Endangered Amur leopard cubs born at Illinois zoo

Two endangered Amur leopard cubs have been born at the Brookfield Zoo in Illinois.

The 8-week-old male cubs are "thriving," Amy Roberts, the Brookfield Zoo's senior curator of mammals, told ABC News.

As they've grown, the cubs' caregivers have been able to tell them apart by their differing appearances and personalities, Roberts said.

The cubs have different spots, and one of them has a bolder personality than the other, Roberts said.

The last time the mama leopard, Lisa, gave birth, it was to only one cub, so she was the only one for him to play with, Roberts said. Now that Lisa has had twins, she's getting a bit of down time as they play with each other instead.

"They spend a lot of time stalking each other and wrestling each other," Roberts said.

The cubs were born on April 18 but their birth was just announced because veterinarians wanted to give the mother, Lisa, privacy as she bonded and cared for the cubs. During that time, zookeepers mostly monitored the mother and babies from a camera.

The photos were taken during the cubs' 8-week vaccinations, Roberts said. They will be placed in an outdoor habitat to be viewed by the public in mid-July, after they've had their second set of shots.

"It is our hope that guests will not only enjoy seeing these very charismatic cubs exploring and playing in their outdoor habitat, but will also gain an appreciation for the species and learn why conservation efforts are so important for this leopard," Roberts said.

Amur leopards are critically endangered and fewer than 65 are left in the wild, predominately in one isolated population in far east Russia, and a few in the Jilin Province of northeast China, according to the zoo. The biggest threats the leopards face are poaching, retribution hunting, a decrease in their habitat due to fires, logging and human settlement and a decline in their prey, the zoo said in a press release.

In 2013, the World Association of Zoos and Aquariums created the Amur Leopard Global Species Management Plan to help the species survive, according to the zoo.

There are currently 82 Amur leopards in 42 accredited zoos in North America, the release states. The nocturnal species are known for their keen senses of hearing, vision and smell and they live in temperate forests with cold winters and hot summers.

The cubs have not yet been named.