Sumatran tigers have darker orange fur and closer-together stripes than other tigers. Scientists think this helps them hide better in the thick, shady rainforest where they live. Stripes are amazing camouflage - in a forest full of dappled sun and shadows, a tiger can disappear in front of your eyes.
Like all tigers, the Sumatran tiger is a strong swimmer. The webbing between its toes makes it good in the water - and on Sumatra it sometimes swims across rivers to follow its food. Tigers are also some of the only big cats that really enjoy a good dip on a hot day.
Each tiger's pattern of stripes is unique, just like a fingerprint. Scientists put hidden 'camera traps' in the forest. When a tiger walks past, the camera takes its photo. Looking at the stripes on its sides, scientists can tell exactly which tiger they have seen, and where it has been.
There are only about 400 Sumatran tigers left in the wild. Indonesia has set up huge national parks - Kerinci Seblat, Bukit Barisan and Way Kambas - where they can live safely. Rangers patrol the forests every day to look after them, and many schools across Sumatra have 'tiger day' to learn about how to share the island with them.