Crows have a long-term memory so good that they can recall colours for at least a year, a Japanese study has shown. Birds that had identified which of two containers held food by the colour of its lid were still able to perform the task 12 months later, said Shoei Sugita, a professor of animal morphology at Utsunomiya University. Sugita said 24 birds were given the choice between containers with a red and green lid, which held food, and containers with a yellow and blue lid, which did not. After they had mastered the task, the crows were divided into groups and tested to see if they could recall the information they had learned. Even those creatures that had not seen the different coloured lids for a year were able to correctly identify where they would be able to find food, Sugita said. \"Our study has shown that the crows thought and used their memories to take action,\" Sugita said. Crows are a major nuisance in many Japanese cities, particularly Tokyo, where they rummage through rubbish left out for collection. The study was part-funded by Chubu Electric Power Company, in an effort to improve anti-nesting measures and protect the towers supporting power cables. Sugita says his work proves crows are intelligent creatures and measures used to foil them need to be carefully thought out. \"This study shows that there is no good way (to counter crows). But we can use their memories against them to create new measures,\" Sugita said.