Humans may not be experiencing a pandemic baby boom, but Chicago’s Shedd Aquarium sure is.

Katrl, a Pacific white-sided dolphin, and Naya, a beluga whale, gave birth within 12 hours of each other late last month, the aquarium excitedly reported in a press release. And the 31-year-old beluga didn’t have just one, but two calves, an incredibly rare event which occurs to less than 1% of the species, previous research has found.

Sadly, Naya’s second calf — delivered hours after her first on Sunday, Aug. 30 — was stillborn, and the first calf was premature, weighs just 66 pounds and faces several developmental hurdles as a result of being a twin.

Still, that twin calves were born at all is remarkable.

“There is no documented case of twin beluga calves born in the wild. To our knowledge, Naya’s calf represents just the second known instance of a surviving twin in any cetacean species,” the aquarium wrote. “Naya is currently swimming with her surviving calf. Our hope is to witness nursing and bonding between the two, and significant growth in the calf, in coming days. Naya is recovering normally following the two deliveries.”

Then, on Monday, Aug. 31, Katrl, a 33-year-old dolphin, also went into labor. “Upon delivery, Katrl immediately helped the calf swim to the surface to take its first breath,” wrote the Shedd, adding, “Katrl is recovering normally.”

The dolphin baby and whale twins arrived just 10 days after another Shedd Aquarium beluga whale gave birth last month: Bella, a 14-year-old beluga welcomed a healthy baby boy on Aug. 21. Stunning video of the birth shows not only the miracle of marine life, but also the joy it brought to aquarium staffers.

“As the calf swam to the surface and took its first breath, it brought with it the palpable hope of new life and fresh beginnings — something we all appreciate,” said Shedd Aquarium President and CEO Dr. Bridget Coughlin.