Scientists and conservationists could search the forests of Indonesia for years and never get a glimpse of one of the Sumatran rhinos that once roamed freely throughout South-east Asia.
But on a quiet Sunday last November, after years of searching and another six months of staking out specific locations, a team of conservationists found Pahu - a small female Sumatran rhino - and began the process of rescuing her from her threatened habitat and isolation in the wilderness of Indonesian Borneo.
That day, Pahu (who was named after the river in the habitat where she was found) began a journey to help save her species.
With a team of veterinarians and conservationists working around the clock, Pahu made an arduous journey as a fleet of trucks and bulldozers carried her slowly over muddy roads to her new home.
Pahu is now the first resident of a Sumatran rhino sanctuary in Kutai Barat district in the East Kalimantan province of Indonesia.
Sumatran rhinos like Pahu are extremely unique and uniquely endangered. One of five different rhino species left on the planet, the Sumatran rhino is the closest living relative of the woolly rhino - a species that lived tens of thousands of years ago alongside the woolly mammoth - and is the smallest of all living rhino species.
ABOUT THE SPECIES
STATUS: Critically endangered
SCIENTIFIC NAME: Dicerorhinus sumatrensis
HEIGHT: 1m to 1.5m
WEIGHT: 600kg to 950kg
LENGTH: 2m to 4m
HABITATS: Dense highland and lowland tropical and sub-tropical forests
Sumatran rhinos are the smallest of the living rhinoceroses and the only Asian rhino with two horns.
They are covered with long hair and are more closely related to the extinct woolly rhinos than any of the other rhino species alive today.
Calves are born with a dense covering that turns reddish brown in young adults and becomes sparse, bristly and almost black in older animals. Sumatran rhinos compete with the Javan rhino for the unenviable title of most threatened rhino species.
While surviving in greater numbers than Javan rhinos, Sumatran rhinos are more threatened by poaching. There is no indication that the population is stable, and just two captive females have reproduced in the last 15 years.
The Sumatran rhino once roamed as far away as the foothills of the Eastern Himalayas in Bhutan and eastern India, through Myanmar, Thailand, possibly to Vietnam and China, and south through the Malay Peninsula.
Two different subspecies, the western Sumatran and eastern Sumatran, cling for survival on the islands of Sumatra and Borneo. Experts believe the third subspecies is probably extinct.
Source: World Wide Fund for Nature
The hairiest of all rhinos, its coat can be short and bristly, or wild and shaggy. It is even known to "sing" and is the most vocal of the five rhino species.
But after decades of poaching and the destruction of the forests it calls home, this special species faces the risk of extinction that grows more dire by the day. In 2015, Sumatran rhinos were declared extinct in the wild in Malaysia. Now, there are only about 80 Sumatran rhinos left in the world, and the remaining dozens of rhinos left live in Indonesia, where their isolation from one another puts them in extreme danger of total extinction.
Because they live in such fragmented populations (some consisting of only two to three rhinos), it is difficult for the animals to meet and breed. The longer female Sumatran rhinos do not become pregnant, the higher the risk that they will develop reproductive issues that prevent them from breeding at all. With diminishing odds on their survival in the wild, we decided to take action.
The conservationists, veterinarians and scientists who rescued Pahu last November were deployed by the World Wide Fund for Nature (WWF) and are part of a new coalition to save the species.
This operation was the first major project of the ambitious conservation breeding programme that aims to prevent the species from imminent extinction by finding, relocating and breeding these rhinos to increase their population, and eventually return them to the wild.
Leading the charge against this imminent extinction crisis, the government of Indonesia has developed an emergency action plan that established a national conservation breeding programme for the Sumatran rhino. In support of this monumental effort, the National Geographic Society, a global non-profit group, helped establish the Sumatran Rhino Rescue last September alongside WWF, The International Rhino Foundation, Global Wildlife Conservation and the International Union for Conservation of Nature.
This effort is the first-of-its-kind partnership to provide the resources, expertise and training needed to save this species.
An undertaking such as this is extremely challenging, risky and costly. Transporting one large animal is always a tricky process, and we still need to find and rescue many more, in order to ensure the species' survival in the long term.
With Pahu, over the next few months, we are working to ensure that she adapts to her surroundings and stays healthy.
She has around-the-clock monitoring by a team of top veterinarians, and we are cautiously optimistic she will thrive at the centre.
But we still have a lot of work to do before we are able to understand whether she will be able to have babies and help her species recover.
Then, there is even more work to do in order to find and relocate potential mates for her. To bring this species back from the brink of extinction, we need more organisations, foundations and individuals to support this effort.
An effort of this magnitude will require an estimated US$30 million (S$40.5 million) to support search, rescue and conservation breeding operations. The National Geographic Society and our founding partners have each contributed US$1 million to this effort and are looking for others to join us.
It is clear that the need to take action for species like the Sumatran rhino is growing each day.
In the past 50 years alone, actions like poaching, habitat degradation and human-wildlife conflict have led to the loss of more than 60 per cent of wildlife on the planet.
To prevent a global extinction crisis, scientists have shown that we need to set aside between 25 per cent and 75 per cent of the planet for nature, with many suggesting that an important first step is to protect 30 per cent by 2030.
This is why the National Geographic Society is supporting the Wyss Campaign for Nature - a US$1 billion investment to help communities, indigenous peoples and nations conserve 30 per cent of the planet in its natural state by 2030 - to help achieve this goal by creating and expanding protected areas, establishing ambitious international conservation targets, investing in science and inspiring conservation action around the world.
Efforts like Sumatran Rhino Rescue and the Wyss Campaign for Nature are vital to the idea that is central to the National Geographic Society's mission and should be to all others we share the earth with: to move towards a planet in balance.
We hope you will join us. Those who want to know more can go to https://savesumatranrhinos.org
• The writer is executive vice-president and chief scientist at the National Geographic Society.