麻豆影视

Perhaps 鈥渂irdbrained鈥� isn鈥檛 such an insult after all 鈥撯�� crows, the ubiquitous urban bird, can vocally count up to four, the latest research has found.

Not only can the inquisitive creatures count, but they can match the number of calls they make when shown a numeral, according to a new study, led by a team of researchers with the University of Tübingen鈥檚 animal physiology lab in Germany.

The way the birds recognize and react to numbers is similar to a process we humans use, both to learn to count as toddlers and quickly recognize how many objects we鈥檙e looking at. The findings, Thursday in the journal Science, deepen our growing understanding of crow intelligence.

鈥淗umans do not have a monopoly on skills such as numerical thinking, abstraction, tool manufacture, and planning ahead,鈥� said animal cognition expert Heather Williams via email. 鈥淣o one should be surprised that crows are 鈥榮mart.鈥欌�� Williams, a professor of biology at Williams College in Massachusetts, was not involved in the study.

In the animal kingdom, counting isn鈥檛 limited to crows. Chimpanzees have been and understand the value of numerals, much like young children. In attempting to woo mates, some male frogs to match or even one-up that number when it鈥檚 their turn to croak at a female. Scientists have even theorized that ants retrace their paths back to their colonies by , though the method isn鈥檛 always accurate.

What this latest study showed is that crows, like young humans, can learn to associate numerals with values 鈥撯�� and count out loud accordingly.

Can crows count much like toddlers do?

The research was inspired by toddlers learning to count, said lead study author Diana Liao, a neurobiologist and senior researcher at the Tübingen lab. Toddlers use the words of numbers to tally the number of objects in front of them: If they see three toys in front of them, their counting could sound like 鈥渙ne, two, three鈥� or 鈥渙ne, one, one.鈥�

Maybe crows could do the same, Liao thought. She was inspired, too, by a June 2005 study on chickadees tailoring their alarm calls to a predator鈥檚 size. The larger a predator鈥檚 wingspan or body length, the fewer 鈥渄ee鈥� sounds the chickadees used in their alarm call, the study . The opposite was true for smaller predators 鈥撯�� the songbirds would use more 鈥渄ee鈥� sounds if they encountered a smaller bird, which could be greater threats to chickadees since they are more agile, Liao said.

The authors of the chickadee study couldn鈥檛 confirm whether the small songbirds had control over the number of sounds they made or if the number of sounds were an involuntary response. But the possibility piqued Liao鈥檚 curiosity 鈥撯�� 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 鈥渃ounting鈥� like toddlers do?

The crows planned their number of caws

Liao and her colleagues trained three carrion crows, a European species closely related to the American crow, over more than 160 sessions. During the trainings, the birds had to learn associations between a series of visual and auditory cues from 1 to 4 and produce the corresponding number of caws. In the example researchers provided, a visual cue might look like a bright blue numeral, and its corresponding audio could be the half-second song of a drumroll.

The crows were expected to perform the same number of caws as the number represented by the cue 鈥撯�� three caws for the cue with the numeral 3 鈥撯�� within 10 seconds of seeing and hearing the cue. When the birds had stopped counting and cawing, they would peck at an 鈥渆nter鈥� key on the touchscreen that presented their cues to confirm that they were done. If the birds had counted correctly, they鈥檇 receive a treat.

It appeared that as the cues continued, the crows took longer to react to each cue. Their reaction times grew as 鈥渕ore vocalizations were impending,鈥� Liao wrote, suggesting that the crows planned the number of caws they were going to make before they opened their beaks.

The researchers could even tell how many calls the birds planned to make by the way their first call sounded 鈥撯�� subtle acoustic differences that showed that the crows knew how many numbers they were looking at and had synthesized the information.

鈥淭hey understand abstract numbers 鈥� and then plan ahead as they match their behavior to match that number,鈥� Williams said.

Even the mistakes the crows made were somewhat advanced: If the crows had cawed one too many times, stuttered over the same number or submitted their responses with their beak prematurely, Liao and her researchers could detect from the sound of the first call where they went wrong. These are the 鈥渟ame kinds of errors humans make,鈥� Williams said.

We鈥檙e still learning how smart crows are

Birds and many other animals were previously thought to make only on-the-spot decisions based on stimuli in their immediate environments, a theory popularized by the 20th century animal behaviorist B.F. Skinner. But the latest research by Liao and her colleagues provides more evidence about crows鈥� ability to synthesize numbers to produce a sound and suggests that the skill is within their control.

The study team鈥檚 findings are highly specific but still significant 鈥撯�� they challenge the once common belief that all animals are merely stimulus-response machines, said Kevin McGowan, a researcher at the Cornell Lab of Ornithology in Ithaca, New York, who has spent more than two decades studying wild crows in their habitats. McGowan wasn鈥檛 involved in the study.

The study, McGowan told CNN, demonstrated that 鈥渃rows aren鈥檛 just simple nonthinking machines out there reacting to their environment 鈥撯�� they鈥檙e actually thinking ahead and have the ability to communicate in a structured, preplanned way. It鈥檚 sort of a necessary precursor for having a language.鈥�

has been studied for decades. Scientists have investigated New Caledonian crows to access food. The birds appear to establish rules, according to a coauthored by the University of Tübingen lab鈥檚 lead researcher, Andreas Nieder. Crow language has confounded scientists for decades, too, with its widely varying tones and expressions, McGowan said.

The study by Liao and her colleagues isn鈥檛 even the first to consider whether crows can count. That research began with Nicholas Thompson in 1968, animal cognition expert Irene Pepperberg noted. A research professor of psychological and brain sciences at Boston University, Pepperberg is best known for her work with an African grey parrot named Alex.

Thompson hypothesized that crows could count based on their caws, the duration and number of which the birds appeared to control in a given burst of sound. The crows鈥� counting abilities 鈥渟eem to exceed the demands which survival makes for such abilities,鈥� he wrote.

Another University of Tübingen from September 2015 trained the birds to recognize groupings of dots and recorded the activity of neurons in the part of the crows鈥� brains that receives and makes sense of visual stimuli. The researchers found that the crows鈥� neurons 鈥渋gnore the dots鈥� size, shape and arrangement and only extract their number,鈥� the university in a statement at the time.

鈥淪o, crows鈥� brains can represent different quantities, and crows can quickly learn to match Arabic numerals to those quantities 鈥撯�� something humans usually explicitly teach their children,鈥� Williams said.