Staff at Brookfield Zoo are mourning the sudden death of a newborn dolphin. The female calf was nearly a week old. She was born to a 26-year-old dolphin, Allie, one of three Brookfield dolphins who were pregnant this summer.

The baby weighed around 40 pounds at birth and measured 3 feet long. At the time, Brookfield staff said the baby was healthy and strong. But by Wednesday, veterinarians started seeing signs that the baby, who was not named, wasn’t well. According to Dr. Michael Adkesson, Vice President of clinical medicine at the Chicago Zoological Society, the calf seemed weak, and the frequency and duration of nursing with her mother began to decline.

Adkesson says the first days of a dolphin’s life are extremely critical, and studies have shown that deaths of young calves in the first 30 days of their life account for the largest rate of loss to dolphin populations in the world.

“It’s not an animal like a primate where the mom’s able to carry the animal around, or a tiger or a lion where it’s able to be tucked back in a den,” he said. “The animals really come out in the water and have to really be able to go from the first minute of birth.”

Dolphins have to learn skills like swimming, eating, breathing and how to nurse right after birth. These are skills Adkesson says Allie was correctly teaching her offspring, but the baby’s health still continued to decline.

Veterinarians tried to intervene, including using CPR and other tactics, but they the dolphin died early Thursday.

Adkesson says Allie is doing well, health-wise, but that it’s hard to tell if or how she’s dealing with the loss.

“It’s difficult for us to really know that, in terms of how much they grieve, “he said. “Obviously, we know they’re very intelligent animals, but as far as the level of emotion that they feel, it’s not something that we can really speak to.”

The calf’s autopsy report is expected to come back next week.

For now, Brookfield Zoo staff is focused on its two other mothers-to-be, and the two, hopefully healthy, babies that will be swimming alongside them in the water this fall.

Lauren Chooljian is WBEZ’s Morning Producer/Reporter. Follow her @laurenchooljian.