[Photo] There are no more than 57 Javan rhinos left in Indonesia

Scientists in Indonesia have found evidence of four new rhino calves on the island of Java.

The discovery in Java's Ujong Kulon National Park has raised hopes that one of the world's rarest breeds of mammals could begin to re-populate.

Scientists from conservation group WWF made the discovery.

Park officials were first alerted to the new-born rhinos by tracks made by a mother and calf - a set of small footprints alongside larger ones.

In the following days, they found two more such tracks - too far away from each other to be made by the same family.

'Remarkable achievement'

Then, in another location, they spotted a fourth calf alongside its mother.

A WWF manager at the park described it as a remarkable achievement for conservation.

He said it was the first time in 40 years they had found evidence of so many new-born rhinos.

According to the head of Ujong Kulon, this year's baby boom could form part of a trend.

A census carried out last year suggested that seven new rhinos had been born.

That census put the park's rhino population at 57, though some figures put it at less than half that number.

Another five Javan rhinos are thought to live in Vietnam, making it one of the rarest mammals in the world.

Poaching as well as threats to their natural habitat have contributed to its decline.

Indonesia has set up habitat protection programmes to safeguard the rhinos' food sources and environment inside the National Park.

Part of this programme, say officials, involves leading bulls into the open areas so that rhinos don't have to compete with them for food inside the jungle.