Hidden cameras have captured proof that Javan rhinos are breeding in Indonesia's Ujung Kulon National Park, the last redoubt for the endangered mammals, conservationists said Monday.
Footage of two adults with two calves was taken in November and December last year by cameras hidden in the jungle of the rhino sanctuary on the southwestern tip of Java island, environmental group WWF said.
"This is fantastic news because before these camera trap images surfaced, only 12 other Javan rhino births were recorded in the past decade," WWF-Indonesia Ujung Kulon programme chief Adhi Hariyadi said.
"The population in Ujung Kulon represents the last real hope for the survival of a species that is on the brink of extinction."
The video clip show two females with their calves, one a female aged about a year and the other a younger male. They enter a small clearing in the jungle and appear to approach the hidden camera.
Environmentalists had believed there were only about 40 Javan rhinos left in the wild, but the camera data have led them to believe there could now be up to 50.
Of five rhino species, three including the Javan are critically endangered, mainly due to the growing demand for rhino horn.
The horns are ground into powder and used in traditional Chinese and other Asian medicines, although they have no scientifically proven medicinal value.
Ujung Kulon National Park authority chief Agus Priambudi said the new footage would help conservationists protect the last wild Javan rhino population.
A handful of Javan rhinos are also believed to exist in Vietnam but conservationists say those individuals, if they are still alive, are not a sustainable population.
"The camera enables us to know the position of the rhinos, their sex and whether there are pregnant rhinos among them. It's very important for the breeding process and conservation efforts," he told reporters.
"It will also help us to protect them from poaching... By knowing exactly where the rhinos usually roam, it's easier for our rangers to provide security for them."
Conservationists celebrated the discovery of the calves but warned that Ujung Kulon's rhino population remained extremely vulnerable.
Threats include poachers, habitat loss due to illegal clearing, disease from livestock that wander into the park from surrounding paddocks, tsunamis triggered by earthquakes and eruptions from the nearby Anak Krakatau volcano.
"We know that Ujung Kulon sits on a hot spot due to the active volcano, Anak Krakatau, and on plates with high seismic activity," WWF's Hariyadi said.
"The risk of extinction due to natural disaster is quite high."
With these threats in mind, officials are preparing to move up to five female and three male rhinos to another forest sanctuary on Java.
"We're really careful about executing the project and we're involving many experts," Hariyadi said.
Explore further: Killing off alien invaders – with maths