This story takes up most of the front page of the "Health & Science" section
of today's Washington Post (page E1)
Title in the paper: "Who you callin' bird brain?" page E1
By Kiona Smith-Strickland
Are crows the smartest animals of all?
Many scientists think that corvids -- the family of birds that includes crows,
ravens, rooks and jays -- may be among the most intelligent animals on Earth,
based on their ability to solve problems, make tools and apparently consider
both possible future events and other individuals' states of mind.
"There's a lot of research that has been done with both ravens and crows because
they are such intelligent species," said Margaret Innes, an assistant curator at
the Maryland Zoo in Baltimore.
Even in humans, defining and measuring intelligence is difficult, and it's more
complicated in other species, which have very different body shapes and have
evolved for their niche in the environment. However, scientists who study
cognition have defined a few measures of intelligence: recognizing oneself in a
mirror, solving complex problems, making tools, using analogies and symbols, and
reasoning about what others are thinking.
For a long time, biologists expected most of these mental feats to be unique to
primates. The great apes -- chimpanzees, orangutans and gorillas -- succeed at
nearly all of these tasks, from making and using tools to learning large
vocabularies of symbols, as well as recognizing themselves in mirrors.
Crows: Smart as your average 7-year-old?
In this study by the University of Auckland and the University of Cambridge,
crows drop objects into tubes filled with water, raising the water level and
obtaining a food reward. Researches found that this species of crows can solve a
science puzzle about as well as the average 7-year-old kid. (University of
Auckland, University of Cambridge)
A select few other mammals also meet most of the accepted criteria for
intelligence. Dogs and dolphins, for instance, are very good at tasks involving
social intelligence, such as communication, conflict resolution and reasoning
about what others are thinking. Dolphins are also capable of basic tool use --
for instance, carrying sea sponges in their mouths to shield their noses from
scrapes and bumps as they forage on the ocean floor.
However, the greatest intellectual rival to the brainy apes may be a noisy
scavenger with a sharp beak, bright eyes and a brain about the size of a walnut:
the crow and its corvid relatives.
Crows and ravens are clever problem-solvers, expert toolmakers and adept social
movers, but scientists haven't reached a consensus about how corvid minds handle
abstract thinking or how closely their mental processes resemble those of
Researchers from the University of Iowa and Lomonosov Moscow State University in
Russia reported <http://www.sciencedirect.com/science/article/pii/S0960982214015577>
early this year that crows can use analogies to match pairs of objects. To reach
that conclusion, the scientists trained crows to recognize whether two objects
were identical or different, which the birds indicated by pressing one button
when shown pictures of objects that matched and a different button when the
objects didn't match. Once all the birds were good at matching objects,
researchers showed the crows images of pairs of objects. Some images depicted
matched pairs, while others depicted two mismatched objects with different
shapes or colors. In response, crows could press buttons to choose between a
matched pair or a mismatched pair.
The researchers wanted to see if crows could figure out the relationship between
pairs of objects and then choose a pair with the same relationship: matched or
mismatched. For instance, a crow looking at a mismatched pair would then select
the mismatched pair from their response choices. Nearly 78 percent of the time,
the birds succeeded. According to the researchers, the birds recognized that the
relationship between the two pairs of objects was the same. In other words, they
were making analogies.
Other scientists contend that a type of reasoning less sophisticated than
analogies could have produced the same results. For instance, the crows in the
analogy test could have simply chosen images with similar characteristics, such
as objects of the same color, instead of reasoning about the relationship
between the objects, to get the correct answer.
Some behaviors, like those employed in the analogy test, could have more than
one explanation, and until recently, scientists could only see what the birds
did, then make inferences about the mental processes behind the behavior.
Now, researcher John Marzluff and his colleagues at the University of Washington
are using positron emission tomography, or PET, scans to study which parts of a
crow's brain are active when it performs such tasks as recognizing friendly and
unfriendly birds. And he says that another team of researchers, at the
University of California at Davis, is preparing to use the same technique to
study the brain activity of New Caledonian crows, a species that makes
sophisticated tools. The team hopes to actually see the crows' brains at work
while they're crafting tools.
Corvids seem to understand that other birds have minds like theirs, and their
decisions often take into account what others might know, want or intend,
according to several studies of crows <http://www.ncbi.nlm.nih.gov/pubmed/25207993>,
and jays. Psychologists call this a theory of mind, and it's a fairly
sophisticated cognitive ability. Humans don't develop it until late in
childhood. Crows and their fellow corvids are social animals, much like
primates, so theory of mind probably offers significant evolutionary advantages.
For one thing, it may help prevent food theft. Crows and ravens often hide food
in caches and retrieve it later. "You can actually see them watching both the
other birds that they are with and the humans, and if they sense that they have
been seen, they will take that food and they'll go and hide it somewhere else,"
Innes said of the Maryland Zoo's ravens. The birds appear to realize that
watchers will know where they've hidden the food and might use that knowledge to
steal it later.
of several corvid species have documented this re-caching, as it is called.
