Ravens can plan for the future. Octopuses create armour out of coconut shells. Orangutans can talk about the past.

Scientific research constantly gives glimpses into new dimensions of animal cognition. But intelligencewhich is so complex and encompasses such a wide range of adaptive abilitiesremains confoundingly tricky to measure.

One of the biggest challenges is our inability to comprehend how other species process information, says Kristina Horback, an assistant professor in the Department of Animal Science at the University of California, Davis, who studies the cognitive abilities of livestock animals.

Kanzi, a 39-year-old bonobo, became well-known for his language skills. He can communicate using hundreds of symbols that correlate to words.PHOTOGRAPH BY VINCENT J. MUSI, NAT GEO IMGE COLLECTION

Some animals have senses we cant even understand, such as sharks, which have an acute sensitivity to electrical currents, or insects, some of which can see ultraviolet light.

Our own senses skew how we perceive intelligence in animals. The mirror testan animals ability to recognise itself in the mirroris commonly used to assess capacity for self-awareness. Bottlenose dolphins, magpies, and manta rays are among the few species that have passed that test.

Because vision is key to humans, it makes sense that visual recognition of the self would be our default, Horback says. But what about species that rely on smell for identification, like swine? Visual information is not important to these species. Because the mirror test favors species that rely on vision over scent, it doesnt offer an objective measure of self-awareness.

We cant meaningfully compare intelligence among animals. One species might excel in one area but perform poorly in another and vice versa. And so much of an animals ability to pass a cognition test depends on its sensory abilities. Using human abilities as a comparative benchmark reveals the drawbacks of our attempts to measure intelligence across species.

Our vision is good, but not as good as hawks. Our hearing is good, but not as good as rats, says Edward Wasserman, a psychology professor at the University of Iowa who compares cognitive abilities among species. Our sense of smell, he says, is on the poor side, and dramatically outclassed by dogs.

As Wasserman puts it, How we contrive tests of intelligence may tell us more about the sensory abilities of animals than their intellectual abilities.

Add to that our tendency to value cognitive abilities that are human-like as evidence of higher intelligence. Many people say, I hear that pigs are smart, and sheep are dumb, Horback says. This is completely false. Pigs, like humans, are opportunistic omnivoresthey eat whatever they can find. Theyve evolved the ability, she says, to remember food locations and to use deception to keep other pigs away from their stashes. Sheep, on the other hand, are grazers. They have different skills, such as the ability to detect subtle flock movements. They do not need to solve complex food mazes or trick others away from food source, Horback says. It just does not make sense for sheep to have that particular cognitive skill.

Every species is adapted to its own environment. Animals generally have the cognitive abilities necessary to thrive. There are species which simply do not need to retain the capacity for complex problem solving [or] tool use, Horback says, pointing out that having more cognitive abilities than necessary would be wasteful for the animal's survival.

Barnacles do not move. Food comes to them, Wasserman says. Why should they engage in great feats of learning or reasoning?

Although scientists reject the notions of measures of absolute or comparative intelligence in animals, advances in technology are providing new insights.

Touchscreens in particular are proving to be a real game changer, Wasserman says. So long as animals can activate the screen by touching, nosing, or pecking, we can craft clever tests of their intelligence.

Here are 14 species from the animal kingdom that have demonstrated notable cognitive feats.

More here:
See 14 Animals That Have Shown Us Their Impressive Smarts - National Geographic Australia