Two extremely rare Sumatran tigers have celebrated their first month at San Diego Zoo Safari Park.

The unnamed cubs are gaining a pound of weight every three days, weighing in at ten and 11 pounds, although they are still too young to leave their enclosure and are being cared for by their mother, Delta.

When they are fully grown, a male can weigh 220 pounds.

There are only around 400 Sumatran tigers left worldwide, six of whom now live at San Diego Zoo.

Tigers face many challenges in the wild, from loss of habitat to human conflict, but the biggest threat continues to be poaching. Tigers are killed by poachers, who illegally sell their body parts, mostly for traditional medicines.