Smartest Animals in the World: Apes, Dolphins, Crows and More

How do scientists measure animal intelligence?

Intelligence is hard to define even in people, so researchers look for specific abilities instead of a single score. The most common tests are:

• Problem solving: working out how to reach food in a puzzle box or a tube, often on the first try.
• Tool use and tool making: using objects, and better still changing them, to reach a goal.
• Memory: remembering places, faces, sequences or events for days or years.
• Social learning: copying skills from others, which can create local “cultures.”
• Communication: using calls, signs or symbols in flexible ways.
• Self-recognition: the mirror test, developed in 1970, checks whether an animal realizes that its reflection is itself.

Tests must suit each animal’s body and senses. A crow cannot use hands and a dolphin cannot pick up a stick, so a species that “fails” one test may simply be the wrong shape for it. Researchers also guard against the Clever Hans effect, named after a German horse that seemed to do arithmetic but, as psychologist Oskar Pfungst showed in 1907, was really reading tiny body cues from the people around it.

The smartest animals at a glance

1. Chimpanzees and bonobos

Chimpanzees are our closest living relatives, together with bonobos, and they are usually ranked as the most intelligent animals after humans. In 1960 Jane Goodall saw chimpanzees at Gombe in Tanzania strip leaves from twigs and use them, along with grass stems, to “fish” for termites, the first time tool making had been recorded in a wild animal. In West Africa, chimpanzees crack hard nuts with stone hammers on stone or wooden anvils, a skill young chimps take years to learn.

Different chimpanzee communities use different tools and habits, which many scientists call culture. Chimpanzees were also the first animals shown to pass the mirror test, in 1970. In memory experiments at Kyoto University, a young chimpanzee named Ayumu recalled the positions of briefly flashed numbers better than university students, although critics point out that he had far more practice.

2. Orangutans and gorillas

The other great apes are also highly intelligent. Orangutans use sticks to pry seeds from fruit and to probe for insects, and young orangutans stay with their mothers for about seven years or more, learning which foods to eat and how to process them. Charles Darwin was intrigued by an orangutan named Jenny at the London Zoo in 1838, which seemed to study its reflection in a mirror.

Gorillas show tool use and problem solving in captivity and occasionally in the wild, for example using a branch to test the depth of water. Their results on the mirror test are mixed: several studies found no self-recognition, while some gorillas raised with a lot of human contact did pass.

3. Dolphins

The bottlenose dolphin has a brain of about 1.5–1.7 kg (3.3–3.7 lb), slightly heavier than a human brain, and is one of the most studied animals in cognition research. Each dolphin develops its own signature whistle, which works much like a name: dolphins respond when they hear a copy of their own whistle. In Shark Bay, Western Australia, some bottlenose dolphins carry marine sponges on their beaks to protect them while foraging on the seafloor, a habit passed mainly from mothers to their young.

In 2001, two bottlenose dolphins at the New York Aquarium passed a version of the mirror test by swimming to a mirror to inspect marks on their bodies. Learn more in How smart are dolphins?

4. Elephants

Elephants have the heaviest brain of any land animal, about 5 kg (11 lb), with an estimated 257 billion neurons, around three times as many as a human, although most of them sit in the cerebellum, which controls movement. Older matriarchs appear to store knowledge that helps their families survive, such as the voices of other elephants and the location of distant water.

In 2006, an Asian elephant named Happy at the Bronx Zoo passed the mirror test by repeatedly touching a mark on her head that she could see only in the mirror. In other experiments, Asian elephants learned to pull a rope together with a partner to bring food within reach, and waited when their partner had not yet arrived.

5. Crows and ravens

Crows and ravens, members of the family Corvidae, rival apes on many tests. New Caledonian crows shape twigs and leaves into hooked tools to pull insect grubs from holes. In a famous 2002 study at the University of Oxford, a crow named Betty bent a straight piece of wire into a hook to lift a small bucket of food out of a tube.

Common ravens can plan ahead: in experiments they chose a tool or a token they would need many hours later. American crows remember the faces of people who have threatened them and scold them years afterward, and in 2008 the Eurasian magpie became the first bird shown to pass the mirror test. Read more in How smart are crows?

6. Parrots

Parrots combine large brains with long lives and complex social groups. The best-known example is Alex, an African gray parrot studied for about 30 years by Irene Pepperberg. By 1999, Alex could identify about 50 different objects, seven colors and five shapes, recognize quantities up to six, and understand ideas such as “bigger,” “smaller,” “same” and “different.”

Studies of brain anatomy help explain this: a 2016 study found that the brains of parrots and songbirds pack about twice as many neurons as primate brains of the same mass.

7. Octopuses

The octopus is the most intelligent invertebrate (animal without a backbone). A common octopus has about 500 million neurons, roughly two-thirds of them in its eight arms, which can explore and react partly on their own. Octopuses in aquariums learn to open screw-top jars, solve mazes and sometimes escape from their tanks.

In Indonesia, veined octopuses have been filmed carrying halves of coconut shells across the seafloor and assembling them into a shelter, one of the clearest examples of tool use in an invertebrate. Learn more in How smart are octopuses?

8. Pigs

Pigs are among the smartest domestic animals. In a 2009 experiment, seven of eight pigs that had spent a few hours with a mirror used it to find a bowl of food hidden behind a wall, while pigs with no mirror experience searched behind the mirror. In a 2021 study, pigs learned to move a cursor on a screen with a joystick held in their snouts. See How smart are pigs?

Other surprisingly clever animals

Intelligence is not limited to big-brained mammals and birds:

• Honey bees share the location of flowers through the waggle dance, and in 2018 experiments they learned to treat an empty space as a number smaller than one, a basic concept of zero.
• Bluestreak cleaner wrasse, a small reef fish, became in 2019 the first fish reported to pass a version of the mirror test, though scientists still debate the result.
• Rats solve mazes quickly and are widely used to study memory and learning.
• Sheep can remember the faces of dozens of other sheep for more than a year.

Myths about animal intelligence

“Scientists have measured the IQ of dolphins.” There is no IQ test for animals. Comparisons such as “as smart as a three-year-old child” are rough analogies based on single tasks.

“A bigger brain always means a smarter animal.” Brain size matters, but so does how many neurons are packed inside. Crows and parrots have small brains yet match apes on several tests, while the sperm whale has the largest brain of any animal.

“Goldfish have a three-second memory.” Experiments show goldfish can remember trained tasks for weeks or months.

“Animals that fail the mirror test are not self-aware.” Many animals rely mainly on smell or hearing, so a visual test may simply not suit them. For more examples of clever problem solving, see animals that use tools.