As he celebrates his second birthday Saturday, Po, the littlest panda at Zoo Atlanta, isn’t so little anymore.

He’s weighing in at a healthy 100 pounds, which is a handful for his nursing mother Lun Lun, who weighs 240.

He’s average for his age, but is rapidly moving toward his father Yang Yang’s weight of 300 pounds. In a matter of months, Po will be weaned and move to a solitary lifestyle, stretching the capabilities of exhibit space at Zoo Atlanta. That’s because Yang Yang and big brother Xi Lan already have separate exhibit space at the zoo.

The zoo has four enclosures on exhibit — two outdoors and two indoors — plus several off exhibit. “We’re OK with four separate panda enclosures, but it’s getting a little tight,” said Dr. Rebecca Snyder, curator of mammals.

Eventually Xi Lan, who is 4, will move to the Chengdu Research Base of Giant Panda Breeding in China, which is where his older sibling, Mei Lan, went in 2010.

(Mei Lan, you may remember, was considered a female, until a follow-up exam in China revealed something the American vets had overlooked.)

In other words, Lun Lun, 15, has had three male offspring, and Snyder said that a den full of male pandas is a bit like having a house full of boys. “Male pandas are like male humans,” Snyder said. “They play rougher.”

Since Mom serves in the role of playmate, “her job as a mom is a little harder than if she’d had all girls.” Po was named after the protagonist in “Kung Fu Panda,” which may or may not indicate a more rambunctious nature.

On Saturday, Po will enjoy an “ice cake,” composed of different layers of frozen, flavored, colored water, with special treats embedded inside and certain scents applied to the ice. Pandas enjoy those scents, and Po may spend more time rubbing the “cake” on himself than eating it.