Photo courtesy of the Smithsonian’s National Zoo & & Conservation Biology Institute

Giant Panda Mei Xiang is approaching her small window of time this year when she can breed and conceive another panda cub, according to officials at the Smithsonian’s National Zoo.

The 18-year-old female panda is showing signs of being in heat—including being restless, pacing around, hanging out in a pool inside of her enclosure, and calling to male panda Tian Tian, according to zoo officials.

Scientists have also noticed that Mei Xiang’s outer genital area is swollen and pink, plus her estrogen levels have risen in her urine, which indicates that she’s close to ovulation. They will keep monitoring her to determine when she’s in “peak estrus.”

Mei Xiang, mother of Tai Shan, Bao Bao, and Bei Bei, will have about 36 hours to conceive this spring. When that brief window arrives, panda staff hope that she and Tian Tian can make it happen naturally.

Zookeepers said last month that Tian Tian has been feeling horny himself, showing signs of restlessness. And around that time, keepers started making changes to Mei Xiang’s enclosure to make it easier for them to enter her den to check on her and access a future cub.

The pair of pandas, however, have been unsuccessful in hooking up thus far. So as a backup, scientists plan to artificially inseminate Mei Xiang with Tian Tian’s semen.

And then, we wait.

Typically, it takes several months to tell if pandas are pregnant through an ultrasound. And by that time, the panda cub could be born within a week or so.

But let’s not get our hopes up too soon—there could be a chance that Mei Xiang experiences a false pregnancy, which she’s had in the past, according to zoo officials. Pandas can undergo pseudo pregnancies, in which they do everything they would if they were pregnant… except they aren’t. Zoologists will know if it’s a false pregnancy if her hormone and energy levels and behavior returns to normal.

But if the pregnancy is a go, panda keepers say Mei Xiang’s offspring would most likely be born around the end of September.