Skeptics of the birds' advanced intelligence say simpler mental processes might
prompt re-caching, such as making an association between being seen and later
having a cache stolen.
Innes, however, is convinced that the re-caching is a sign that ravens have a
theory of mind, based on her observation of re-caching behavior in ravens at the
Maryland Zoo. "Definitely," she said. "I think it definitely indicates that."
Other test results are harder to dismiss <http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1691735/pdf/15306330.pdf>
as simple association. When researchers in Austria hid food behind a partition,
ravens found it, apparently by noticing where the humans were looking and
following their gazes to the hidden food. "You're using the person's gaze to
infer information about something you can't see," Marzluff said.
Brain imaging studies could settle the question, Marzluff said, because advanced
cognition in all animals uses different areas of the brain than simpler
Corvids' toolmaking is much more clearly the product of sophisticated cognition,
according to biologists who study them.
Several animals use found objects to get food, such as otters and sea gulls that
use rocks to crack shellfish, and apes that use sticks to fish termites out of
nests. But deliberately crafting tools is a much more sophisticated skill. Only
four species are known to actually make tools: humans, chimpanzees, orangutans --
and New Caledonian crows. Although other corvid species have learned to make and
use tools in labs, only the crows found on the Pacific island of New Caledonia
have been found to actually make tools in the wild.
With their beaks, the crows sharpen forked twigs into hooks for scooping larvae
and worms out of holes in wood. The crows often spend more than a minute finding
the right stick and then sculpting it into the right shape <https://www.youtube.com/watch?v=m8zCmj6z8VQ>.
Even chimpanzees don't craft their tools so meticulously, and some researchers
say that the crows' work is on par with very early human tools such as spears
and sharpened digging sticks.
New Caledonian crows even take steps to avoid losing their carefully crafted
tools. Biologists recently discovered <http://rspb.royalsocietypublishing.org/content/282/1808/20150278>
that the birds sometimes stash their hooks in holes, or simply stand on them,
when they aren't in use. The crows are especially careful when the risk of
losing their tools is greatest, such as when the birds forage in high branches.
The aptitude for toolmaking is probably an instinct for most corvids, as it is
for humans. Corvids use found objects as tools -- ravens and crows, for example,
drop nuts onto flat rocks to crack the shells -- and nearly all corvids seem to
have a knack for solving physical problems. In one set of experiments <https://www.youtube.com/watch?v=nTtDbyQTQV0>,
captive crows figured out how to bend wires into hooks to retrieve food from a
tube. And captive rooks, close relatives of crows and ravens, have done the same
It's unsurprising that chimpanzees and orangutans share so many abilities with
humans, because they are very closely related to us, but it's striking that
corvids share so many skills once believed to set humans apart. After all, birds
and mammals have spent the last 300 million years evolving on different paths,
which produced very different brain structures and bodies.
Parts of the brain that evolved earlier than 300 million years ago, such as the
primitive structures in the brainstem that control basic bodily functions, look
the same in most animals, including primates and corvids. But structures that
developed more recently, like those involved in cognition, are organized very
differently in birds than are they are in mammals.
Mammalian brains have evolved with what is called a laminar structure, in which
brain cells are organized in six layers that make up the cerebral cortex, or
forebrain. The cerebral cortex handles cognitive tasks, and it's especially well
developed in humans and our fellow apes, as well as other intelligent animals
such as dolphins and dogs. In the bird brain, a structure called the nidopallium
caudolaterale handles cognitive tasks, and it's especially well developed in
"All three of those animals have very large forebrains relative to the rest of
their brains, for their particular group," Marzluff said. "Certainly the
forebrain of a bird and a mammal differ, but they have the same sorts of
functions -- that is, you know, higher-level thought and processing of sensory
In birds' brains, cells form clusters called nuclei instead of layers. For
years, biologists held that the layered cerebral cortex gave mammals some
cognitive advantages, but research on corvids has cast doubt on that assumption.
That such distantly related animals with such different brains could evolve such
similar abilities is surprising, but when two different species face similar
evolutionary pressures, natural selection can lead to similar traits. Biologists
call this convergent evolution, and it's the same process by which birds and
bats both evolved wings. At some point, biologists say, the ancestor of today's
corvids must have found itself in an ecological niche where intelligence boosted
the odds of survival, so corvid brains evolved with cognitive abilities similar
to those of primates.
Convergent evolution may have led to similar wiring despite the differences in
physical structure between bird and mammalian brains. The network of connections
between areas of the brain looks very similar in corvids and primates, and one
recently published paper compared bird and primate brains to Apple and PC
computers. "At one level of analysis, they do the same things in a similar way,
but viewed from another perspective, their operating systems are indeed
different," wrote the author, Cambridge University psychologist Nicola Clayton.
In the coming years, the differences and similarities between corvids' mental
operating systems and those of mammals will be analyzed with brain imaging. At
that point, said Marzluff, we may have "some of those answers" to the question
of how smart crows really are.
Smith-Strickland is a freelance science journalist based in Kansas. Follow her
on Twitter: @RescueFins.