The discovery of stuttering song birds by a team of scientists has raised the prospect of new drugs and therapies to tackle the speech affliction in humans. David Rosenfield, a researcher at the Baylor College of Medicine in Houston, in the United States, told the American Neurological Association's annual meeting on Monday that a small minority of normally raised zebra finches had been found to abnormally repeat song sub-units - the equivalent of syllables. "These repetitions are not a part of normal song, just as stuttered repetitions in human speech are not a part of normal speech," said Rosenfield. The revelation that animals other than mankind can suffer the affliction is seen as a crucial step forward by neurologists, who have until now searched in vain for a non-human stutter. Neurological parallels between the tongue-tied birds and humans should provide scientists with clues to the nature of the disorder, which is now thought to be caused by some form of brain abnormality and not psychological problems. The zebra finches would also give scientists the chance to test new drugs that might make sufferers - estimated at about 1 per cent of the adult human population - fluent.