Saving Javan rhinos from extinction starts with counting them – and it's not easy
Posted by admin on 31st May 2017

The Javan rhino (Rhinoceros sondaicus) is found only at the very western tip of the Indonesian island of Java, in the rainforest habitats of Ujung Kulon National Park (UKNP). However, this wasn’t always so. Many species have small natural ranges, but Javan rhinos once inhabited much of Southeast Asia. Now landscape changes, habitat loss and hunting have reduced their numbers to a precarious few. The last known Javan rhino in mainland Asia was poached in 2009. Today Javan rhinos are listed as critically endangered by the International Union for the Conservation of Nature.

Recovering any wild animal population with so few individuals remaining is very difficult. Small populations grow slowly even in the best of circumstances. And if even a few animals are lost to poaching, disease or other factors, the loss represents a relatively large proportion of the population.

It also is very hard to count small populations and characterize their distribution accurately. Often this critical information is poorly known, which makes it challenging for scientists to track the population and evaluate whether their actions are having positive effects. Nonetheless, scientists and the Indonesian government are forming a plan to rescue this imperiled species.

Map of Java, Indonesia. Ujung Kulon National Park is at the far left (west) end.
Burnesedays/Wikipedia, CC BY-SA

Why counting rhinos is hard

The rhino lineage has survived 50 million years through ice ages and attacks from prehistoric animals, such as the “dog-bear” (Hemicyon sansaniensis). Rhinos play a significant role in structuring ecosystems. The Javan rhino creates unique habitats within the rainforest by dispersing seeds, creating mud wallows and removing large amounts of understory plants. Losing it would mean a less diverse forest.

But despite almost a century of studies on the Javan rhino, we still know relatively little about them. The first estimate of the rhino population in UKNP, made in 1937, put their numbers at 20 to 25. Since then, at least 36 population surveys have attempted to count the rhinos, but most have failed to account reliably for the entire population or provide much insight into the factors that drive their distribution within UKNP.

Javan rhinos range over large areas of dense and swampy rainforest, and researchers rarely see them. Instead we find tracks and dung, which help us understand the habitats that rhinos use, but are rarely good indicators of population size. More recently, scientists set up camera traps to capture images of rhinos, but without high-quality images it was hard to tell individual animals apart.