Ten of the smartest species revealed in 2009 have been listed out in a report from BBC's Earth News.
At number one is the albatross, which is smart enough to associate with killer whales in collecting food for its chicks, a strategy that the bird may adopt for efficiency.
Thanks to tiny cameras fitted on the seabirds' backs, scientists came to know that the albatross follows hunting killer whales, and tuck into the scraps left behind by the giant animals.
At number two is the chimpanzee, whose spatial memory is so precise that it can find a single tree among thousands in a forest.
The chimps also recall how productive each tree is, and can decide to travel farther to eat from those they know will yield the most fruit.
At number three is the octopus, which can scoop up halved coconut shells before scampering away with them so they can later use them as shelters.
Researchers said that it is the first example of tool use in octopuses.
At number four is the discovery by scientists that male bowerbirds which show superior intelligence are more sexually attractive to female birds.
At number five is the spider, a species of which can build a life-like model of its own body to distract predators.
The spider may be the first example of an animal building a life-size replica of its own body.
At number six is the rook, a close relative of the crow, which can repeat one of Aesop's fables by raising the water level in a pitcher so it can reach the liquid to quench its thirst.
At number seven is the golden eagle, which is smart enough to hunt and kill a comparatively large animal like the reindeer.
Extraordinary camera footage taken by a BBC crew showed an eagle swooping down and grabbing a calf, while another pulled out of an attack at the last minute.
At number eight is a plant found in the rainforests of Ecuador, which can pretend to be ill, to stop it being attacked by insect pests known as mining moths, which would otherwise eat its healthy leaves.
At number nine is the finding that chimpanzees are biologically programmed to appreciate pleasant music.
Infant chimpanzees innately prefer consonant over dissonant music, suggesting an appreciation of music is not a uniquely human trait.
At number ten is the discovery that it is not just humans that use aromatherapy, but blue tits as well.
The birds were found to line and disinfect their nests with bacteria-killing aromatic medicinal plants such as mint and lavender.