Birds
Crow
Corvidae · also called crows, corvids
A crow is one of the smartest animals that is not a mammal. It makes hooked tools, plans ahead, remembers the face of a person who wronged it for years, teaches that grudge to its family, and gathers with other crows around a dead one in a way that looks unsettlingly like a funeral. It does all this with a brain built on a completely different plan from ours.
Overview
Crows are part of the family Corvidae, around 130 species — crows, rooks, ravens, magpies, jays, nutcrackers, choughs, and the jackdaw — on every continent except Antarctica and South America. All are omnivores and opportunists, and all have an unusually large, densely packed forebrain. They range from small jays to the common raven, one of the largest perching birds.
A different kind of brain
Corvids have one of the highest brain-to-body ratios of any birds, and on cognitive tests they perform at the level of a chimpanzee or a young child — despite having no neocortex. The processing happens in a dense forebrain region, the nidopallium, a case of intelligence evolving twice by separate routes.
Tools, faces, and funerals
The New Caledonian crow shapes and reuses hooked tools, carrying favourites between sites. Crows recognise individual human faces, mob people who have harmed them for years, and pass the reaction on to flockmates. And when a crow dies, others gather and call around the body, then treat that place and any nearby predator as dangerous.
Family life
Many crows are cooperative breeders, with grown young staying several years to help raise their siblings before leaving to breed.
Status
Crows as a family are Not Evaluated. Most are common and several are expanding into cities, but a number of island species are threatened, including the Hawaiian crow, or alala, which went extinct in the wild in 2002 and is being reintroduced from captivity.
Crow: common questions
How intelligent are crows really?
By the standards used for animal cognition, exceptionally. Crows and their relatives make and use tools, plan for the future, understand that hidden objects still exist, use analogy and causal reasoning, recognise themselves in some mirror tests, remember thousands of food caches, and recognise individual humans by face for years. New Caledonian crows in particular manufacture hooked tools and use them in sequence, a level of tool behaviour otherwise seen only in great apes. They achieve this with a brain built very differently from a mammal's, with no neocortex, but with a densely packed forebrain region called the nidopallium that supports similar processing, an example of intelligence evolving twice by different routes.
Do crows really remember human faces?
Yes, and there is solid experimental evidence. In a long-running study, researchers wore a distinctive mask while capturing and banding wild crows, then walked around campus wearing that mask or a different one on later days. The crows scolded and dive-bombed the capture mask for years, while ignoring control masks, and the hostile response spread to birds that had not been present at the trapping, apparently learned from the alarm calls and behaviour of others. Crows also learn which individual people are reliable sources of food and will follow and wait on them. This face memory helps them navigate a world full of humans, some dangerous and some useful.
What is the difference between a crow and a raven?
They are close relatives in the same genus, and ravens are essentially very large crows, but several features separate them. A raven is noticeably bigger, roughly the size of a buzzard, with a heavier bill, shaggy throat feathers, and a wedge-shaped rather than fan-shaped tail seen in flight. Ravens soar and tumble on the wing far more than crows and give a deep croak rather than a sharp caw. Ravens tend to be found in wilder country, in pairs or small groups, while many crows form large flocks and roosts and are more tied to farmland and towns, though these differences are not absolute.
Why do crows gather around a dead crow?
It appears to be danger learning rather than mourning in a human sense, though the two are not mutually exclusive. When crows discover a dead crow, they call loudly, which draws in other crows, and the group stays around the body for anywhere from minutes to a day. Experiments show that afterward the birds are more cautious about that location, about any predator seen near the body, and about people who were present, and they will avoid a food source that a dead crow was placed near. So the gathering seems to function as a way of identifying and remembering threats, information that is valuable to a long-lived, social, and highly intelligent bird.