The Santa Barbara Zoo’s second red panda cub has died, a zoo spokesperson announced Monday morning.

Two cubs were born to red pandas Ruby and Raj on July 2. One of the cubs died last week, and the second cub was moved into an incubator, according to zoo staff.

They noted that the first weeks of a red panda cub’s life are “an especially vulnerable time” and that mortality rates for cubs under one year old have been reported as high as 40%.

The second cub had been in intensive care and receiving around-the-clock care since July 19 because it wasn’t properly nursing from its mother, spokesperson Andrea Gruber said.

The cub had been in a temperature-controlled incubator, with tube and bottle feedings every three hours, as well as antibiotics and veterinary monitoring, according to Gruber.

The veterinary team saw changes to the cub’s breathing pattern on Saturday, and he was “declining rapidly” by Sunday, Gruber said.

“Despite intensive treatment during the last 12 hours, including fluid therapy, nebulization, adjustments to his antibiotic regimen, and eventually supplemental oxygen support, he did not survive,” she said.

The cub’s death is “an incredibly sad and disappointing outcome,” she said.

“While neonatal mortality can be high in red pandas, the loss of both cubs has been heartbreaking for everyone involved in their care.”

A necropsy showed a “significant amount of pericardial effusion (fluid surrounding the heart) and some congestion of the lungs,” Gruber said.

Additional testing is underway, she added.

The zoo’s red pandas Ruby and Raj are doing well and have been reunited in the habitat. Gruber said red pandas breed seasonally, so additional cubs would not be born until at least next year.