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The clever, amazing behaviors of crows

American Crow, one of North America’s most widespread bird species, is also one of its smartest.
American Crow, one of North America’s most widespread bird species, is also one of its smartest. Photo by Nancy Bauer/Shutterstock

In my last column, I described how mistakes made by neurobiologists in the late 1890s were perpetuated for about a hundred years, leading to a great misunderstanding of the bird brain. The structural arrangement of the bird brain is very different from that of mammals. This led early biologists to believe that while birds could exhibit simple instinctive behavior, they lacked the ability for cognitive thought.

In the early 2000s, biologists published a major paper correcting this wrong with new information. Importantly, bird brains have many brain cells (neurons) — even more than in mammal brains — packed together and capable of cognitive thought. The most intelligent birds are members of the Corvidae family (crows, ravens, jays, and relatives) and large parrots, all of which have relatively large brains and compare favorably with non-human primates.

With this in mind, imagine a thirsty crow searching for water. After spotting a pitcher on the ground, the crow examines it and sees water inside but out of reach. The crow picks up small stones, dropping them into the pitcher until the water rises high enough to be reached by its beak and to drink. This story is one of many fables attributed to Aesop, the Greek slave and storyteller, who composed many animal-related tales, each with a moral, during the sixth century BCE. The moral for this story, “The Crow and the Pitcher,” is often stated as, “Necessity is the mother of invention.” One reason this story is of special interest is that Aesop assigned cognitive thinking to the crow some 2,000 years ago. We’re just beginning to understand avian cognitive thinking now.

Out of curiosity, Christopher Bird, of the University of Cambridge, and Nathan Emery, of Queen Mary University, London, tested this fable in a laboratory. They worked with Rooks rather than crows, as they were not known to be tool-users. The birds were presented with glass cylinders partially filled with water and an out-of-reach worm floating on top. Small stones were scattered around the cylinders. After looking at the system, the Rooks picked up stones and dropped them into the cylinder until they could reach the worms. And when offered both small and larger stones, the birds selected the larger ones. Aesop had it right.

Betty and 007

New Caledonian Crows from the Pacific islands have the largest brain size of all crows and are known to be excellent tool makers. They utilize stems and leaves from particular plants, and by biting and tearing with their beaks, they create “sticks” to trim around a petiole and leaf to form a “rake.” Both tools are used to dig and scrape insects from holes in logs and branches.

The most famous New Caledonian Crow, Betty, was with others in a study of tool selection at Oxford University. The experiment consisted of a vertical cylinder with a pail containing food and a handle. The test offered the birds two tool choices to remove the pail from the cylinder — a straight wire and a second wire with a hook at the end. When Betty took her turn, the wire with the hook was inadvertently missing. After looking the situation over, Betty picked up the straight wire, placed an end in a “corner” and bent the wire with her beak, creating a hook at the end. She reached into the cylinder with the hooked wire, caught the handle, and lifted out the pail containing a lovely snack of pig heart.

Betty received rock-star treatment for using insightful thinking to design a tool on the spot from material she had never handled. Subsequently, biologists observed her species making tools, and about half of them bent the tools to create a hook-like structure. So maybe Betty’s tool was more of a species-specific behavior than a result of great insightful thought.

 Another New Caledonian Crow celebrity, 007, solved an eight-step puzzle designed by Alex Taylor of the University of Auckland. It consisted of three different puzzles that 007 had solved individually. In the room where the experiment was conducted, 007 saw the three puzzles together on a table for the first time. He had to solve eight steps in a sequence to retrieve a meat snack. The meat was visible between two sheets of plexiglass but couldn’t be reached.

He pulled up a string hanging from his perch, with a small stick tied to the end. The small stick was too short to reach the meat but was used to scrape three partially hidden stones from openings in the sides of three small “buildings.” The stones were dropped into a chimney-like structure of another building, and they fell to the floor, which was slightly tilted and hinged with counterweights such that all three stones had to hit the floor in order to tilt it enough to expose a partially hidden longer stick. With the longer stick, he could reach the meat. 007 solved the puzzle in three minutes.

Recognizing threats

Crows are among the most abundant birds in North America. Their cleverness has allowed them not only to tolerate humans but to thrive with human settlements. Crows probably know the paths of garbage trucks in an area better than the residents, and they certainly know which roads to check early in the morning for roadkill. Some people love to have crows around, while others dislike them. Because of this love/hate relationship, it would seem advantageous if they could recognize which humans like them and which don’t.

John Marzluff, of the University of Washington, has studied crows for many years and wondered the same thing. In an experiment, he had a team of seven students trap crows on campus and keep them in an aviary. All students trapping and handling the crows wore identical “caveman” rubber masks that were misshapen and ugly.

After the crows were released, seven students who had not trapped or handled the crows but who wore the caveman masks walked through campus where crows were present and were attacked by crows. More birds attacked them than were originally captured, so the crows apparently communicated about the threat to their flock mates. However, when the students who trapped the birds appeared on campus with a human mask (depicting Dick Cheney), the crows ignored them.

Ten years later, when the experiment was repeated and after some crows had died, students wearing the caveman masks were still attacked. When students wore the masks upside down, crows would tilt their heads to better see them and then attack.

There are many anecdotal stories of crows leaving objects with people who feed them. My favorite began in 2001 with 4-year-old Gabi Mann from Seattle. As she got out of her family car, she dropped a chicken nugget from her lunch. A crow, perched nearby, quickly swooped in, grabbed the nugget, and flew off. Gabi enjoyed this and managed to add more food scraps to her yard from time to time. When Gabi started school, she would save at least part of her lunches to share with crows. When her school bus stopped near her house at day’s end, the yard always had waiting crows. With her mother’s help, Gabi got more organized. They set up a birdbath and regularly put food, especially peanuts, on the edges of the bath.

Early on in this relationship, trinkets started appearing on the bath: beads, buttons, pieces of metal, and plastic; shiny objects were common. Biologists believe that the giving of gifts for food is probably related to courtship behavior.

Gabi’s mother thinks the crows watch over them, describing one day when she was photographing eagles near their home. She accidentally dropped her lens cap but kept going, planning to pick it up later. After returning home, she realized that she forgot to look for her lens cap and decided to go back for it. When she went by the birdbath, the lens cap was sitting on it. It was hers. She went into the house to check her surveillance video and saw a crow bring the lens cap to the bath. Not only did the crow bring it back, it rinsed the cap in the bath several times before leaving it.

With the renewed understanding of avian brain anatomy and function, we will continue to be in awe of those amazing birds.

This article was first published in the “Amazing Birds” column in the September/October 2020 issue of BirdWatching magazine. 

Study: New Caledonian Crows can create compound tools

Researchers discover how crows manufacture hooked tools

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Eldon Greij

Eldon Greij

Eldon Greij (1937-2021) was professor emeritus of biology at Hope College, located in Holland, Michigan, where he taught ornithology and ecology for many years. He was the founding publisher and editor of Birder’s World magazine and the author of our popular column “Those Amazing Birds.”

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