstance, I found the others by paying close attention to the ravens. What was in it for the ravens? My crude field necropsies of the dead deer broke open frozen carcasses, making previously inaccessible deer meat available to the birds.

Ravens also use foresight by carrying food to secret locations, to be eaten later during periods of food shortages. Caching food is a way of putting resources into a rainy day account. Ravens, like most birds, have poorly developed olfactory senses. But they more than make up for this shortcoming by having a photographic memory of hundreds of food caches. Raven memory is far superior to humans, because they have an innate biological advantage. Raven’s re-grow brain cells each year in the hippocampus, the part of the brain responsible for spatial memory, to help them remember new food locations. (Ravens aren’t the only birds with this remarkable adaptation. Each fall, black-capped chickadees grown new brain neurons to also remember hundreds of new food caches.)

All species must constantly adapt to a changing world or perish. Ravens, perhaps more so than others, rely on ingenuity and cleverness to adapt to life in urban and wilderness regions throughout their northern hemisphere breeding range. Their high intelligence is due in large part to an insatiable curiosity to probe and learn everything about their surroundings, from deserts in North America to mountains of Central America. There’s much to learn about ravens—such as why some line their nest with Christmas tree tinsel and stainless steel tire pressure gauges—but science is finally acknowledging that the raven’s IQ may be on par with that of dolphins, elephants, whales, and the great apes. Some scientists claim that ravens are the world's second smartest creature. If they aren’t, then ravens are at least smart enough to have tricked some of humankind’s brightest minds.

 

Ron Joseph is a retired Maine wildlife biologist and lives in Camden.


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