Ravens are considered to be the most intelligent birds.
Picture from All About Birds
Ravens have displayed levels of high learning ability and the use of logic for solving problems. In one experiment, a raven had to reach a piece of meat dangling from strings bound to perches. To get to the food, a raven had to follow a series of actions: pull up a string stretch, hold a loop of it on the perch with a claw, then pull up another stretch and hold that loop. The birds had to repeat the action 6 times till getting the meat. The ravens turned out to be successful at it, but even after 30 tries, crows did not succeed.