Two Sumatran Tiger cubs were born in early May, 2011 at Zoo Frankfurt in Germany, to mother Malea. Tiger cubs often stay with their mothers for about a year and a half, before venturing off on their own. They made their debut in the habitat on May 25 and seem to trade off between romping and napping. These pictures show the cubs at just five weeks old.

Photo credits: Emmanuel Keller

This tiger is named for its home, the Indonesian island of Sumatra. Javan and Bali tigers, the other two Indonesian tiger sub-species, are now both extinct. Sumatran tigers are a critically endangered species, with only about 400 remaining in the wild, according to the Sumatran Tiger Trust. About 350 live in captivity. Human impact and deforestation are the main reason for the decline of the Sumatran tiger population.