(WWJ) A female polar bear cub born at the Detroit Zoo November 28 did not survive her first week of life, and zoologists are struggling to understand why.

“We are all obviously grieving at the moment,” said Detroit Zoological Society Executive Director and CEO Ron Kagan. “Our animal care staff did everything they could to save the cub.”

The first hint something was wrong came when video surveillance showed the infant had stopped nursing. The cub was moved to an intensive-care nursery in the Zoo’s Ruth Roby Glancy Animal Health Complex yesterday where veterinarians and animal care staff immediately began administering life-saving measures.

Staff worked in shifts around the clock, providing fluids, antibiotics and infusions of polar bear blood plasma, while constantly monitoring the infant’s vital signs.

“The veterinarians were ultimately able to raise the cub’s low body temperature, and attempted to compensate for very low blood sugar from the outset,” Kagan said.

A necropsy is underway.

The cub’s parents are first-time mother, 6-year-old Suka, and 14-year-old Nuka.

How is mom holding up after the loss of her cub? “Suka appears to be healthy and calm,” Kagan said. “She initially showed promising maternal behaviors, but the cub stopped nursing yesterday.”

There are only 43 polar bears living in Association of Zoos & Aquariums-accredited zoos in the U.S.

Wild polar bears are found throughout five polar nations in the Northern Hemisphere, living along the shores of the Arctic Sea in the summer and on sea ice during the winter. Sea ice losses from greenhouse gas emissions threaten polar bear survival as these marine mammals rely on ice to hunt, to breed and, in some cases, to den. Polar bears are listed as threatened under the U.S. Endangered Species Act.