A border collie in the US has learned the names of more than 1,000 items, according to the scientists working with her.

Chaser has been intensively trained over three years by psychologists Alliston Reid and John Pilley of Wofford College in South Carolina, who wrote up their findings in the journal Behavioural Processes.

As well as seeming to know the names of all of her 1,022 toys, her trainers say she can categorise them by function or shape, something human children learn to do when they are about three years old.

There is some scepticism about Chaser's abilities - other dogs can perform similar tasks but not to such a high standard.

In 2004, border collie Rico was found to have a "vocabulary" of about 200 words by researchers at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany.

Meanwhile a border collie in Austria, known as Betsy, appears to understand more than 340 words.

It is thought the intensive training may be the key to Chaser's apparently massive vocabulary.