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Kya (left) and Neka, pictured long before she gave birth Saturday night.

(BENJAMIN BRINK/The Oregonian)

Here it is, the

cubs growing more adventuresome by the day.

The

at the have opened their eyes and are keeping their hungry, sleepy mother busy, a zoo spokeswoman said Tuesday afternoon.

"They're active and crawling out of their nest box and she's retrieving them," said Marcia Sinclair.

Keepers report that

, leaves her den to eat and sleep, luxuries she skimped on during the first couple days after giving birth. And as the video shows, she has to fetch the boldest of her cubs, who manage to scamper out of the nest box into the lions' larger indoor enclosure for romps through the hay.

The area is out of sight of

visitors.

Keepers say the lioness appears generally comfortable when they approach her enclosure to deliver food and water. When they get too close to the plywood nest box, however, Neka growls her disapproval.

Given that mother and cubs appear to be thriving, Sinclair said, the zoo's veterinary crew may have the opportunity to examine the little ones by midweek.

The cubs -- their genders unknown -- arrived between 8:30 p.m. and 10:30 p.m. Saturday. They're the first lions born at the zoo since the 1970s.

They'll likely go on exhibit at 6 to 8 weeks old.

Check out the video below:

– Katy Muldoon