John Marzluff, Ph.D.

John M. Marzluff Ph.D.

Avian Einsteins

Crows Have Opinions

We are not alone in believing about things we can only infer.

Posted Nov 28, 2012

Many of our beliefs are built upon faith in unseen causal agents. Whether you believe God, a raven, or natural selection created humans you do so without having actually seen the creator sculpt a single human. It turns out we are not alone in believing about things we can only infer. And, we are not even the only beings that think about things we cannot see. Reasoning about unseen causal agents also occurs in crows. 

Alex Taylor, Rachael Miller, and Russell Gray have spent many summers on the small island of Maré, New Caledonia. Isolated in the south Pacific, 1100 miles northwest from their home port of Auckland, New Zealand, these researchers study the incredible New Caledonian crow (Corvus moneduloides). In the past, professor Gray and his students have introduced the world to the remarkable tool-making abilities of these crows. Now, in a new paper in the Proceedings of the National Academy of Sciences (, they show us that crows understand “hidden causal agents.”

Demonstrating beliefs by another species requires clever experimentation. In a simple aviary on Maré, researchers watched crows use wooden tools to extract food from within a rectangular, plastic box. To get the food the crows had to bend over and probe the stick deep within the prone box.  Once they learned to do this (no big deal for these tool manufacturing Einsteins), a pair of researchers walked into the aviary. One remained in the far corner with crossed arms and closed eyes while the second person entered a hide that was attached to one end of the crow’s cage. While the person was in the hide a remotely triggered stick came out of the hide toward the food in such a manner than if the crow was in the act of grubbing for a meal it would be wacked in the head by the moving stick. No crows were actually hit, but they were allowed to watch the stick come in and out of the hide 15 times while a person was ensconced. The crows also were able to watch the hidden researcher leave the blind and both researchers exit the aviary.

Now for the clever trick. A person did not have to walk into the hide to trigger the moving stick.  Instead, in half the trials only one person walked into the aviary and stood in the far corner. Nobody entered the hide. Still, the stick probed in and out from the blind toward the food. And after the stick had moved the requisite 15 times, the single person left the crow’s cage. In this condition, the crows were left to ponder what caused the stick to move. Would they believe the stick’s action revealed the presence of something in the blind that they had not seen, and that was presumed to still be hiding?  You bet! Crows that witnessed the stick moving in association with a researcher entering and leaving the hide returned to forage with little concern. But those that only witnessed the stick moving and never saw a person enter or leave the hide were extremely hesitant to pick up a tool and probe for food. Go to the PNAS website I linked above, search for “Taylor crow,” take the link to "supporting information," and watch the associated movie that shows this hesitation. What you are watching is faith in action.  The hesitant crow is thinking about things it cannot see. It is reasoning and acting on its belief.

Anecdotes, mostly from frustrated crow hunters, suggest that other crows also believe. Reports of crows not coming within shooting range of hidden hunters are frequent. In fact, many hunters have told me that crows carefully count hunters entering and leaving a hide (hunting blind) and only return to the vicinity after every hunter that has entered the hide leaves the hide. Tony and I describe one particularly well documented example of this in our book, Gifts of the Crow.

My dictionary defines “belief” as trust, confidence, conviction, or opinion. I believe all of these words describe what a simple crow on an isolated island has demonstrated to scientists. I especially like the last term. I always felt that crows had opinions, now I have proof! Opinions help crows survive the dangers in their world. The adaptive value of opinions—they allow a dangerous predator or situation to be inferred from simple cues or likely scenarios—suggests to me that beliefs may be widespread in the animal kingdom. They are part of our heritage, rather than something we humans alone are capable of devising.

About the Authors

John Marzluff, Ph.D.

John Marzluff, Ph.D. is a professor of wildlife science at the University of Washington where he researches the behavior and conservation of birds, especially crows, ravens, and jays.

Tony Angell

Tony Angell, author and artist, has written and illustrated more than a dozen books and numerous articles and essays related to natural history.

More Posts