LONDON (Reuters) - Although they have brains about the size of a grain of rice, hummingbirds have superb memories when it comes to food, according to research on Monday.

No bird-brains these tiny creatures that weigh 20 grams (0.7 ounces) or less and feed on nectar and insects.

The research, reported in the journal Current Biology, suggests they not only remember their food sources but can plan with a certain amount of precision.

"To our knowledge, this is the first demonstration that animals in the wild can remember both the locations of food sources and when they visited them," said Susan Healy, of the University of Edinburgh.

Healy and scientists in Britain and Canada studied rufous hummingbirds in the Canadian Rockies. They found that the birds remembered where specific flowers were located and when they were last there, two aspects of episodic memory which was thought to be exclusive to humans.

"Hummingbirds that defend territories of many flowers remember which flowers they have recently emptied," Healy said in a statement.

The scientists tracked how often hummingbirds visited eight artificial flowers filled with a sucrose solution in the birds' feeding grounds.

They refilled half the flowers at 10 minute intervals and the other half 20 minutes after they had been emptied.

The birds' return to the flowers matched the refill schedules: flowers refilled at 10-minute intervals were visited sooner, according to the scientists.

"We were surprised that their timing abilities were so good and that they managed to cope so efficiently with as many as eight different flowers," said Healy.

The average rufous hummingbird migrates 2,000 miles in winter from Canada to warmer weather in Mexico. In the Spring, they return home to breed.

Scientists suspect the brains of hummingbirds became highly developed because of their long travel schedules and so they do not waste time and energy searching for food.