Maybe “birdhead” isn’t such an insult after all –– crows, the ubiquitous urban birds, can vocally count to four, according to recent research.
Not only can these curious creatures count, they can also match the number of calls they make when they see a numeral, according to the study, led by a team of researchers from the animal physiology laboratory at the University of Tübingen in Germany.
The way birds recognize and react to numbers is similar to a process we humans use both to learn to count when we are young children and to quickly recognize how many objects we are seeing. The findings, published on Thursday (23) in Science magazinedeepen our growing understanding of crow intelligence.
“Humans do not have a monopoly on skills like numerical thinking, abstraction, tool making, and planning ahead,” said animal cognition expert Heather Williams in an email. “No one should be surprised that crows are ‘smart’.” Williams, who is a biology professor at Williams College in Massachusetts, was not involved in the study.
In the animal kingdom, counting is not limited to crows. Chimpanzees have been taught to count in numerical order and understand the value of numbers, just like young children. In an attempt to win mates, some male frogs count the number of calls from competing males to match or even surpass that number when it is their turn to croak at a female. Scientists even theorize that ants retrace their paths back to their colonies by counting their steps, although the method is not always accurate.
What this latest study has shown is that crows, like young humans, can learn to associate numbers with values –– and count out loud.
Can crows count the same way as little children?
The research was inspired by young children learning to count, said study lead author Diana Liao, a neurobiologist and senior researcher at the Tübingen laboratory. Young children use number words to count the number of objects in front of them: If they see three toys in front of them, their count may sound like “one, two, three” or “one, one, one.”
Maybe crows could do the same, Liao thought. She was also inspired by a June 2005 study of chickadees (a species of bird) that adjusted their alarm calls according to the size of the predator. The greater the wingspan or body length of a predator, the fewer “dee” sounds the birds used in their alarm call, the study found. The opposite was true for smaller predators –– the birds would use more “dee” sounds if they encountered a smaller bird, which could be a greater threat since they are more agile, Liao said.
The authors of the chickadee study could not confirm whether the small birds had control over the number of sounds they made or whether the number of sounds was an involuntary response. But the possibility piqued Liao’s curiosity –– could crows, whose intelligence has been well documented over decades of research, show control over their ability to produce a certain number of sounds, effectively “counting” as young children do?
Crows planned their number of screams
Liao and his colleagues trained three crows of the species corvus corone, a European species closely related to the American crow, during more than 160 sessions. During training, the birds had to learn associations between a series of visual and auditory signals from 1 to 4 and produce the corresponding number of cries. In the example provided by the researchers, a visual signal could look like a bright blue numeral, and its corresponding audio could be the half-second sound of a drum roll.
Crows were expected to perform the same number of calls as the number represented by the sign –– three calls for the sign with the numeral 3 –– within 10 seconds of seeing and hearing the sign. When the birds stopped counting and shouting, they pecked an “enter” key on the touchscreen that displayed their signals to confirm they were finished. If the birds counted correctly, they received a reward.
It seemed that as the signals continued, the crows took longer to react to each signal. Their reaction times increased as “more vocalizations were to come,” Liao wrote, suggesting that the crows planned the number of calls they would make before opening their beaks.
The researchers could even tell how many calls the birds planned to make by the way the first call sounded –– subtle acoustic differences that showed that the crows knew how many numbers they were seeing and had synthesized the information.
“They understand abstract numbers…and then plan ahead while adjusting their behavior to match that number,” Williams said.
Even the mistakes the crows made were somewhat advanced: If the crows called one too many times, stuttered over the same number, or submitted their beak responses prematurely, Liao and his researchers could detect from the sound of the first call where they went wrong. These are the “same types of mistakes that humans make,” Williams said.
We’re still learning how smart crows are
Birds and many other animals were previously believed to make decisions only in the moment, based on stimuli in their immediate environments, a theory popularized by 20th-century animal behaviorist BF Skinner. But the latest research by Liao and his colleagues provides more evidence about crows’ ability to synthesize numbers to produce a sound and suggests that this ability is within their control.
The study team’s findings are highly specific but still significant –– they challenge the common belief that all animals are merely stimulus-response machines, said Kevin McGowan, a researcher at the Cornell Laboratory of Ornithology in Ithaca, New York, who has studied wild crows in their habitats for more than two decades. McGowan was not involved in the study.
The study, McGowan told CNN, demonstrated that “crows are not just simple, mindless machines reacting to their environment –– they are actually thinking ahead and have the ability to communicate in a structured, planned way. It’s a kind of necessary precursor to having a language.”
The intelligence of crows has been studied for decades. Scientists have investigated New Caledonian crows creating their own composite tools to access food. Birds appear to set rules, according to a November 2013 study co-written by University of Tübingen laboratory lead researcher Andreas Nieder. Crow language has baffled scientists for decades as well, with its widely varying tones and expressions, McGowan said.
Liao and his colleagues’ study is not the first to consider whether crows can count. This research began with Nicholas Thompson in 1968, noted animal cognition expert Irene Pepperberg. A research professor of psychological and brain sciences at Boston University, Pepperberg is best known for her work with an African gray parrot named Alex.
Thompson hypothesized that crows could count based on their calls, the duration and number of which the birds seemed to control in a given burst of sound. Crows’ counting abilities “appear to exceed the demands that survival makes on such abilities,” he wrote.
Another University of Tübingen study on crows’ counting abilities from September 2015 trained the birds to recognize clusters of dots and recorded the activity of neurons in the part of the crows’ brains that receives and interprets visual stimuli. The researchers found that the crows’ neurons “ignored the size, shape and arrangement of the dots and only extracted their number,” the university said in a statement at the time.
“So crows’ brains can represent different quantities, and crows can quickly learn to match Arabic numerals to these quantities –– something humans often explicitly teach their children,” Williams said.
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