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If you've ever felt like a crow was watching you a little too closely, you probably weren't imagining it. Crows are among the smartest animals on the entire planet; these birds have cognitive abilities that rival those of great apes, and even young children.
They're capable of using tools, solving multi-step puzzles and understanding water displacement physics. In fact, they've even been spotted holding what appear to be funerals. However, one of their more astonishing skills is their ability to recognize individual human faces and remember how those people treated them. For years.
The most famous research on crow facial recognition comes from a study, published in 2010 in the journal Animal Behavior, led by Dr. John Marzluff at the University of Washington. Marzluff and his research team wanted to uncover whether or not American crows (Corvus brachyrhynchos) could distinguish between individual humans. More importantly, they also wanted to assess whether they would remember those individuals over time.
The experimental setup was simple but brilliant:
Based on years of data, the research team discovered that the crows' reactions were unmistakably stable over time. They aggressively scolded, mobbed and dive-bombed only the "dangerous" mask -- even when it was worn by a stranger 2.7 years later.
What's more impressive, however, is that, in a 2011 follow-up study published in the Proceedings of the Royal Society B, this behavior was observed to spread to other crows who hadn't witnessed the trapping event. This suggests that crows are capable of social learning: that is, they were actively teaching one other which humans they should hold a grudge against.
However, the surprising part isn't just that the crows could remember individual human faces. Rather, it's how exactly their brains have been wired to do it. Although bird brains are significantly smaller than mammalian ones, they are densely packed with neurons. In particular, corvids (crows, ravens, jays and magpies) have extremely high neuron counts in their forebrains.
In a 2016 study published in the Proceedings of the National Academy of Sciences, neuroanatomical researchers were able to prove that crows have a primate-like nidopallium caudolaterale. Specifically, this is a brain region functionally similar to the mammalian prefrontal cortex, which we use for decision-making, planning and social memory. Most notably, corvids' neuron density is among the highest of any vertebrate of similar size.
During face-recognition tasks, crows have been recorded simultaneously activating their visual processing regions and the parts of their brain associated with emotion and threat assessment. In Marzluff's studies, PET scans showed strong activation in what would be their equivalent of the amygdala when they saw dangerous masks.
This suggests that, for crows, recognizing a human face is both a visual memory task and an emotional one.
Crows are both highly social and long-lived birds. Some species can live from 15 to 20 years in the wild, and many of them mate for life. This means that their survival depends very largely on their ability to cooperate, communicate and understand who can -- and can't -- be trusted. In evolutionary terms, the ability to track individual reputations, friend or foe, confers massive evolutionary advantages.
This ability appears to serve several important functions:
One of the most striking findings from the Washington studies is how emotional memory seems to work in crows. That is, these birds didn't just hold grudges against those who have harmed them; they also made note of positive and neutral interactions, too. This makes sense, considering that there have been countless documented cases of crows:
An especially fascinating aspect of crow memory is the social dimension. As the abovementioned Proceedings of the Royal Society B study suggests, a crow who recognizes a dangerous person is likely to let other crows in the area know too, even if they weren't necessarily harmed by that individual. This suggests two levels of learning:
To scientists, corvid intelligence challenges long-held assumptions about how complex cognition evolves. Traditionally, large-brained mammals (e.g. primates, dolphins, elephants) were thought to be the "smartest" of animals. But crow intelligence evolved along a completely different neurological pathway.
In this sense, studying corvid intelligence may help scientists understand:
So, if you encounter a crow on your morning walk, it's likely already decided whether or not it trusts you. And if it hasn't yet, you're making your first impression every time. Crows are watching. They are remembering. But they are also understanding -- who you are, what you've done and whether you matter to them. And if you're lucky, one might even bring you a shiny gift someday.
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